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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > DIY Guides > Hard Brake Pedal DIY (e9x) - vehicles up to 09/2007



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Hard Brake Pedal DIY (e9x) - vehicles up to 09/2007
Published by Built My Way
09-24-2011
Hard Brake Pedal DIY (e9x) - vehicles up to 09/2007

Hey guys. I've put together this (long-ish) report and a DIYer pertaining to the morning hard brake pedal issue found in 3 series e9x up to Sept 2007 (See ‘The Trouble’ section below). There's not a whole lot of help out there on the topic and thought I could share some of my experience as I've resolved the issue on my own vehicle. The best part is that the fix is something that can be done without expensive repair work to your vehicle and without disconnecting components that are going to trigger any codes. It just takes a bit of time to physically get to the problem area and a lot of patience. Also, I can’t guarantee if this will work for you. It all depends on how well you follow the procedure and there’s a chance that the problem could stem from something else too. A good way to find out if your vehicle is a likely candidate for the fix is to perform ‘The Test’ section below. If you have the time, you may want to go ahead and perform the DIY anyway for the few dollars it’ll cost you.

The Trouble:
Many forum members have experienced a change in the feel of the brake pedal and have had some difficulty starting up their vehicles in the mornings because more effort is needed to extend the pedal far enough down to trigger the brake pedal switch. There are complaints that the pedal becomes significantly harder to press down on when the car has been parked for long periods of time. Some of you with manual trannys that park on an incline had not only experienced the hard pedal effect but also the loss of normal braking capability and found yourselves struggling to stop the car from rolling and had to employ the hand brake. Drivers of automatics obviously do not rely on braking for the purpose of holding the vehicle in place prior to engine start up but like the manuals, do need the pedal to extend far enough down to start the vehicle. Don’t let anyone tell you that the hard brake is normal. It’s not!

The Vacuum and Braking Basics:
With the engine on, air is constantly being drawn out of your car’s brake booster via a vacuum line which runs from the booster housing to the engine. Basically the vacuum creates suction on a diaphragm within the brake booster which lessens the force required on the brake pedal used to operate the master cylinder. A check valve is mounted in the vacuum line at the front of the brake booster to prevent air from rushing back in, allowing the booster to maintain a vacuum after the engine is turned off. This now gives the driver up to 4 good normal pumps of the brake pedal to prevent the car from rolling as he prepares to start the engine. This also allows for the driver to easily stop the car in case of an emergency if the engine fails and shuts down. Any loss of this vacuum makes the brake pedal feel harder than usual to the touch and stopping although possible will take longer to achieve which could result in an accident. As mentioned in the previous paragraph, loss of vacuum can also make starting the engine difficult because more force is required by the driver to push the pedal down far enough to trip the brake pedal switch.

The Culprit:
Below is the related SIB. The trouble is that it doesn’t go deep enough into solving the problem. In fact for me I find it somewhat misleading, making the reader believe that the problem lies within the actual check valve/hose assembly which in my case was not true. In fact the culprit ended up being the little rubber gasket P/N 34336765316. It's purpose is to allow the valve/hose assembly to fit snug into the orifice of the brake booster housing. I believe that slight shrinkage and/or hardening of an already undersized gasket combined with vehicle vibrations led to the loosening and ultimately the loss of vacuum from around the sealing surface. The leak is so slow that it could only be detected by way of the brake pedal of vehicles parked over several hours, usually over night. If this was the case, the degree to which shrinkage/hardening occurs could vary with each vehicle. In essence, some gaskets leak, some don’t. BMW does not directly make mention of this gasket in the SIB. Repair instruction RA 34 33 051 referenced in the SIB calls for a sealing ring to be replaced ‘if necessary’. Hmm! Also, my local dealership couldn't say whether or not the gasket had been resized for these vehicle years so we may see this problem resurface now and again.

See item #4 and #8 on link:
http://www.realoem.com/bmw/showparts...56&hg=34&fg=27
Note the discrepancy between the SIB p/n for the vacuum pipe (check valve/hose assembly) and p/n on the diagram.

The SIB p/n is for a different beast (see link, item #12):
http://bmwfans.info/parts/catalog/E8...ke_servo_unit/

SI B34 06 07
Brakes November 2007
Technical Service

SUBJECT
Additional Effort Required to Press Brake Pedal Prior to Engine Initial Start
MODEL
E90, E91, E92, E93 (3 Series) produced up to 9/07
SITUATION
A customer may report increased brake pedal effort prior to engine start. This situation can occur if the vehicle sits for extended periods of time. Although the brake pedal can be depressed, the customer may note a change in pedal feel.
CAUSE
The vacuum check valve, fitted at the brake booster, may leak due to component tolerances within the valve assembly.
CORRECTION
Replace the vacuum valve and hose assembly for the brake booster; refer to Repair Instruction RA 34 33 051.
PARTS INFORMATION
Part Number
Description
Quantity
34 33 7 577 336
Vacuum Pipe
1
WARRANTY INFORMATION
Covered under the terms of the BMW New Vehicle Limited Warranty.
Please refer to the latest KSD for all applicable labor operations and allowances.
If the appropriate labor operation is not contained in KSD, then a work time labor operation should be used.
Defect Code
34 33 00 14 00
[ Copyright © 2007 BMW of North America, LLC ]


The Test:
Note: Keep in mind to use a soft touch and a keen ear as you perform this.
1. Remove the black plastic cover from directly over the brake booster unit/brake fluid reservoir area. (Under the hood near the back in line with the steering wheel) The cover has two clips and a rubber tie down.

