Differential Shims

[sapote]

I had a pretty serious "M clunk" from my diff before the rebuild and it's completely gone now. I replaced everything in the diff with exception of the LSD carrier and spider gears, and obviously set backlash and preloads within tolerance. I'll never know if the clunk would have been resolved with the fresh OEM parts alone or if the "free play fix shim" did it. There's still a noticeable amount of free play in the right axle and no clunk, so I think the clunk would have been eliminated with the rebuild alone. Diff bushings were also replaced which may have helped too, but the originals didn't look bad and probably didn't contribute to the clunk in the fist place.

Luckily my diff needed thinner shims for proper preload, so I cheated and planed the original shims down little by little until they were perfect. I don't know if that's advisable, but seems to have worked so far.

I don't have any feedback on the LSD clutch plates yet. I'm still in the break-in period for the new gears and haven't driven her hard yet.

I doubt if the new clutch set and the "free play fix" shim solved the major clunk.
1. The clutch disks have nothing to do with the clunk.
2. The "free play" spring washer takes out the gear lash in the spider gears, but since it is thinner than the stock shim, its concave shape will be flatted down under acceleration load, and this will move the diff RHS output flange outward. This axial outward motion under load, and inward motion when coasting, will lead to the RHS oil seal leaking sooner than stock setup. If I want to reduce the spider gears backlash, I would rather use a thicker spider gear shim on the RHS than using a spring washer. Also, during turning the corner, the concave washer will spin against the carrier thrust surface, leading to a faster wear on both surfaces as the thrust bearing surface now is just a thin circular line instead of the whole shim surface of the stock shim. So this "free play fix" will not last that long in an oval track or road.

3. "Luckily my diff needed thinner shims for proper preload"
I think these are the output flange shims for preloading the taper roller bearings, as the old bearings slightly worn down. This determines the pinion/ring gear backlash, and could affect the diff noise.

As about what fixed the major clunk, I think torqueing the 3 diff bushing bolts probably to spec had done it. The front bushing bolt is under a lot of force during heavy acceleration, and so sooner or later the diff will push the bolt/washers upward against the bushing center core during forward acc, then it will push the bolt downward against the bushing core during engine braking. The cycle repeated and very soon the washers and the core thrust surface worn down, then it clunks.

Why the RHS output flange has more plays than the LHS? Because RHS spline shaft is shorter and has less support radially. The left shaft is longer because it also drives the clutch set, and so it has more support radially. Of course the less backlash in the spider gears, the more rigid the output flanges. I don't know why all spider gears -- different model cars -- tent to have much more backlash than other gears, i.e. transmission gears. Maybe due to their small diameter and low tooth count, they need more backlash to run quiet. I also don't think the backlash in spider gears causing the M-clunk.

[sapote]

It appears BMW no longer sells diff shims for our car. I found Racing Diffs sells shims but shipping is around 21 days from Serbia (their location) to the USA.

Does anyone have other sources for diff shims? I checked ebay but I couldn’t find any sourced from the USA.

Which shims? All the shims used in the diff (pinion gear depth shims, output flange roller bearing shims, spider gears shims).

[0-60motorsports]

Its very annoying that they do not sell the Free play delete (fix) shim on its own anymore

[sapote]

Its very annoying that they do not sell the Free play delete (fix) shim on its own anymore

Just use the normal shims. I'm sure one can source these shims at MacMaster and get them in different thickness. The OD and ID are not dimensionally critical as long as it fits over the side gear shaft and sits flat on the carrier thrust bearing surface.

[Arith2]

Can we get a standard shim measurement? I'd rather not be stuck without a car for weeks waiting on custom shim. Charging $200-$500 is unethical. Let's not get ripped off and figure this out. It defeats the purpose of doing a rebuild. Doing it ourselves should balance out but these companies are making it so expensive, it's better to use them. This should not be the case. The fact that diffsonline sells the shim kit for $500 turns me off to their whole business. Other shim SETS are literally $15. Let's use capitalism to our advantage and drive down the prices.

[sapote]

We just need the dimension of 2 shims: the RH side gear (which drives the RH output flange), and the output cover shim (this is the big on to shim the carrier left and right roller bearing). Just get them in different thickness from MacMaster.

