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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Thu, Aug-16-2018, 09:52:51 PM   #1
sddynamix
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Default Digging into the Diff Rebuild

I know there are a few posts about diff rebuilds here, so I'll try to be as specific as I can.

My car recently rolled over 200k miles, and I noticed there was a bit of howling coming from the rear end at highway speeds. Tires have been replaced (incidentally, due to nail + tire age) with PS4S's, and that didn't make a difference (5000 miles ago). I also replaced the wheel bearings with new OEM units. Subframe was reinforced last year. Man, axles suck to remove and reinstall.

So I figure it's time to replace the bearings and seals on the diff itself. But the shop I am going to use charges the same labor rate to drop the diff and do the work, so I'm curious if at this mileage/age (2003, and 200k miles), it's worth rebuilding or replacing the M-Variable LSD itself. The shop said that I can supply this part because they have no direct line to obtain it themselves.

I've read a few posts about this not being user-serviceable, but I see places like diffsonline selling fully rebuilt units, with rebuilt M-Variable LSD's. I didn't see the LSD's themselves for sale on their website though.

So my questions:

1 - Should I bother replacing this while they're in there, or are there symptoms/signs I should be looking at? I also see a lot of posts about our LSD's being pretty bullet proof. But if I'm paying the same labor rate, I want to refresh as much as I can.

2 - Where would I buy just the M-Variable LSD?

Thanks!
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Old Thu, Aug-16-2018, 10:11:13 PM   #2
TboneM3
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Default Re: Digging into the Diff Rebuild

Well your LSD is toast at this point, so if you would like a working LSD (which is a huge deal btw), you should get a whole new diff from diffsonline or have yours rebuilt, but def with a new or reman'd M-LSD. There are other types of LSDs out there though, so do your research. I'd also shop around more on the shop that rebuilds it. Look at off road truck shops. A diff is a diff.

Not sure what you saw about our LSDs being bullet proof. They have a life of around 100k like a lot of things on this car. the Diff itself, like the tranny, is pretty bomb proof, however, and 75w140 is a nice heavy oil (upgraded from 90weight from e36)
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Old Thu, Aug-16-2018, 10:16:35 PM   #3
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Default Re: Digging into the Diff Rebuild

IMO. If you use the car for daily driving and no track use, just get it rebuilt or look for a used unit to swap. If you do track the car or just want to spend the extra cash definitely upgrade the M-Variable LSD, because quite frankly it sucks.

Contact Jim at Performance Gearing. Great guy, super knowledgeable, and is very passionate about what he does. Had him rebuild a number of units with nothing but great things to say.
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Old Thu, Aug-16-2018, 10:22:19 PM   #4
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Default Re: Digging into the Diff Rebuild

Quote:
Originally Posted by TboneM3 View Post
Well your LSD is toast at this point, so if you would like a working LSD (which is a huge deal btw), you should get a whole new diff from diffsonline or have yours rebuilt, but def with a new or reman'd M-LSD. There are other types of LSDs out there though, so do your research. I'd also shop around more on the shop that rebuilds it. Look at off road truck shops. A diff is a diff.

Not sure what you saw about our LSDs being bullet proof. They have a life of around 100k like a lot of things on this car. the Diff itself, like the tranny, is pretty bomb proof, however, and 75w140 is a nice heavy oil (upgraded from 90weight from e36)
Thanks for the response! The car is a DD, so I don't think I'll reap any benefits from upgrading the M-Variable to something else. The shop in question is specifically a shop in San Diego that works on diffs and axles (that comes highly recommended from other forum members locally). They do everything, except rebuild the LSD unit itself, because they don't have a direct source for parts.

I think the issue with the "LSD is bullet proof" statement is that too many folks are using LSD to describe the entire diff, so it's a point of confusion.

Quote:
Originally Posted by cosmos///m3 View Post
IMO. If you use the car for daily driving and no track use, just get it rebuilt or look for a used unit to swap. If you do track the car or just want to spend the extra cash definitely upgrade the M-Variable LSD, because quite frankly it sucks.

Contact Jim at Performance Gearing. Great guy, super knowledgeable, and is very passionate about what he does. Had him rebuild a number of units with nothing but great things to say.
Yes, that's exactly what I'm looking to do - getting the entire diff rebuilt (with new bearings, seals), as well as a rebuilt or replacement M-Variable LSD.

So the remaining question then is - where can I get a hold of just the new or reman'd M-Variable LSD?
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Old Thu, Aug-16-2018, 10:24:38 PM   #5
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Default Re: Digging into the Diff Rebuild

There is actually someone in europe that makes clutch pack replacement for the M Variable GKN diff. https://www.racingdiffs.com/bmw-lsd-clutch-plates/
If you were rebuilding then I would get new seals along with input and output bearings while you are in there.
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Old Fri, Aug-17-2018, 03:05:47 AM   #6
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Default Re: Digging into the Diff Rebuild

Subd. Been looking into rebuilding my diff.
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Old Fri, Aug-17-2018, 04:50:54 PM   #7
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Default Re: Digging into the Diff Rebuild

Now is a great time to get away from that 'M-Variable Clunking' diff!
Also recommend contacting Jim Blanton. His diffs aren't cheap, but he knows of what he speaks.
Heard good things about OS Giken (and Wavetrac too, but not so sure of its locking ability). If it's a daily, a Quaife might be perfect...
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Old Fri, Aug-17-2018, 05:02:45 PM   #8
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Default Re: Digging into the Diff Rebuild

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Originally Posted by tofunin View Post
There is actually someone in europe that makes clutch pack replacement for the M Variable GKN diff. https://www.racingdiffs.com/bmw-lsd-clutch-plates/
If you were rebuilding then I would get new seals along with input and output bearings while you are in there.

Thank you for posting this info.
With replacement friction plates available, might be worth rebuilding.
Shim up all that excess backlash in the spider gears, and it'll stop clunking too.
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Old Fri, Aug-17-2018, 08:44:27 PM   #9
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Default Re: Digging into the Diff Rebuild

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Originally Posted by nowanker View Post

Thank you for posting this info.
With replacement friction plates available, might be worth rebuilding.
Shim up all that excess backlash in the spider gears, and it'll stop clunking too.
Interested in this as well. I've been searching for a decent DIY but haven't found one.
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Old Mon, Aug-20-2018, 05:15:38 PM   #10
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Default Re: Digging into the Diff Rebuild

Thanks everyone - anyone actually rebuild their LSD with the parts from racingdiffs?

Also still looking for a lead on an already-rebuilt LSD unit.

EDIT: Looks like Racing Diffs have these too, I've sent them a message. Any other leads would be much appreciated!
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Discussing Digging into the Diff Rebuild in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)