[windymissile]

I take responsibility for the work I do on my car. You will need to do the same.

This is a basic DIY for people looking to swap their Differential inside the 335i Auto, small pumpkin.

A reference first. And a thanks to Birds Automotive. ( http://www.birdsauto.com/ )
Please make sure you read this before going any further.
http://www.birdsauto.com/sites/defau...2014n%20v3.pdf

Loads of really important information in this one simple document.

Firstly, 24 hours before the diff is due to be fitted, put in in the freezer.


As you can see, the output shaft outer diameter will shrink just enough to allow you to slide on the bearing inner race without too much trouble.


Next you're going to have to get out the old Pumpkin.
I wore safety glasses. I suggest you do the same. Rust will be raining down on you from the fasteners. It's no fun when it goes in your eye.. http://www.ebay.co.uk/itm/Industrial...item53f7385787
I jacked up the rear from the rear subframe with a tall jack. I then sat it down on axle stands and put my winter wheels under the sills for extra security. Always chock the front wheels to prevent the car moving! You will need at least 18". Once under, give all the connecting fasteners a soak in good Ol' WD40.


To disconnect the input shaft (prop), turn the 50mm hex *GREEN ARROW* nut anti-clockwise (looking from rear). Do not turn the BI-Hex nut *RED ARROW*

You will need a special tool for the 50mm nut. It's just a skinny spanner. I had one made. It can be seen here amongst other tools.



Next you will need to disconnect the output shafts. For this you will need a E12 torx bit. Not in every socket set but available from most good tool suppliers. UK guys can find them in Halfords.


Next the front two mounting bolts will need to be removed. These are threaded through the diff housing, so after running the nut off the rear, the bolts will need to be wound out from the front. You can remove the exhaust and the heat sheild to make this easier. I just released the shield a little and used a long 1/2" extension to get at it from behind the prop shaft. You probably want to leave them just on a 1/2 thread while you get the weight.


Now the diff is just held in by the rear bolt. I used the jack to support the weight of the diff while I removed this. Once all the fasteners are out, gravity will help you and the diff should drop clear of the car. I brought it down output shaft first. *WARNING!* The diff is heavy! Approx 40KG!


Hump it up onto the bench and crack the rear cover off to drain the old oil. Clean the 2 mating faces.


Now you will need to pull off the 2 output shafts. I used a piece of alloy plate I had lying about from an old job and a slide hammer. Drilling the plate to take the original output shaft fasteners and the hammer.


The old seals will be rusted in. So snip them from the inside and twist the material up to break them away from the casing just enough to get a screwdriver in behind them to work them out.



This will expose the bearings and retaining clips/shims.
(No pics, sorry)

I now checked the backlash before stripping out the old bearings and diff.
Set the DTI up by attaching it to the diff casing with the magnetic base. Then carefully position the needle on one of the pinion wheel teeth and lock it in position. It doesn't have to be at zero. (This can take quite a bit of fiddling).
Slide the output shaft back in loosely so you can apply drive to the diff. By gently rocking 'to n' fro' you will feel the drive mating against the pinion wheel. This is the backlash. There are some better pictures and limits stated in the Birds documentation I quoted at the start of the thread.





If this backlash figure is within limits and you have no diff whine, you should be able to reuse your old bearings. I replaced mine regardless, as they had done 80k.

Getting the bearing retaining clips out requires a real knack. I used some big swan neck pliers.

You will need to squeeze the ring together while trying to wriggle it out of the housing. It's a real pain in the ass. Be careful, as you do NOT want to damage these clip rings!
*These retaining clips set the backlash and are machined to fit your individual pumpkin and bearings. Left it left and right is right! Do not mix them up! they will need to go back into the side they came from! If you are reusing the bearings, these are to go back in the same side too!! * Refer to the Birds documentation for pictures of the retaining clips. (I had my hands full).

Once the retaining rings are out the outer bearing race will drop through and the diff can be removed.
Once the diff is out, I took the housing outside and gave it a real good scrub with a wire brush to get all the loose surface rust off. When you start the rebuild you will need a sterile environment. The cleaner the housing is the easier it is to maintain this environment.
It's important that the housing output shaft internal faces are clean. Don't go mad scraping away any material, but you will need to make sure all the rust is removed. When you remove the seals you will see what I mean.

CLEANLINESS IS IMPERATIVE!! You do not want anything swimming around in the diff thats not supposed to be there. Not even the tiniest speck of rust.

When you have the diff out you will end up with this on the bench.


I don't have a big bench vice at home so I had to improvise with some big G clamps and some 2x2". It is really important you do not damage the ring gear teeth while removing it. So be really careful how you hold it.


