Diff rebuild - available options

[oceansize]

Diffsonline, like everything else, has gone up a bunch. My 3.91 in 2020 was 2500 (not including core charge) and is now 3200. This is one of those items I didn't want to fool with and didn't want to do twice (or more). Been very happy with Dan's work.

[sapote]

[QUOTE=Kcalhoun27;n261961]Noisy when shifting and a bit when turning. Im also doing the wheel bearings because ill have the rear end torn apart, but from all the reading ive done, im confident the diff is the main culprit for the noise

/QUOTE]
Seeing the front mounting bolt is necked, this caused great noise.

Would just replace the output seals, o-rings, new clutch stack, reduce the side gears plays with flat shims.
But measure the total thickness of new clutch stack excluding any spring plates, and compare with the old stack first before installing

[Kcalhoun27]

[QUOTE=sapote;n262363]

Noisy when shifting and a bit when turning. Im also doing the wheel bearings because ill have the rear end torn apart, but from all the reading ive done, im confident the diff is the main culprit for the noise

/QUOTE]
Seeing the front mounting bolt is necked, this caused great noise.

Would just replace the output seals, o-rings, new clutch stack, reduce the side gears plays with flat shims.
But measure the total thickness of new clutch stack excluding any spring plates, and compare with the old stack first before installing

The stretched bolt is from the rear cover, its definitely not right, but it wasnt the cause of the noise. Im just glad it didnt break off in the housing, that would have been an absolute nightmare

i know that Gizmo said there should be some free play in the right output shaft but id be surprised if the amount i have is considered acceptable. It certainly isnt to me, and based on what info i have found, at least the racingdiffs parts aim to fix that issue. Im not a mechanical engineer, so i dont know exactly what they were thinking but after 24 years in aviation thats a lot of forward/aft movement for a rotating part and i suspect it cant be helping

that said, i dont think ill have a good answer until the new parts are installed.

i checked the other hardware, the front diff bolt looks healthy and the rear bolts are the new versions, replaced 3 years ago with ~1000 miles on them, although i will be replacing the hardware just in case

[sapote]

know that Gizmo said there should be some free play in the right output shaft but id be surprised if the amount i have is considered acceptable. It certainly isnt to me, and based on what info i have found, at least the racingdiffs parts aim to fix that issue. Im not a mechanical engineer, so i dont know exactly what they were thinking but after 24 years in aviation thats a lot of forward/aft movement for a rotating part and i suspect it cant be helping

All Diff output flanges have that much plays, including open Diff. So don’t be surprised.

As advised, RacingDiff concave shim is not a good solution as it causes other things to wear faster. If you want less plays then add flat shims.

[Cubieman]

Another vote here for diffsonline standard M-varible, the 4.10 diff my vehicle came with was one of theirs, it's been in there for about 30k without issue.

I also had my M6 diff (similar to M3) sent to diffsonline for a standard rebuild 5 months ago and it's doing just fine, granted not many miles on it, but it is quite as can be and has less driveline slack.

[Kcalhoun27]

Well, for anyone that cares, i decided to take a two-step approach
i ordered the racingdiffs parts and will be taking on the task of the refresh myself because it sounds like a good challenge. If i get stuck, i can go to the shop here that is more than capable and if i totally screw it up, i can always cry uncle and send it to diffsonline to have the experts do their magic.
i think i always wanted to try that route and just didnt believe i could. So i guess im going to learn my limits on this
thanks for any advice given

[Kcalhoun27]

Well, rebuild went well, as far as i can tell. Took my time cleaning parts, making sure new parts were well oiled as they went in, loctite applied as necessary, etc.
i still have more work to do before i can go for a drive, but im hoping to be back on the ground and put together by next week.

i did have some trouble with the inner gear teeth aligning and had to disassemble and reassemble the unit in order to better line up the teeth. Lesson learned there. Thought i had done that but actually it needed to go in a bit further in order to confirm the teeth were aligned for assembly. Easy thing to overlook i suppose, annoying that i didnt overlook it, but still got it wrong.

all in all, i think anyone with some mechanic skill could do the work ive done, assuming the car drives and doesnt make a ton of noise like before, id put it below the vanos fix in terms of difficulty

