Diff rebuild parts advice

[elrichmeister]

So I'm very close to getting my funds for a diff rebuild. Ive been doing to some research in terms how i want to approach this.
I'm like 90% set on changing to 3.85 gears.
So I've been pricing out my 2 paths for this work:

• Purchase the Diff on Diffs Online with 3.85 gear set and it comes out to $2,899 + 1500 core return, so its huge hit initially.
  • https://diffsonline.com/collections/...for-bmw-e46-m3
• Source all parts separately have a local shop rebuild the diff
  • 3.85 Ring and Pinion $1400
    • https://diffsonline.com/collections/...-holes-for-bmw
  • Rebuild Kit - $540
    • https://diffsonline.com/collections/...-differentials

If i source the parts myself, do i need to also get shim kit and clutch pack? Im still looking at other avenues to source parts as well.

[maupineda]

After doing this myself, I would advise for the built unit. The diff rebuild is a very time consuming job to be done right so it needs to be done by a true specialist with access to impossible to get parts that need to be custom made, something diffsonline do for themselves, plus the factory tool to set the depth correctly, which is needed when you regear.

i would still do it myself if I had to do it again as I now have the knowledge, parts and skills to do so. But it ended up being more expensive for me after so much back and forth.

also, don’t do any less than 3.91. 3.85 is just a 6% change and so it will feel like if you remapped the car in chill morning. You will barely be able to tell.

[EthanolTurbo]

Get a 3.91 or 4.1. Go to Pro Gear (who I learned about from EricSMG )in San Diego, parts included they did my diff rebuild and installed the Drexler LSD for $880. If you want them to pull the diff and reinstall it, they quoted an extra $600 for that. I believe they use the DiffsOnline rebuild kit so overall it's way cheaper than any other option.

[Flow]

3.85 doesn't sound like it's worth it imo..
I love my 4.10, event on the freeway there is no issue, and the car is just so responsive with that gearing.


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[elrichmeister]

Ok you guys are convincing me to just get the 3.91. I feel like 4.1 will be too overkill for my use, as I do kind of daily drive the car and use the highway often.

I did speak to Unitrax in Corona CA ( siamkazi referenced them in some other diff rebuild posts recently ) as they a bit more local. They seemed very knowledgeable, I gave them my cars info and they will get back to me on some details.

My main reasoning for this thread was to get some info on the shims and clutch packs as we did discuss those. So I'm just doing some research in case I do need to provide these additional items.

[siamkazi]

I just bought only the shims from Pedro which was recommended. Given some time has passed, I'm very happy with the 3.91 after using it on the freeways and streets.

[maupineda]

I have not tested the racingdiffs stuff long enough, the clutches some say are questionable, other have had success. I literally have only driven like 300miles on them. But I also followed a more conservative approached and stick to OEM like setup so I did not use their shims to preload the unit, also mine is a V2 which is a PITA to do and more unforgiving if you f’up something. Is you car a V1 or 2?

also, if you go to 3.91 you still have the option to play with tire size to achieve the same gearing as a 4.1.

Everything M in UK also seem to have clutch packs, but who knows if he sells them or you must rebuilt with his company.

[elrichmeister]

I just bought only the shims from Pedro which was recommended. Given some time has passed, I'm very happy with the 3.91 after using it on the freeways and streets.

Pedro is from peakyparts right? I sent him a message on Instagram regarding some diff parts, I haven't heard back from him yet. Hopefully I can source what I need from them.

[bigjae46]

$1400 for a 3.85? That's more than a 3.91 or 4.10 brand new. You can get a 3.85 for $400ish used from an E9X M3 6MT.

The racingdiffs clutches have worked fine for me. I did rebuild a couple of the OEM GKN V2s and those have not worked out. Could be me, could be the master tech, could be the clutches...not sure but those would lock up and then quickly turn into a permanent open diff.

If you DIY, you'll need bearings, races, output and pinion seals, carrier o-rings, lock ring, ring gear bolts, and a crush sleeve (get a couple). The kicker is pinion depth...that will eat your lunch. I have gotten lucky and haven't had to make a pinion depth adjustment. But if you can't get the gear pattern centered then you have to press the pinion and races out, change the shim and repeat. I have an extra set of races that are ground down so they are easily installed and removed.

Gearing is gearing. The massive upgrade is in the limited slip unit. A clutch type diff is the way and I think the ZF unit is still the best option.

[siamkazi]

Pedro is from peakyparts right? I sent him a message on Instagram regarding some diff parts, I haven't heard back from him yet. Hopefully I can source what I need from them.

Yeah, that's him. Also, here's his whatsapp, he may respond back if you ping him on here:

[elrichmeister]

So what is consensus on getting new clutch packs? Only one i found was the kit from racing diffs

https://racingdiffs.com/products/bmw-m3-m5-m6-z4m-lsd-differential-rebuild-kit?_pos=1&_sid=c4374bc39&_ss=r&variant=42497704788204

I believe the diff on my car is still on original clutch packs car is approaching 176K miles, should i be ordering new clutch packs to give to the shop, if i have my own unit rebuilt?

[jayjaya29]

So what is consensus on getting new clutch packs? Only one i found was the kit from racing diffs

https://racingdiffs.com/products/bmw-m3-m5-m6-z4m-lsd-differential-rebuild-kit?_pos=1&_sid=c4374bc39&_ss=r&variant=42497704788204

I believe the diff on my car is still on original clutch packs car is approaching 176K miles, should i be ordering new clutch packs to give to the shop, if i have my own unit rebuilt?

Nearly everything racing diffs makes is a waste of your money, especially the friction discs.

[maupineda]

Nearly everything racing diffs makes is a waste of your money, especially the friction discs.

Not 100% true, the bearings are genuine Koyo, which are the factory option. Also the steel plates can be sourced separately, and the shims is up to you if you do them. The way I see it is that as long as you rebuild to the OE setup their clutches are fine. Their latest kit have you preload the hell out of the unit and that for sure will wear those quicker. There are a lot of bad misconceptions about rebuilding the viscous GKN units.

the M clunk fix is pretty easy with 2 * 0.1 shims on the bottom side gear. I documented all this in my build thread.

[jayjaya29]

Their clutches simply do not last as long as OE-equivalent units. They are attractive due to their price but you get what you pay for. The bearings and items they do not make but supply are fine.

[elrichmeister]

Well i think im going to go through Peaky Parts for 3.91 RP, Shims, Bearings for rebuild parts, and having a DIff shop rebuild the DIff with Wavetrac LSD.