2. Please Note: Owners with manual trannys make sure you’re in neutral and apply your hand brake. Step on the brake pedal only to start the engine then remove foot from brake. After about 10 seconds turn the engine off keeping your foot off the brake at all times and please Do Not Step On The Brake Pedal At Any Time During The Remainder Of This Test!!! This is to ensure that a full vacuum exists within the brake booster.

3. Use a trouble light to locate the check valve on the front of the brake booster. You’ll find it tucked just below the black cylindrical component of the DSC hydraulic unit.
Note: Don’t let the maze of hydraulic lines deter you from doing any of these steps.

4. Use a long flathead screwdriver or reasonable facsimile to reach down between the hydraulic lines and gently press on the rubber gasket located between the check valve and the booster. Push near the gasket’s edge closest to the booster. You should be able to hear a hissing sound as air enters through the seal. If not, push just a bit harder trying not to damage the gasket or mar the surface of the booster orifice. I only had to push lightly before I heard air.

5. To confirm your findings, apply moderate pressure to the check valve using the screwdriver tip to see how the gasket responds. Does the gasket appear somewhat loose and can you hear air? If you heard air in parts 4 and/or 5 then go directly to the DIY below.

The DIY:
This DIY is based on a LHD power brake unit only. Some units on RHD vehicles are configured differently. ‘335rocks’ has replied to my post by submitting RHD pictures and a description and has opted to replace the gasket. My concern is that the gasket has not been redesigned and that the problem may show again.

Most of the following procedure is made up of steps just to get access to the rubber gasket. The area around the DSC hydraulic unit/ brake fluid reservoir/ brake booster is congested to say the least and getting a hand down to the lower half of the brake booster where the gasket resides is ‘almost’ impossible without having to completely disconnect hydraulic lines and remove the DSC unit. BMW calls for complete removal of the DSC unit first but we ain’t goin’ there!

You’ll find this DIY somewhat lengthy but I wanted to throw in plenty of detail as pictures are few and far between. Essentially we need to get to the rubber gasket which is located on the brake booster and apply a good size bead of gasket making material around the outer edge. Then we need to get a hand in there to ‘gently’ press the bead to make an air tight seal with the booster front. Too much pressure on the bead will only thin it out. Please, please, if you discover easier ways to do this fix then by all means feel free to share the details.
Also, plan to do this procedure when you can let your vehicle sit afterwards to allow the gasket material to cure. Find out the drying time on the back of the tube of gasket making material.
Let’s get to work!

I’m using steps 1 through 5 part of txusa03’s DIY procedure for changing spark plugs to remove the cowling under the micro filter housing.
http://www.e90post.com/forums/showthread.php?t=174217 (Thank You txusa03) His third picture is a nice shot of the DSC hydraulic unit/reservoir/brake booster compartment.
This will give you full exposure to the brake lines and check valve/hose assembly, etc. He lists tools that will be required. You obviously wont be needing all of them. In addition you will need:
- One tube of gasket maker (I used flexible non-hardening Permatex Black … not sure what it’ll do to the paint on the booster though) You may know of a better material for this purpose.
- Long shank flathead screw driver
- 10mm socket with extension bar
- A heavy gage wire coat hanger
- Trouble light
- Ideally a small hand with a long arm 

Step 1. Remove the micro filter. Use the 5/16 hex socket and remove 6 screws and just lift the micro filter housing out.

Step 2. Remove both covers on each side of the micro filter. Each one of these cover has 2 clips and a rubber tie down (red circle), locate and pop both clips loose, then pull the cover up and out of the rubber tie down. With these covers removed, you should see another hex screw (yellow circle) that hold the cowling in place. Remove these last two hex screws as well (one on each side).

Step 3. To remove the cowling you need to pull out the rectangular harness that holds the wiring.

Step 4. Behind the rectangular harness you will see additional wire tubing held on the underside of the cowling. Unclip those 3 clips and pull the wire tubing down

Step 5. Before you remove the cowling, unhook any other wiring that is still attached to the top side of the cowling. Now pull the cowling straight out toward the front of the car and tilt it up a bit as you pull (it helps to wiggle and work each corner loose as you go along).

Step 6. Removing the black plastic bulkhead (located between the engine compartment and the brake booster compartment). Disconnect the brake booster check valve/hose assembly at this location. Pull the end of hose through the bulkhead. Next, carefully remove the bulkhead by pulling on the four tabs that hold it in place, swing it up and separate it from the brake line by pulling away.

NOTE: Do not disconnect any wiring to the DSC hydraulic unit when performing the next steps or unless you want to trigger a code. Also, do not disconnect any of the hydraulic lines from the DSC unit.