[Tones]

Can we get a standard shim measurement? I'd rather not be stuck without a car for weeks waiting on custom shim. Charging $200-$500 is unethical. Let's not get ripped off and figure this out. It defeats the purpose of doing a rebuild. Doing it ourselves should balance out but these companies are making it so expensive, it's better to use them. This should not be the case. The fact that diffsonline sells the shim kit for $500 turns me off to their whole business. Other shim SETS are literally $15. Let's use capitalism to our advantage and drive down the prices.

Supposedly diffs online makes their own parts. I talked to other diff part manufactures and they find that kinda hard to believe but don't actually know.



I do know that diffs online upped their core charge from 700-1200.

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[oceansize]

Supposedly diffs online makes their own parts. I talked to other diff part manufactures and they find that kinda hard to believe but don't actually know.
I do know that diffs online upped their core charge from 700-1200.

Dang. My core charge last year was 750 and you can bet I had that thing boxed up and sent back in a hurry. I also noted their 3.91 diff price has gone up $200 since I ordered mine last May. I will say the new 3.91 diff has been perfect.

[Tones]

Dang. My core charge last year was 750 and you can bet I had that thing boxed up and sent back in a hurry. I also noted their 3.91 diff price has gone up $200 since I ordered mine last May. I will say the new 3.91 diff has been perfect.

Yeah I need a diff rebuild. Got that clunk going on when you move the wheels in the air.

I bought racing diffs rebuild cuz it was cheap like 200 but I'm out here in rural Hawaii and trying to find a machine shop that wants to deal with it is not easy. And I don't trust em lol.

How much was your shipping? They quoted me like 300 one way to Hawaii so that would put the whole cost to like 1900 for a stock rebuild.

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[oceansize]

Yeah I need a diff rebuild. Got that clunk going on when you move the wheels in the air.

I bought racing diffs rebuild cuz it was cheap like 200 but I'm out here in rural Hawaii and trying to find a machine shop that wants to deal with it is not easy. And I don't trust em lol.

How much was your shipping? They quoted me like 300 one way to Hawaii so that would put the whole cost to like 1900 for a stock rebuild.

$99 dollars one way to TN, so 300 seems about right as he is on the NE coast of the continental US.

[Mspir3d]

Yeah I need a diff rebuild. Got that clunk going on when you move the wheels in the air.

I bought racing diffs rebuild cuz it was cheap like 200 but I'm out here in rural Hawaii and trying to find a machine shop that wants to deal with it is not easy. And I don't trust em lol.

How much was your shipping? They quoted me like 300 one way to Hawaii so that would put the whole cost to like 1900 for a stock rebuild.

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If you aren't planning on replacing the bearings or changing gear sets, it's a pretty simple and straight forward job. You do need a 6 inch bench vise as some of those bolts are stupid tight. I rebuilt mine over the winter and it's been doing well considering the 700 ft lbs I'm putting through it. I left the free play shim out though being overly cautious.

[Tones]

If you aren't planning on replacing the bearings or changing gear sets, it's a pretty simple and straight forward job. You do need a 6 inch bench vise as some of those bolts are stupid tight. I rebuilt mine over the winter and it's been doing well considering the 700 ft lbs I'm putting through it. I left the free play shim out though being overly cautious.

Did you need a press? I watched the Video on racing diffs and it didn't look that bad. I'm just in the middle of finding a new house. Once I got that I'll tackle this

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[sapote]

“You do need a 6 inch bench vise as some of those bolts are stupid tight.”
What if you loosen the ring bolts while the carrier is still in the diff housing? Put it in 1st gear, lock up hand brake, loosen them via the removed cover?

[Mspir3d]

Did you need a press? I watched the Video on racing diffs and it didn't look that bad. I'm just in the middle of finding a new house. Once I got that I'll tackle this

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To replace the bearings you will need a press. If you are only replacing the clutches, it’s not necessary.

Looking at a picture I have of the differential, I don’t think there is enough room to get a socket on the bolts with the lsd in the car. Some of the bolts came loose with a borrowed Milwaukee impact wrench. There were several on mine that took a big breaker bar with a jack handle on the end to break loose. I wedged the plastic end of a screw driver through a hole for the axles to keep it from turning in the vise.