[GeorgeKLT]

Hi all,

I went ahead and upgraded the front brakes(pads, rotors, calipers, carriers, disc protections) on my e90 318d prod. year 2009

from the 300mm x24mm stock discs now it has the same setup of a 335d namely 348mm x 30mm

Should I change the brake master cylinder as well, same questions applies to brake booster. Below you can see the only difference between the master cylinders.

stock brake master cylinder
cylinder bore 1 [mm]:22,20
cylinder bore 2 [mm]: 23,81

335d brake master cylinder
cylinder bore 1 [mm]:22,20
cylinder bore 2 [mm]: 25,40

For brake booster I was not able to find any technical details, so I was not able to see the difference except they have different Part Numbers.

Please let me know your thoughts, since only the front brakes have been upgraded would you leave it as it is or would you change brake master cylinder/brake booster and perform coding as well.

Thanks.

[Silver Streek]

Yes I would upgrade the master cylinder too, this should always match the calipers. The bigger calipers will have a bigger piston requiring more brake fluid so you need to be able to provide that fluid.

I'm sure you could get away without changing it but you won't get the benefit of the bigger brakes.

Just out of interest why go with 335d brakes on a 318d, wouldnt 330d brakes have been a better choice?

[GeorgeKLT]

Thank you for your reply.

I was hoping to get away without replacing the master cylinder but you got me wondering.

Initially I wanted the 330d brakes but I found an offer for 335d brakes that I couldn't refuse.

[therealdb1]

Yes you should change the master cylinder to match the calipers for the reason Silver Streak has given but I wouldn't think the servo booster will make much difference unless you need a 335 one to match the new master cylinder fixings.

The booster will only change the effort required to push the pedal not the amount of braking available so if the master cylinder and calipers are properly matched I would not expect the "boost" to be much different.

[Andystobbs]

I've had 335d brakes on my 320d for nearly a year without changing the servo or master cylinder.

I have the 348s up front and big brakes at the back too, 315mm is it?

Edit. Rears are 336mm. Difficult upgrade but well worth the look to complement the larger fronts.

Car stops just fine.

[Andystobbs]

Just to add, the brakes are still well capable of overcoming the limit of traction from the tyres. So apart from reducing pedal travel I can't see the point.

[GeorgeKLT]

Andy, funny you should mention 320d.

I did check the part numbers before posting and your 320d(e90) has the same part number as 335d for the brake master cylinder namely 34336785664

Probably that is why you don't feel the need to upgrade your master cylinder.

Mine(318d), on the other hand, has a "weaker" master cylinder Part Number 34336785662.

[Andystobbs]

Originally Posted by therealdb1

Yes you should change the master cylinder to match the calipers for the reason Silver Streak has given but I wouldn't think the servo booster will make much difference unless you need a 335 one to match the new master cylinder fixings.

The booster will only change the effort required to push the pedal not the amount of braking available so if the master cylinder and calipers are properly matched I would not expect the "boost" to be much different.

The booster (servo) is likely to be more powerful to compensate for the loss in advantage from a larger master cylinder.

OP: I must admit I'd never checked my master cylinder part number. My VIN in realoem gives 34336785665 as my master cylinder.

[david in germany]

There is no need to change out the master cylinder.. just code the car to add +spbr. Nothing else.

[Andystobbs]

Originally Posted by david in germany

There is no need to change out the master cylinder.. just code the car to add +spbr. Nothing else.

Not trying to rock the boat at all. I was very grateful for the advice given to me when I was asking about the nuances of adding bigger brakes.

David in germany was a responder in the thread I posted in and advised I code SPBR. At the time I had the wrong DSC module - electrics only, not hydraulics - after bricking my original during software update. I sourced a module with correct part number but the software was different and consequently NCS wouldn't access it. Fearful of another failed programming session, and another bricked module I never coded SPBR and still maintain the car is fine.

Some people say the addition of SPBR adds feel to the brakes. Personally I'd rather not have them so sharp that I'm in danger of going through the windscreen.


I have since successfully programmed my DSC but still left off the SPBR option.

I'm about to retrofit (around Christmas time hopefully) a 6 cylinder DSC complete - electrics and hydraulics - in readiness for active cruise control. So we'll see if that changes anything. Technically shouldn't as donor car is a 330d.

[Silver Streek]

Originally Posted by Andystobbs

Not trying to rock the boat at all. I was very grateful for the advice given to me when I was asking about the nuances of adding bigger brakes.

David in germany was a responder in the thread I posted in and advised I code SPBR. At the time I had the wrong DSC module - electrics only, not hydraulics - after bricking my original during software update. I sourced a module with correct part number but the software was different and consequently NCS wouldn't access it. Fearful of another failed programming session, and another bricked module I never coded SPBR and still maintain the car is fine.

Some people say the addition of SPBR adds feel to the brakes. Personally I'd rather not have them so sharp that I'm in danger of going through the windscreen.


I have since successfully programmed my DSC but still left off the SPBR option.

I'm about to retrofit (around Christmas time hopefully) a 6 cylinder DSC complete - electrics and hydraulics - in readiness for active cruise control. So we'll see if that changes anything. Technically shouldn't as donor car is a 330d.

Sounds like an interesting project, keep us posted how it goes.

[GeorgeKLT]

Originally Posted by Andystobbs

The booster (servo) is likely to be more powerful to compensate for the loss in advantage from a larger master cylinder.

OP: I must admit I'd never checked my master cylinder part number. My VIN in realoem gives 34336785665 as my master cylinder.