Step 7. Unbolting and raising the DSC hydraulic unit. This allows you to gain access to the rubber gasket with your fingers and also allows more room to remove the check valve/hose assembly from the booster. Use the 10mm socket and extension bar to remove the three DSC hydraulic unit hold down nuts. Be carefully getting them out. A magnetized socket would be best. Find an old metal coat hanger to have at the ready. Roughly configure the hanger to suspend the raised DSC unit from the underside of the hood. There’s a small hole in just the right place in the hood. The brake lines are flexible enough to allow the DSC unit to be lifted up and over the hold down bracket bolting. Some of the lines have flex hoses connected which make lifting easier. Please use caution and pull the DSC unit up firmly being careful not to kink any of the attached brake lines. Use common sense. The unit can be pulled a little towards the side of the car as well to help clear a way. Adjust the length of the coat hanger to suspend the DSC unit. Keep it tight in place.

Step 8. Removing the brake booster check valve/hose assembly. Slip the flat head of the long screw driver between the check valve and brake booster and with a twisting motion, gently pry the valve out of the booster. The rubber gasket ‘should’ remain attached to the booster. Warning: Do not remove the gasket. It’s a bitch to put back… I know. Pull the check valve/hose assembly completely out of the compartment and put aside.

Step 9. Applying gasket material to the rubber gasket. Open the tube of gasket maker and attach the long nozzle applicator that should come with it. Apply a bead of gasket material liberally around the circumference of the gasket trying to stay in as close to the booster as possible. Avoid getting any gasket goop on the gasket face. Use the long screw driver to rotate the rubber gasket as you apply the material.

Step 10. Making an air tight seal between the rubber gasket and the brake booster.
Note: this step must be done without rotating the rubber gasket otherwise the gasket bead will not seal properly. By suspending the DSC unit I’ve now created a space just wide enough to slide my right hand in, palm side against the booster. My hand is jammed against the DSC bolting bracket on the wheel well but I can feel the entire rubber gasket with my index and middle fingers. The back of the right hand should almost be touching the back of the DSC unit. Now lightly run a finger around the gasket material to form a nice thick air tight bead while pressing it lightly against the booster and rubber gasket. There is no need to press hard. Just make good contact with the booster.

Step 11. Making an air tight seal between the check valve/hose assembly and the rubber gasket. This is kind of a good measure thing that I decided to do while I had the hose assembly out. Apply a small bead of gasket material to the check valve seat that fits against the rubber gasket. Note: Do not apply gasket material to the barbs on the valve.
Fish the check valve/hose assembly back into position and use the screw driver to push it home.
DO NOT TURN THE ENGINE ON UNTIL THE GASKET MATERIAL IS COMPLETELY DRY. (8 HOURS)
Well that’s it! Time to put everything back together. I think the DSC module hold down nuts require 8 Nm of torque. (6 ft-lbs)

The End:
Good luck everybody. Just think! No more hard brake pedal. Woohoo!
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  #1  
By 335rocks on 10-10-2011, 05:26 PM
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Many thanks for writing the DIY. I have had this problem for over a year and it's great to finally have this sorted. I didn't quite follow your DIY as my car is RHD and the vacuum hoses and access is different, but it gave me some good ideas to where my vacuum leak was. My garage had previously changed the pipes and check valve in an attempt to fix this, but it didn't help. However they had not changed rubber gasket, so trying to replace this was worth a shot. To be on the safe side I decided to change both the gasket and check valve.

As luck is the gasket is a lot more accessible on a RHD car and with a few long tools it's possible to replace it fairly easy. So I chose this option rather than going down the gasket maker route.

I have added a few pictures here that may help others see what the gasket and check valve looks like.

Gasket (bottom/side)
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Gasket (top)
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Brake check valve (RHD and it's quite different shape than the LHD) (Pulls straight out of gasket, other end can be disconnected quite easy by pushing the white tab in and pulling the pipes apart (remember to reduce the pressure by pumping the brake pedal). )
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Gasket in place on brake booster (RHD)
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Easy to fit new gasket by slipping you hand down the gap and then press the gasket into place. You may need some leverage to push the check valve hose back in again as it's pretty tight there. I used a long screw driver and used the side (not the end as this may do damage to the valve) to apply pressure and push it in.
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  #2  
By Built My Way on 10-11-2011, 06:09 AM
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Quote:
Originally Posted by 335rocks View Post
Many thanks for writing the DIY. I have had this problem for over a year and it's great to finally have this sorted. I didn't quite follow your DIY as my car is RHD and the vacuum hoses and access is different, but it gave me some good ideas to where my vacuum leak was. My garage had previously changed the pipes and check valve in an attempt to fix this, but it didn't help. However they had not changed rubber gasket, so trying to replace this was worth a shot. To be on the safe side I decided to change both the gasket and check valve.

As luck is the gasket is a lot more accessible on a RHD car and with a few long tools it's possible to replace it fairly easy. So I chose this option rather than going down the gasket maker route.

I have added a few pictures here that may help others see what the gasket and check valve looks like.

