Looking for a 3.90 to 4.10 diff.

[maupineda]

Originally Posted by grannyknot

Just want to clarify again what is being done to this Z4M LSD diff.
New bearings and seals all around, new clutch pack and a change of gear ratio from stock 3.60:1 to 3.90:1
First 2 pics are the old ring and pinion, last 2 pics are the new ring and pinion.
If you can't read it the old pinion specs are, XMK3628 10 25 +20288

What defines the matching set are the 4 letters

AUGE for your new set
PLUS for your old set (PLUS is just a funny coincidence)

+1 is the hundreds of millimeters, in this case, on the plus side.

[Westersund]

Usually you don't have to change the pinion shim, you can adjust the backlash and gear pattern with the side shims only. Just did my rear axle in the E46 M3 (RSX ramp/clutch style diff and BMW Motorsport 4.45 gearing) because the previous owner is a twat, 3 crown wheel bolts was lost and 2 more was coming undone. Pre-load in the pinion bearings was set to 1 Nm and 0,8 Nm in the side bearings, BMW recommend ridiculously high 2,5 Nm in the pinion bearings and about 2 Nm in the side bearings. Backlash was measured in 3 different places on the crown wheel and turned out to 0,05, 0,08 and 0,14 mm, the BMW recommended backlash is 0,05-0,08 but that couldn't be done in my case (rather have a little more backlash rather than less to have sufficient room for lubrication).

Most importantly, don't forget to use Loctite 270 when installing the crown wheel bolts.

[maupineda]

Originally Posted by Westersund

Usually you don't have to change the pinion shim, you can adjust the backlash and gear pattern with the side shims only. Just did my rear axle in the E46 M3 (RSX ramp/clutch style diff and BMW Motorsport 4.45 gearing) because the previous owner is a twat, 3 crown wheel bolts was lost and 2 more was coming undone. Pre-load in the pinion bearings was set to 1 Nm and 0,8 Nm in the side bearings, BMW recommend ridiculously high 2,5 Nm in the pinion bearings and about 2 Nm in the side bearings. Backlash was measured in 3 different places on the crown wheel and turned out to 0,05, 0,08 and 0,14 mm, the BMW recommended backlash is 0,05-0,08 but that couldn't be done in my case (rather have a little more backlash rather than less to have sufficient room for lubrication).

Most importantly, don't forget to use Loctite 270 when installing the crown wheel bolts.

This is internet miss information, that is why people say that 4.1 make more noise, that is because they don't properly verify the depth and think is just a swap. but we are all free to do what we want with our cars. information is out there for people to choose what to do.

unless your pinion is marked with the same number, you need to adjust, and even then, you would be a few tenths off unless you have the BMW pinion depth tool and all possible shims to approximate as close to a mathematical nominal.

[Westersund]

Originally Posted by maupineda

This is internet miss information, that is why people say that 4.1 make more noise, that is because they don't properly verify the depth and think is just a swap. but we are all free to do what we want with our cars. information is out there for people to choose what to do.

unless your pinion is marked with the same number, you need to adjust, and even then, you would be a few tenths off unless you have the BMW pinion depth tool and all possible shims to approximate as close to a mathematical nominal.

I did say usually, but you do have to confirm by checking the gear pattern and backlash. You can't just install and assume it will be good to go. No math needed.

I have a step by step guide in my thread over at Rejsa (but it's in Swedish): https://rejsa.nu/forum/viewtopic.php...=asc&start=252

[Vanne]

Sorry for the late reply, yeah agreed, which is exactly why I took mine to a outfit that does just diffs. It's exact work, much more so than I am capable of. I did have a set of 5 different shims to set it correctly, but they came with my race kit from RD. Helpt that the bloke Installing my stuff was Serbian. Lol. There was quite a bit going backwards and forwards to make sure it was all correct.

[grannyknot]

So the diff is all back together, I spent 2-3 days playing with the shims and I got the wipe pattern and the blacklash perfect but as soon as I pushed the stub axles all the way in the backlash seemed to disappear and it took a firmer hand to rotate the pinion from the front.

Stumped I took it up to the diff specialist and they reported the same results that I found, then finally it occurred to us that the only difference between the stub axles in or out was the RacingDiffs HD stub axle seals, those new tight seals were making it feel like there was no backlash.
After a few miles they will settle down and it will feel normal.

Also, after installing the new clutch pack I could not get it to break away no matter how much leverage I used, I took it all apart a few times and couldn't figure it out so as maupineda suggested, I reinstalled my still good original clutch pack and all was good.
Not saying there is anything wrong with RD's clutch pack but I couldn't get it to work.
It might just have needed a few high powered corners wear it in but I didn't want to risk it.

Buttoned it up, installed it in the carrier and got the whole unit up into the car today.