Diff rebuild - available options

[oceansize]

If you had to do it over again (diffsonline order), would you change anything about your order? Different gears or anything like that? Or just keep things the same.

I would do everything the same, really enjoy the 3.91 gears, and one of my favorite modifications.

[ugaexploder]

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.

If you had to do it over again (diffsonline order), would you change anything about your order? Different gears or anything like that? Or just keep things the same.

[Kcalhoun27]

Now we know that with the new clutch stack installed and no more noise, I would think the only noise before should be the heavy M clunk when taking off as the old clutches slipped causing the spiders gears crashed into the side-gears like hammering, but this should not sound like dragging a metal can. What else can cause that dragging can noise?

I legitimately dont know what it could have been, beyond the diff making all that noise. In fairness, i did the diff, both wheel rear wheel bearings, replaced a bunch of the hardware, retorqued everything i could get a wrench on under the car, greased what needed grease, etc.

i can only say that the car is quiet and drives like i suspect its supposed to now. After all that effort, im very happy with how it has turned out. I appreciate all the info from everyone on this forum

[Stilt]

All,

im at the point where my diff sounds like im dragging cans behind my car so its clearly time to refresh

I believe i have 3 options that are reasonable. With the criteria being:
properly working lsd unit that is quiet
new seals/bearings
not buying more than i will really use

so, the options are:
1. diffsonline - m-variable rebuild, nothing fancy. ~$2000 Shipped both ways
2. Racingdiffs parts, still m-variable ~ $800, $5-800 for shop to rebuild, im guessing
3. Wavetrac/Diffsonline seals/bearings - ~$3500 shipped both ways

i would say concern #1 is a properly working diff, that is quiet and i dont have to worry about it. Second is price, meaning that i can pay for any option listed, but dont want to pay more just to prove i can.

can anyone with experience please chime in? Ive read through every diff thread i can find, they are around 3 years old and things change. What was once good may not be any longer and id prefer to do this once and be done with it. Ive put 7k miles on my car the last 5 years so 80k should last my lifetime. If i go the parts route, i trust the shop doing the work, they build 1000hp drift cars for a living and diffs are oil changes for them. I called diffsonline today, and they said they do not sell m-variable parts specifically, so im guessing they save them for their in house rebuild offerings. I emailed racingdiffs and they linked me to their full rebuild kit. So those are the current options available as i see it

i dont track my car, i dont plan to. Its my fun driving car thats pretty to look at. I thought about gearing up a bit, but have decided against that as well, so its just a diff rebuild im looking for now.

thanks for any info

Syncro Design Works, diff rebuild $1400. I'm not sure if they ship, but they are good at what they do.

[sapote]

All,

im at the point where my diff sounds like im dragging cans behind my car so its clearly time to refresh

Now we know that with the new clutch stack installed and no more noise, I would think the only noise before should be the heavy M clunk when taking off as the old clutches slipped causing the spiders gears crashed into the side-gears like hammering, but this should not sound like dragging a metal can. What else can cause that dragging can noise?

[bigjae46]

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

Congratulations!

[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

[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]

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

[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]

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]

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]

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

[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

[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.