Brake check valve (RHD and it's quite different shape than the LHD) (Pulls straight out of gasket, other end can be disconnected quite easy by pushing the white tab in and pulling the pipes apart (remember to reduce the pressure by pumping the brake pedal). )
Gasket in place on brake booster (RHD)

Easy to fit new gasket by slipping you hand down the gap and then press the gasket into place. You may need some leverage to push the check valve hose back in again as it's pretty tight there. I used a long screw driver and used the side (not the end as this may do damage to the valve) to apply pressure and push it in.
Happy to hear about your brakes. Thanks for the photos and your input. I didn’t know that the vacuum line configuration was different in the RHD 3 series. BMW North America really confused matters when they referenced this style of vacuum pipe in their SIB. I’ll be going back to my report to make mention of the RHD config.

Did you happen to notice if the new gasket was larger than the old one? My fear is that the problem may occur again if using the same size gasket.

Cheers
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  #3  
By 335rocks on 10-13-2011, 05:28 PM
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Quote:
Originally Posted by Built My Way View Post
Happy to hear about your brakes. Thanks for the photos and your input. I didn’t know that the vacuum line configuration was different in the RHD 3 series. BMW North America really confused matters when they referenced this style of vacuum pipe in their SIB. I’ll be going back to my report to make mention of the RHD config.

Did you happen to notice if the new gasket was larger than the old one? My fear is that the problem may occur again if using the same size gasket.

Cheers
The new gasket looked pretty much identical and I don't think there was any difference, but I didn't spend a lot of time comparing them. I suspect that the tolerance issues were actually on the check valve and not the gasket. The old gasket did not have any visual damage to it and there were only a slight indentation from the barbs in the rubber gasket.

A new gasket is £3 and the check valve is £17, so for the hasle I just replaced both.
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  #4  
By Needler56 on 12-11-2012, 02:09 PM
This is great info. I had the check valve replaced and the hard brake pedal went away for about a week. Now, it's happening more than before I replaced it. Gasket just arrived so hopefully it'll fix it.
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  #5  
By PhaseP on 02-26-2013, 07:35 AM
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I replaced the check valve assembly hose and the rubber gasket last week. I have a 2006 e90, and I had this stiff brake pedal for a while. While under warranty I complained about it to dealership, they first changed the check valve hose assembly according to the SIB (TSB). It didn't fix it, I complained more, BMW center told them to change the brake booster altogether, didn't fix it either. After that they said it is the way these cars are, nothing we can do! I have a 2001 Corolla, it holds its brake vacuum even after days of sitting parked, same for a 2003 other car I have, how can it be normal! Anyway, recently the stiff pedal issue started to happen even minutes after shutting down the car. So it was leaking vacuum faster now. After reading this post, and not to leave anything to chance since I had been bothered with this so long, I bought a new vacuum hose with check valve, new rubber gasket, some flexible gasket maker RTV silicone (it is a blue one).

I used the instructions here, to gain access to the area. For removal of the old gasket, I suggest making something like a fish hook from a copper wire and place it in the gasket hole so that when it comes out you can fish it out of there. For placing the new gasket, I had trouble initially. My hands are wide and I could hardly touch the gasket area with my fingers. So I wrapped a loop with a thin copper solid hookup wire around the new gasket, on the thick lip part of it, not on the grove that goes into the hole in the brake booster. This way I could lower and position the new gasket with the wire from top of the engine with one hand, and push it in place with a long and big screw driver with the other hand. Before doing this, I had placed a small bead of RTV gasket maker only into the grove on the gasket that goes in to the hole.

After placing the gasket into the brake booster, again not being able to reach my hand in there effectively, I used a hex socket attached to a universal joint and then to an extension bar to push the check valve into the gasket. I used a socket big enough such that it fits to the had of the check valve.

The old gasket was exactly same as the new gasket I had bought. But I noticed brown dirt on all around the sealing grove on the old gasket, which was proof that it wasn't sealing properly, otherwise it would have no dirt in those places.

The new updated 2009 dated (at least once more) check valve assembly had a black head rather than the gray one. (which was already after the TSB, had 2008 date on it). The difference I noticed, the old check valve is one way, it allows air in one way, and blocks the other way. The new check valve does this same, but also if there is air pressure towards the brake booster, it lets this pressure to outside. The older check valve was working fine when I had tried to blow from each and of the pipe.

So the problem here is the gasket not sealing well as the OP brought to attention. I wish BMW could have figured this out, instead of replacing the whole brake assembly as an attempt to fix it.

It has been couple of days and my brake pedal is no longer stiff after car sitting down. And not only that, I immediately noticed the brake pedal response of the car got better. It became the same touchy/sensitive brake pedal like the way I remember it when it was brand new in 2006. So my leak was progressing by time that it was starting to effect even during driving.

Thanks again for your post, it allowed me to get rid of this long pesky problem!!
Last edited by PhaseP; 02-26-2013 at 05:04 PM. Reason: Fixed some grammar
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  #6  
By Built My Way on 02-27-2013, 09:18 AM
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Quote:
Originally Posted by PhaseP View Post
I replaced the check valve assembly hose and the rubber gasket last week. I have a 2006 e90, and I had this stiff brake pedal for a while. While under warranty I complained about it to dealership, they first changed the check valve hose assembly according to the SIB (TSB). It didn't fix it, I complained more, BMW center told them to change the brake booster altogether, didn't fix it either. After that they said it is the way these cars are, nothing we can do! I have a 2001 Corolla, it holds its brake vacuum even after days of sitting parked, same for a 2003 other car I have, how can it be normal! Anyway, recently the stiff pedal issue started to happen even minutes after shutting down the car. So it was leaking vacuum faster now. After reading this post, and not to leave anything to chance since I had been bothered with this so long, I bought a new vacuum hose with check valve, new rubber gasket, some flexible gasket maker RTV silicone (it is a blue one).