You are right about the Part Number 34336785665 for the MC if you search with your VIN.

If you do like I did and search on realoem by series, body, model, market production year, engine then you will find the e90 320d up to 335d will have the same master cylinder, PN 34336785664

Let me see if I understood, it's wrong of me to replace only the master cylinder without changing the brake booster, is that what you are saying?

[GeorgeKLT]

Originally Posted by david in germany

There is no need to change out the master cylinder.. just code the car to add +spbr. Nothing else.

So coding the car with +spbr would compensate for the weaker master cylinder on my 318d?

[Andystobbs]

Originally Posted by GeorgeKLT

You are right about the Part Number 34336785665 for the MC if you search with your VIN.

If you do like I did and search on realoem by series, body, model, market production year, engine then you will find the e90 320d up to 335d will have the same master cylinder, PN 34336785664

Let me see if I understood, it's wrong of me to replace only the master cylinder without changing the brake booster, is that what you are saying?

No, I personally wouldn't worry about changing non of it, some of it, or all of it. So long as the car stops and you're happy with the feel of the pedal. Leave it if you're not bothered.

[Silver Streek]

Originally Posted by Andystobbs

No, I personally wouldn't worry about changing non of it, some of it, or all of it. So long as the car stops and you're happy with the feel of the pedal. Leave it if you're not bothered.

I hear what you saying but i think you should consider the output of a smaller master cylinder paired up with larger brake calipers when your pads get low. If like most people you wear your pads till they get thin then you need to supply those bigger pistons with a fair bit more fluid. It could happen that to get full braking with worn down pads you may have to double pump the brake pedal. After all if the smaller master cylinder can feed those bigger pistons why did BMW put a bigger more expensive part on the bigger engines cars with bigger brakes?

[Andystobbs]

Originally Posted by Silver Streek

I hear what you saying but i think you should consider the output of a smaller master cylinder paired up with larger brake calipers when your pads get low. If like most people you wear your pads till they get thin then you need to supply those bigger pistons with a fair bit more fluid. It could happen that to get full braking with worn down pads you may have to double pump the brake pedal. After all if the smaller master cylinder can feed those bigger pistons why did BMW put a bigger more expensive part on the bigger engines cars with bigger brakes?

Don't see how this is applicable. The distance between disc and pad in the relaxed state is always the same. Regardless of pad wear. The amount of fluid required to close the gap will always be the same. That is why the piston constantly increments out of the caliper as pad material is worn away. The reservoir provides the extra fluid as caliper piston progresses out.

[Silver Streek]

Originally Posted by Andystobbs

Don't see how this is applicable. The distance between disc and pad in the relaxed state is always the same. Regardless of pad wear. The amount of fluid required to close the gap will always be the same. That is why the piston constantly increments out of the caliper as pad material is worn away. The reservoir provides the extra fluid as caliper piston progresses out.

I agree in theory, but as the pistons push out as the pad wears, when the pads get really worn the pistons do sometimes suck back into the caliper housing. No idea why I'm a mechanical design engineer not a hydraulics expert.

Ever noticed how your pedal travel increases when your pads get towards the end of their life?

[Andystobbs]

I can't say I've ever experienced that. I've always attributed any loss of feel to the generous amount of rust that seems present on any brake disc by the time one set of pads has been consumed.

It'd be interesting to do some calculations on how much caliper piston movement is generated by a full pedal stroke. For all combinations of M/C vs Calipers.

[Silver Streek]

Would be fairly easy to do, you could do a rough calculation as to what force is exerted by the piston onto the brake pad too with the master cylinder/caliper dimensions. You would have to make an assumption of the force applied to the brake pedal though (taking into account the additional force added by the servo)

But I think that's far too technical for this forum 😂

I definitely have more brake travel with this E91 with warn pads, less so that with my E46 tho, that was much worse.

Thinking about it, the difference in size in the diameter of the master cylinder would actually have much more of a profound effect on the hydraulic force created by the master cylinder compared with the extra fluid flow. There's a direct relationship between the surface area of the piston where the hydraulic fluid acts to its force output. Basically the greater the surface area the fluid has to act on the greater force will be produced by the caliper piston.

Hence why you can hand pump a small bottle jack which will multiply your arm power enough to be able to lift a car just with two different sized pistons.

So a bigger master cylinder would create more fluid pressure acting on the caliper piston resulting in a bigger force applied to the brake pad.

Anyhow the proofs in the pudding, if you've fitted big brakes to the smaller master cylinder and it works then that's it, it works. Just bear in mind it could be even better if you used the bigger master cylinder.

[Andystobbs]

You have your hydraulics backwards. The smaller the master cylinder relative to the slave cylinder the greater the multiplication in force.

You'll lose stroke because the smaller master cylinder displaces less fluid but the force available at the slave will be greater with the smaller master cylinder for the same force applied to it.

[GeorgeKLT]

Thank you for taking the time to help me out.

I will go the extra mile and order a new ATE brake master cylinder that matches the bmw code for the bigger MC.
I will come back and let you know the results.

Cheers

[Silver Streek]

Originally Posted by Andystobbs

You have your hydraulics backwards. The smaller the master cylinder relative to the slave cylinder the greater the multiplication in force.

You'll lose stroke because the smaller master cylinder displaces less fluid but the force available at the slave will be greater with the smaller master cylinder for the same force applied to it.

Yes you are quite right Andy, I am thinking about it backwards . Good job I dont work in hydraulics. I'm used to big lumps of metal in transport.