The ring gear is held onto the Diff with 10 bolts. They are tight and thread locked into position! I had to use a big breaker-bar to crack them off.
Once all the bolts are out you will end up with this. The ring gear is what you need. The old diff could make a nice door stop.


Now get your new MFactory diff from the freezer and slide your OEM ring gear over it. Using the original bolts (cleaned) and high strength thread lock you will need to torque them to the specs in the Birds documentation. 100Nm+. Not easy, as the diff isn't easy to hold. You want to pull it down symmetrically so it's good practice to tighten opposite bolts.


Once this is done, slide your new bearings on and give everything a good clean. You may need to use a large socket to drive the bearings onto the output shaft, if like me, you don't have a press. Just go real steady as you do not want to damage the bearing. If it's a little tight, just bring the bearing to the boil in a pan of water. But if the diff has been in the freezer for 24 hours it shouldn't be a problem.
* If you are using your old bearings, you will need to use a bearing puller to remove the old race from the old diff. Then reinstall this on the MFactory diff. Pics in the Birds documentation *


Now you will need to reassemble the diff into the casing. Make sure the retaining clips go back in the same side they came from. The new bearings are supposed to be the same width as the OEM but I found that mine were 0.1mm wider. Giving me zero backlash, and I could physically feel the crown wheel binding against the pinion. So I had to 're-shim'. I machined down my original shim to give me the required backlash. This was a constant trial and error process that took me most of the evening. Taking 0.01mm off every time. Then re-assembling and checking backlash.
Taking material off is always easier than putting it back on. So make sure you don't go too far.
If you need to add shims as your backlash is too much. You should speak with MFactory. But my option would be to add shims under the bearing. This will mean you will have to pull the bearing off the diff again.
http://www.springfasteners.co.uk/pro...0_1mm_din_988/
When finished, you will have this in front of you!


Make sure you have cleaned everything and checked in the housing to make sure it is spotless! Then apply the new liquid gasket to the rear half of the casing and bolt it back up.


Now replace the output shaft seals and slide the output shafts back in until the lock ring (there is a new one in with the seal) engages.


I put 1L of oil in while it was on the bench to make life easier and to check for leaks before I installed. If this leaks you will have to remove the whole thing again to re-do the seal!!


Installation is simply the opposite of removal! Although you won't have gravity to help you get it back in!
I balanced the diff on the jack and slowly raised it into position. Back end first and engaging the prop shaft while it was on it's way up. Once it's high enough I slid the rear bolt through the wrong way, just to hold it up there while I engaged the front 2. Once the fronts are in, remove the rear and put it in the correct way round.
It's a bit of an awkward job on your own on the floor. If you have access to ramps and a transmission jack it would be much easier.
Connect the output shafts and the input shaft. Check all fasteners are tight and fill the diff until the oil starts to drip from the fill port. Should hold about 1.2L (You will have already put 1L in)

Drive real gingerly for the first 10 mins. Making sure there are no odd noises coming from the rear. Doing many 3 point turns and tight maneuvers. Once everything seems ok, slowly start applying more and more power until you are confident it's all working as it should be. Then give it some abuse.

I may have missed out some steps or detail. So if there are any questions please ask them in this thread and I will do my best to answer them.

It's on the limits for what's capable as a DIY. But not impossible for someone who knows how to spanner..

Good luck!

WM

[windymissile]

Reserved.

WM

[Phil325i]

Nice guide! Seeing the diff stripped, it's scary how little fluid it contains. Apparently BMW have been progressively reducing the size of their diffs over the years (to save weight/cost?) and introduced some internal parts made of plastic.

[M-Steep]

Originally Posted by Phil325i

Nice guide! Seeing the diff stripped, it's scary how little fluid it contains. Apparently BMW have been progressively reducing the size of their diffs over the years (to save weight/cost?) and introduced some internal parts made of plastic.

No plastic.

[AWSAWS]

Are you a mechanic or engineer WM? I could never imagine a regular person doing this kind of thing. Not having the tools for one thing.

Very impressive. How did you lift and position the pumpkin back in to place at 40kgs???

[Dave2013]

cant wait for the next update.....massive thanks for posting this up WM.

Dave

[windymissile]

Originally Posted by AWSAWS

Are you a mechanic or engineer WM? I could never imagine a regular person doing this kind of thing. Not having the tools for one thing.

Very impressive. How did you lift and position the pumpkin back in to place at 40kgs???

I did a 5 year aircraft technical apprenticeship. And I have worked on some pretty impressive machinery. Since moved on to work with offshore renewable energy generation. I've been on the spanners since as young as I can remember, so this kind of thing comes naturally to me.