I used the instructions here, to gain access to the area. For removal of the old gasket, I suggest making something like a fish hook from a copper wire and place it in the gasket hole so that when it comes out you can fish it out of there. For placing the new gasket, I had trouble initially. My hands are wide and I could hardly touch the gasket area with my fingers. So I wrapped a loop with a thin copper solid hookup wire around the new gasket, on the thick lip part of it, not on the grove that goes into the hole in the brake booster. This way I could lower and position the new gasket with the wire from top of the engine with one hand, and push it in place with a long and big screw driver with the other hand. Before doing this, I had placed a small bead of RTV gasket maker only into the grove on the gasket that goes in to the hole.

After placing the gasket into the brake booster, again not being able to reach my hand in there effectively, I used a hex socket attached to a universal joint and then to an extension bar to push the check valve into the gasket. I used a socket big enough such that it fits to the had of the check valve.

The old gasket was exactly same as the new gasket I had bought. But I noticed brown dirt on all around the sealing grove on the old gasket, which was proof that it wasn't sealing properly, otherwise it would have no dirt in those places.

The new updated 2009 dated (at least once more) check valve assembly had a black head rather than the gray one. (which was already after the TSB, had 2008 date on it). The difference I noticed, the old check valve is one way, it allows air in one way, and blocks the other way. The new check valve does this same, but also if there is air pressure towards the brake booster, it lets this pressure to outside. The older check valve was working fine when I had tried to blow from each and of the pipe.

So the problem here is the gasket not sealing well as the OP brought to attention. I wish BMW could have figured this out, instead of replacing the whole brake assembly as an attempt to fix it.

It has been couple of days and my brake pedal is no longer stiff after car sitting down. And not only that, I immediately noticed the brake pedal response of the car got better. It became the same touchy/sensitive brake pedal like the way I remember it when it was brand new in 2006. So my leak was progressing by time that it was starting to effect even during driving.

Thanks again for your post, it allowed me to get rid of this long pesky problem!!
How many BMW engineers does it take to screw in a light bulb? None. According to their calculations the problem doesn't exist.

Thanks for your input. Wow, yours was in really bad shape.
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  #7  
By Beefy on 06-14-2013, 05:26 AM
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Quote:
Originally Posted by PhaseP View Post
I replaced the check valve assembly hose and the rubber gasket last week. I have a 2006 e90, and I had this stiff brake pedal for a while. While under warranty I complained about it to dealership, they first changed the check valve hose assembly according to the SIB (TSB). It didn't fix it, I complained more, BMW center told them to change the brake booster altogether, didn't fix it either. After that they said it is the way these cars are, nothing we can do! I have a 2001 Corolla, it holds its brake vacuum even after days of sitting parked, same for a 2003 other car I have, how can it be normal! Anyway, recently the stiff pedal issue started to happen even minutes after shutting down the car. So it was leaking vacuum faster now. After reading this post, and not to leave anything to chance since I had been bothered with this so long, I bought a new vacuum hose with check valve, new rubber gasket, some flexible gasket maker RTV silicone (it is a blue one).

I used the instructions here, to gain access to the area. For removal of the old gasket, I suggest making something like a fish hook from a copper wire and place it in the gasket hole so that when it comes out you can fish it out of there. For placing the new gasket, I had trouble initially. My hands are wide and I could hardly touch the gasket area with my fingers. So I wrapped a loop with a thin copper solid hookup wire around the new gasket, on the thick lip part of it, not on the grove that goes into the hole in the brake booster. This way I could lower and position the new gasket with the wire from top of the engine with one hand, and push it in place with a long and big screw driver with the other hand. Before doing this, I had placed a small bead of RTV gasket maker only into the grove on the gasket that goes in to the hole.

After placing the gasket into the brake booster, again not being able to reach my hand in there effectively, I used a hex socket attached to a universal joint and then to an extension bar to push the check valve into the gasket. I used a socket big enough such that it fits to the had of the check valve.

The old gasket was exactly same as the new gasket I had bought. But I noticed brown dirt on all around the sealing grove on the old gasket, which was proof that it wasn't sealing properly, otherwise it would have no dirt in those places.

The new updated 2009 dated (at least once more) check valve assembly had a black head rather than the gray one. (which was already after the TSB, had 2008 date on it). The difference I noticed, the old check valve is one way, it allows air in one way, and blocks the other way. The new check valve does this same, but also if there is air pressure towards the brake booster, it lets this pressure to outside. The older check valve was working fine when I had tried to blow from each and of the pipe.

So the problem here is the gasket not sealing well as the OP brought to attention. I wish BMW could have figured this out, instead of replacing the whole brake assembly as an attempt to fix it.