[bigjae46]

Well, rebuild went well, as far as i can tell. Took my time cleaning parts, making sure new parts were well oiled as they went in, loctite applied as necessary, etc.
i still have more work to do before i can go for a drive, but im hoping to be back on the ground and put together by next week.

i did have some trouble with the inner gear teeth aligning and had to disassemble and reassemble the unit in order to better line up the teeth. Lesson learned there. Thought i had done that but actually it needed to go in a bit further in order to confirm the teeth were aligned for assembly. Easy thing to overlook i suppose, annoying that i didnt overlook it, but still got it wrong.

all in all, i think anyone with some mechanic skill could do the work ive done, assuming the car drives and doesnt make a ton of noise like before, id put it below the vanos fix in terms of difficulty

It's not rocket science by any means. BMW makes it much easier. The barrier for most is access to tools and its a somewhat physical job...everything is heavy.

[Kcalhoun27]

It's not rocket science by any means. BMW makes it much easier. The barrier for most is access to tools and its a somewhat physical job...everything is heavy.

Youre not lying about the weight. Getting that diff back in the car was a chore on my own.

i guess my point is that its not as hard to do as many on this forum have implied. Reading and watching videos did a lot for me. Having a neighbor thats a shop tech for the state helped a lot as well. I hope that a) my work is successful and b) based on that, more people can feel confident that the job is doable. You, among others, were good sources of info and i appreciate it

[bigjae46]

Youre not lying about the weight. Getting that diff back in the car was a chore on my own.

i guess my point is that its not as hard to do as many on this forum have implied. Reading and watching videos did a lot for me. Having a neighbor thats a shop tech for the state helped a lot as well. I hope that a) my work is successful and b) based on that, more people can feel confident that the job is doable. You, among others, were good sources of info and i appreciate it

Glad I could provide some useful info...which I got from others as well.

100% agreed. Preload and backlash are objective measures. There is an art to reading a gear pattern but if the backlash is good then the gear pattern should also be good. Don't over complicate it.

I remember building my first diff I overcrushed 3 sleeves. I was on the last one (I was prepared!) and thankfully I got it spot on.

[Kcalhoun27]

Well, i dont want to jump the gun, but initial drive was a success! All the clunking noises are completely gone and just for the sake of knowing, i laid down two nice skids to make sure both tires were driving.

i need to leak check, do a bit of inspecting, and double check the diff fluid level, but im hopeful for a job well done

[sapote]

Well, rebuild went well, as far as i can tell. Took my time cleaning parts, making sure new parts were well oiled as they went in, loctite applied as necessary, etc.
i still have more work to do before i can go for a drive, but im hoping to be back on the ground and put together by next week.

i did have some trouble with the inner gear teeth aligning and had to disassemble and reassemble the unit in order to better line up the teeth. Lesson learned there. Thought i had done that but actually it needed to go in a bit further in order to confirm the teeth were aligned for assembly. Easy thing to overlook i suppose, annoying that i didnt overlook it, but still got it wrong.

all in all, i think anyone with some mechanic skill could do the work ive done, assuming the car drives and doesnt make a ton of noise like before, id put it below the vanos fix in terms of difficulty

Inner gear teeth -- you mean the pump and the clutch stack splines are not aligned (and the side-gear not aligned if their concave shim is used) to insert the output flange in ?

How many clutch plates in the kit and does it also have the big spring shim/washer under the pump?

[Kcalhoun27]

Inner gear teeth -- you mean the pump and the clutch stack splines are not aligned (and the side-gear not aligned if their concave shim is used) to insert the output flange in ?

How many clutch plates in the kit and does it also have the big spring shim/washer under the pump?

Yes, they were slighty turned, so i had to un-do my work and make sure i took a second look when i put everything back together again. It might seem like an obvious thing, but the teeth can turn ever so slightly and then the splines will not easily feed into them.

easy enough to fix, i doubt id make that mistake again

as for the clutch stack, i believe it was 6 spacers and 5 friction plates. There were 2 separate spring shims, one under the lower spider gear and one at the very top of the stack. Its tough to know exactly how much pressure they impart, as the fitment is tight to begin with