Getting it back in on my own was a right pig of a job! It only goes in one way and it took some fine balancing on the trolly jack, which I was operating with my leg while trying to get the bolts in!

Originally Posted by Dave2013

cant wait for the next update.....massive thanks for posting this up WM.

Dave

No worries Dave. I hope it is of use when you come to get yours in!

WM

[windymissile]

Updated.

WM

[zltm089]

Respect!

[mob17]

Very impressive mate! Do you have a unit you work from or all on driveway?

There's someone else on the forum who also did this but using a wavetrac. He also works in the aircraft engineering industry!

[windymissile]

Cheers guys.
I have a garage but no room for the car in there as it's full of work stuff, tools and a motorbike. There is a work bench though. All the work on the car was done on the driveway.
WM

[MFactory]

Very nice writeup, thank you

[windymissile]

Originally Posted by MFactory

Very nice writeup, thank you

No worries, Stephen.
I have about 700 miles on it so far. It's a beautifully simple piece of kit.

I hope you didn't mind me directing people to you in regards of the shims.

WM

[MFactory]

Of course not

[windymissile]

Originally Posted by MFactory

Of course not

Do you think the shims I linked to would be suitable for removing excess backlash? By positioning under the bearing?
http://www.springfasteners.co.uk/pro...0_1mm_din_988/

WM

[M-Steep]

Originally Posted by windymissile

Cheers guys.
I have a garage but no room for the car in there as it's full of work stuff, tools and a motorbike. There is a work bench though. All the work on the car was done on the driveway.
WM

Nice work, WM. And thanks again for the good wishes. I got my LSD in with the roller bearings. With my calipers (0.001" readout), they measured dead-on same thickness (stack) as the ball bearings, but cost me -.0005" backlash, per dial guage, which left me at .0025", so I declared victory and buttoned things back up.

Got it bolted back in with the help of a friend. I LOL'd at your "used my leg to work the jack", because I knew exactly what you were talkin about. I contemplated same, but was saved by a timely visit from my buddy. Even then, it required copious profanity and jostling.

[AWSAWS]

Originally Posted by windymissile

No worries, Stephen.
I have about 700 miles on it so far. It's a beautifully simple piece of kit.

I hope you didn't mind me directing people to you in regards of the shims.

WM

700 miles! You don't hang about mate.

[windymissile]

Originally Posted by M-Steep

Nice work, WM. And thanks again for the good wishes. I got my LSD in with the roller bearings. With my calipers (0.001" readout), they measured dead-on same thickness (stack) as the rollers, but cost me -.0005" backlash, per dial guage, which left me at .0025", so I declared victory and buttoned things back up.

Got it bolted back in with the help of a friend. I LOL'd at your "used my leg to work the jack", because I knew exactly what you were talkin about. I contemplated same, but was saved by a timely visit from my buddy. Even then, it required copious profanity and jostling.

Glad it's all sorted. There was a lot of swearing and scraped knuckles getting it back in!

WM

[windymissile]

Originally Posted by AWSAWS

700 miles! You don't hang about mate.

Yeah. I don't mind putting the miles on it! A couple of long trips. Most of them done late at night on deserted motorways, so I can test it fully.

WM

[windymissile]

Originally Posted by M-Steep

Nice work, WM. And thanks again for the good wishes. I got my LSD in with the roller bearings. With my calipers (0.001" readout), they measured dead-on same thickness (stack) as the rollers, but cost me -.0005" backlash, per dial guage, which left me at .0025", so I declared victory and buttoned things back up.

Got it bolted back in with the help of a friend. I LOL'd at your "used my leg to work the jack", because I knew exactly what you were talkin about. I contemplated same, but was saved by a timely visit from my buddy. Even then, it required copious profanity and jostling.

How have the first few days with it been?
Don't forget to re-check the oil level.
WM

[M-Steep]

Just got completely finished up and out on road last night for maiden voyage. Only ~15 miles, just within neighborhood.

Lots of turning, starting, stopping. Max speeds of only ~40 mph. Couple of modestly brisk exits from turns and starts from standstill.

So not too much to judge by yet, but all seems solid. No clunking, no hint of slip or DCS intrusion under moderate accelerations. No parts fell off the car!

I also replaced diff and subframe bushings with AKG poly (95A). I can hear bit of whine if I try, but really quite slight and not unpleasant at all.

Need rear tires and alignment - that happens tomorrow, and then the fun shall truly commence.

Thanks again for the great info shared.

P.S. Thanks for reminder on oil level check - I'll recheck this weekend.

[mob17]

M-Steep. You noticed a slightly firmer rear with the stiffer subframe bushings?

I don't know whether to go for M3 ones or solid aluminium...

Anyways congrats i can't wait to get one in mine!