It has been couple of days and my brake pedal is no longer stiff after car sitting down. And not only that, I immediately noticed the brake pedal response of the car got better. It became the same touchy/sensitive brake pedal like the way I remember it when it was brand new in 2006. So my leak was progressing by time that it was starting to effect even during driving.

Thanks again for your post, it allowed me to get rid of this long pesky problem!!
I have replaced both the vacuum hose (check valve) and the gasket, but the problem still there, I don't know what to do
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  #8  
By PhaseP on 06-15-2013, 10:17 AM
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Quote:
Originally Posted by Beefy View Post
I have replaced both the vacuum hose (check valve) and the gasket, but the problem still there, I don't know what to do
Did you add some sealant RTV to the gasket groove? I had used this one

http://www.permatex.com/products/pro...t-maker-detail

and waited a while before starting the car until it cures. Mine is still good, no vacuum lost in the mornings.

If this doesn't fix you then have vacuum leak some where else.
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  #9  
By Orb on 11-08-2013, 09:14 AM
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This is a good post in this section but needs some clarifications. If you replacing the check valve house assembly it will be a good idea to replace the seal. The method from “PhaseP” works well if you are creative in rigging up an installation tool for the seal.

There is nothing wrong with the seal design but a better design could have been used. The sealing takes place in the radial grove of the grommet and brake booster when the check valve is inserted in the seal. The compression of seal is about 30% so comments about the size problem excreta are not valid. The real sealing problem in this area is caused by containments on the sealing surface or poor surface finish on the brake booster with latter not being that common.

The most important step in replacing the seal is to clean the brake booster sealing surfaces with Isotropic alcohol and make sure you do a good job. The reason you need to do this is all seal material will leave a film on the sealing surface due to material loss which can causes leaks ( happens with any vacuum system). If you miss this step and you are likely to have problems.

There are two solutions to this problem. I would recommend using silicon grease (or vacuum grease). Apply a thin film (.05 – 0.1 mm thick) on grease inside the grommet sealing grove (3 surfaces), the lead-in chamfer of the seal to aid insertion, and the inside diameter of the seal where the hose barb is inserted. This is well know and typically done when working with any vacuum sealing system. The alternative is to use a silicon RTV sealant. Use only a thin film (0.05 mm thick) of RTV on the radial part of the seal grommet grove. Once the seal is inserted the silicon will spread on all sealing surfaces. If you use to much you risk getting pieces of the RTV getting sucked into vacuum pump. I would not recommend the RTV method unless there is no choice.

If you have replaced the check valve hose assembly and experience random hard brake pedal then you likely have a slow leak somewhere else in the system. The check valve in the brake booster is designed to holder higher vacuum than the rest of the system when the car is turned off. In other word, if you turn off the car then you should be holding about 28 hg in the brake booster and 16 hg past the check valve. If there is a leak past the check valve and the system leaks down to atmosphere pressure, then the check valve in brake booster will leak down significantly and you will have various degrees of a hard brake pedal. If you do have a slow leak in your system you will typically hear the waste gate rattle at start up that last more than 2 seconds since the vacuum has leaked done to atmosphere pressure and it take a while for the system build up a vacuum which can take 5-20 seconds. There should be no rattle of the waste gates at start up if the system is healthy.

To check for leaks you need a hand vacuum pump and gauge then you will be able to identify which component is the problem. Check all tubing individually for leaks. The list below is typical issues with this car:

• Two vacuum canisters. They should hold 30 hg more than hour when tested discretely.

• The two vacuum lines behind the oil filter housing will leak after time (replace every 3-4 years). Mine had a very slow leak.

• The waste gate pressure converters tend to leak randomly on pre 09 cars. Mine needed to replace although I had no issues with the car.

In my case, I had to replace 50% vacuum lines, check valve hose assembly + seal and the pressure coveters to fix the hard brake pedal problem.
Last edited by Orb; 11-08-2013 at 09:27 AM.
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  #10  
By Built My Way on 11-09-2013, 08:37 AM
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Quote:
Originally Posted by Orb View Post
This is a good post in this section but needs some clarifications. If you replacing the check valve house assembly it will be a good idea to replace the seal. The method from “PhaseP” works well if you are creative in rigging up an installation tool for the seal.

There is nothing wrong with the seal design but a better design could have been used. The sealing takes place in the radial grove of the grommet and brake booster when the check valve is inserted in the seal. The compression of seal is about 30% so comments about the size problem excreta are not valid. The real sealing problem in this area is caused by containments on the sealing surface or poor surface finish on the brake booster with latter not being that common.

The most important step in replacing the seal is to clean the brake booster sealing surfaces with Isotropic alcohol and make sure you do a good job. The reason you need to do this is all seal material will leave a film on the sealing surface due to material loss which can causes leaks ( happens with any vacuum system). If you miss this step and you are likely to have problems.

There are two solutions to this problem. I would recommend using silicon grease (or vacuum grease). Apply a thin film (.05 – 0.1 mm thick) on grease inside the grommet sealing grove (3 surfaces), the lead-in chamfer of the seal to aid insertion, and the inside diameter of the seal where the hose barb is inserted. This is well know and typically done when working with any vacuum sealing system. The alternative is to use a silicon RTV sealant. Use only a thin film (0.05 mm thick) of RTV on the radial part of the seal grommet grove. Once the seal is inserted the silicon will spread on all sealing surfaces. If you use to much you risk getting pieces of the RTV getting sucked into vacuum pump. I would not recommend the RTV method unless there is no choice.

If you have replaced the check valve hose assembly and experience random hard brake pedal then you likely have a slow leak somewhere else in the system. The check valve in the brake booster is designed to holder higher vacuum than the rest of the system when the car is turned off. In other word, if you turn off the car then you should be holding about 28 hg in the brake booster and 16 hg past the check valve. If there is a leak past the check valve and the system leaks down to atmosphere pressure, then the check valve in brake booster will leak down significantly and you will have various degrees of a hard brake pedal. If you do have a slow leak in your system you will typically hear the waste gate rattle at start up that last more than 2 seconds since the vacuum has leaked done to atmosphere pressure and it take a while for the system build up a vacuum which can take 5-20 seconds. There should be no rattle of the waste gates at start up if the system is healthy.

To check for leaks you need a hand vacuum pump and gauge then you will be able to identify which component is the problem. Check all tubing individually for leaks. The list below is typical issues with this car:

• Two vacuum canisters. They should hold 30 hg more than hour when tested discretely.

• The two vacuum lines behind the oil filter housing will leak after time (replace every 3-4 years). Mine had a very slow leak.

• The waste gate pressure converters tend to leak randomly on pre 09 cars. Mine needed to replace although I had no issues with the car.

In my case, I had to replace 50% vacuum lines, check valve hose assembly + seal and the pressure coveters to fix the hard brake pedal problem.
Wow! Much of what you said just doesn’t make sense. Contaminants will not factor in as long as there is a tight seal. If contaminant build up is an issue here, it’s only because an under designed (loose fitting) grommet has allowed that kind of environment to exist. Your quick fix solution by applying grease or RTV sealant defeats your own argument. For this application, these products should not have to be used if the seal is tight. I’ve never had to do this on any of my other my other vehicles that I’ve owned through the years. Your suggestion of using these products is an admission that there is a problem with the rubber grommet. You also mentioned brake booster surface finish. The hard brake issue on these vehicles appears later on during ownership. A poor factory finish would have caused this problem to occur much sooner. You stated something about a 30% seal compression without any supporting data and then promptly used this to shoot down my argument. Not very compelling I have to say. Your compression figure is irrelevant especially if you haven’t taken sample measurements of any kind. The Test portion of the DIY performed on my vehicle proves that the slightest displacement of the grommet can break the vacuum within the housing. Unless the area of concern is remedied by a properly sized grommet being compressed by the barbed check valve forming a proper seal between its “radial” groove and the opening in the brake boost housing, this problem will continue to exist. I contend that the circumferential tolerance of the groove is just under which is minimally acceptable which is why only a few vehicles have experienced the leakage. Temperature variations over time, vibration and grommet shrinkage are more likely the factors which aid in initiating the problem, not contaminants or booster surface condition.

Again I have to call you out on your comments about leaks in other parts of the system that rely on a vacuum and how they can affect brake booster vacuum. Your arguments on this are basic nonsense. The check valve at the brake booster is designed to hold the 28hg no matter what happens in the event of vacuum loss in other parts of the system of lines otherwise the entire braking system would be compromised in the event of a catastrophic engine malfunction. A proper check valve (with proper rubber grommet) will continue to maintain the vacuum in the booster even with atmospheric pressure at sea level in the vacuum system lines.

I can’t imagine why someone would try to blame waste gate rattle for brake vacuum loss. IDK, maybe there’s some cryptic details that I’m missing in here.
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  #11  
By Orb on 11-09-2013, 02:09 PM
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Quote:
Originally Posted by Built My Way View Post
Wow! Much of what you said just doesn’t make sense. Contaminants will not factor in as long as there is a tight seal. If contaminant build up is an issue here, it’s only because an under designed (loose fitting) grommet has allowed that kind of environment to exist. Your quick fix solution by applying grease or RTV sealant defeats your own argument. For this application, these products should not have to be used if the seal is tight. I’ve never had to do this on any of my other my other vehicles that I’ve owned through the years. Your suggestion of using these products is an admission that there is a problem with the rubber grommet. You also mentioned brake booster surface finish. The hard brake issue on these vehicles appears later on during ownership. A poor factory finish would have caused this problem to occur much sooner. You stated something about a 30% seal compression without any supporting data and then promptly used this to shoot down my argument. Not very compelling I have to say. Your compression figure is irrelevant especially if you haven’t taken sample measurements of any kind. The Test portion of the DIY performed on my vehicle proves that the slightest displacement of the grommet can break the vacuum within the housing. Unless the area of concern is remedied by a properly sized grommet being compressed by the barbed check valve forming a proper seal between its “radial” groove and the opening in the brake boost housing, this problem will continue to exist. I contend that the circumferential tolerance of the groove is just under which is minimally acceptable which is why only a few vehicles have experienced the leakage. Temperature variations over time, vibration and grommet shrinkage are more likely the factors which aid in initiating the problem, not contaminants or booster surface condition.

Again I have to call you out on your comments about leaks in other parts of the system that rely on a vacuum and how they can affect brake booster vacuum. Your arguments on this are basic nonsense. The check valve at the brake booster is designed to hold the 28hg no matter what happens in the event of vacuum loss in other parts of the system of lines otherwise the entire braking system would be compromised in the event of a catastrophic engine malfunction. A proper check valve (with proper rubber grommet) will continue to maintain the vacuum in the booster even with atmospheric pressure at sea level in the vacuum system lines.

I can’t imagine why someone would try to blame waste gate rattle for brake vacuum loss. IDK, maybe there’s some cryptic details that I’m missing in here.
It is fairly obvious you have something to defend and your point of view is an attack based on ego. The comments I made are based on 20+ years as a professional mechanical engineer. I am not going to debate what I said as this would be like a two year old saying the sky is red and I saying it is blue. In short, your basic understating of material sciences is non existent and would go as far as saying internet folklore from what you’re saying. For reference, you can look up “vacuum seal design” and use the Parker site as reference as it has all the information and charts one would need. As for the other comment, I am not sure what to say other than you’re not smart enough to understand a basic mechanical system. If you actually had a specific question I certainly would have answered it but you don’t.

The information you provided is useful and appreciated but it has been expanded on as well. People can have the free will to choose what they want to proceed with. There is information that will work everyone. You need to grow up and learn that other points of view are okay and as whole as they will help people with this problem. The point of the thread is to help others or do you have your head to far up your ass to see this.

Feel free to write more comments as it is your choice but not going to respond. I understand why I no longer post here anymore LOL.
Last edited by Orb; 11-09-2013 at 03:39 PM.
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  #12  
By Built My Way on 11-09-2013, 03:46 PM
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Quote:
Originally Posted by Orb View Post
If fairly obvious you have something to defend and your point of view is an attack based on ego. The comments I made are based on 20+ years as a professional mechanical engineer. I am not going to debate what I said as this would be like a two year old saying the sky is red and I saying it is blue. In short, your basic understating of material sciences is no existent and would go as far as saying internet folklore from what you’re saying. For reference, you can look up “vacuum seal design” and use the Parker site as reference as it has all the information and charts one would need. As for the other comment, I am not sure what to say other than you’re not smart enough to understand a basic mechanical system. If you actually had a specific question I certainly would have answered it but you don’t.

The information you provided is useful and appreciated but it has been expanded on as well. People can have the free will to choose what they what to proceed with. There is information that will work everyone. You need to grow up and learn that other points of view are okay and as whole as they will help people with this problem. The point of the thread is to help others or do you have your head to far up your ass to see this.

Feel free to write more comments as it is your choice but not going to respond. I understand why I no longer post here anymore LOL.
Jeez, I feel like I'm being trolled here. Anyway, I'm sorry if you felt offended by my reply. I really don't find satisfaction in attacking people. I simply correct blatant inaccuracies, especially those that involve something that I've taken time to research. It's not too often you see on this forum, people doing what you just did. Hi-jacking a DIY with misinformation is not providing a point of view nor is it contributing in a helpful way. I couldn't let your comments go unchecked. You must know what it's like, being an engineer and all. If we see a wrong, we correct it. Yes, I'm a mechanical engineer as well... brother. 25+ years by the way but whose counting right?
I hope that you will to read this so that you might learn something about tact and the nuances of positive feedback. And there's no need for name calling here. Again I apologize if I've hurt your feelings.
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  #13  
By Orb on 01-03-2014, 06:21 AM
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Quote:
Originally Posted by Built My Way View Post
Jeez, I feel like I'm being trolled here. Anyway, I'm sorry if you felt offended by my reply. I really don't find satisfaction in attacking people. I simply correct blatant inaccuracies, especially those that involve something that I've taken time to research. It's not too often you see on this forum, people doing what you just did. Hi-jacking a DIY with misinformation is not providing a point of view nor is it contributing in a helpful way. I couldn't let your comments go unchecked. You must know what it's like, being an engineer and all. If we see a wrong, we correct it. Yes, I'm a mechanical engineer as well... brother. 25+ years by the way but whose counting right?
I hope that you will to read this so that you might learn something about tact and the nuances of positive feedback. And there's no need for name calling here. Again I apologize if I've hurt your feelings.
What you said is actually a reflection of your behavior which is very transparent. Your projected BS is noted but you can have it back. Like I said, your basic mechanical understanding is nonexistent. Pushing the seal with a screw driver to create a leak and thinking it means something is the obvious clue. …what the hell are you thinking? If you are actually an engineer you would have measured the parts in question. The fact is, you did little real research, made a bunch of assumptions, and validated none of them.

You are stating that BMW has a design issue with the seal and you’re not presenting any evidence. The seal was checked and there is no issue with the design as one would expect. You suggest some proof so please provide the details and explanation since you initiated the findings. You created a problem and know defending it to the point of lying.

Considering that you can replace the seal with long forceps and a screw driver makes you DYI is pointless although the fix is still valid.
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  #14  
By Built My Way on 01-06-2014, 11:07 AM
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Originally Posted by Orb View Post
Feel free to write more comments as it is your choice but not going to respond.
I thought you were done? Guess you couldn't stand me having the last word huh.
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