E46 M3 Differential Input Shaft Seal Guide + M-Clunk Diagnosis, Refitting the Diff & Test Drive

E46 M3 Differential Input Shaft Seal Guide + M-Clunk Diagnosis, Refitting the Diff & Test Drive

Following on from the previous video where I removed my BMW E46 M3 differential and brought you up to speed on the car and its multiple diff problems, this time I compare two diffs on the bench, swap the input seal, refit, and find out if the “known good” second diff I picked up was a scam or not.

Here's what I used in this video:
Uprated Input Shaft Seal: https://ebay.us/acTmK6
BMW Revised Diff Bolts: https://ebay.us/c2tVLr
Castrol Transmax Limited Slip 75W140 Oil: https://ebay.us/Vqaciq
Original BMW SAF-XJ 0.5L + FM Booster 83222282583: https://ebay.us/rzk23W
Jenolite Wax Oil Spray: https://ebay.us/fDAS70
E-Torx Spanners: https://ebay.us/LAkQFk
E-Torx Sockets: https://ebay.us/YPEsBZ
Dewalt 18v 3/8 Ratchet: https://ebay.us/Wk14qg

With my original E46 M3 diff on the bench beside a spare one I picked up described as "known good" I was finally able to compare them and determine if there are any obvious issues with the original or at least points of difference in terms of play.

Surprisingly the new diff I picked up seemed to be clanking more when I span the input flange by hand, but I was correct in suspecting this was more to do with the fact it was drained of oil than anything.

The most prolific cause of E46 M-Clunk is said to be the right-hand output flange of these M3 differentials. Due to the design of the internals, the right-side flange has a shorter spline into the diff, and develops play over time, leading to clunks.

The new differential I had seems to have significantly less play versus the original one, which was encouraging to me. Further to that, my original diff seems to behave strangely to inputs, if you let the diff settle for a moment, it's very stiff to start it turning, almost feels like it seizes up slightly. When its turning however, it turns freely, it's just getting it to start.

With that strange development, I concluded fitting the new differential was the best move, so this is the unit I opted to fit my new input shaft seal to.

The new input shaft seal I picked up is an uprated part which is supposedly improved from BMWs original seal, it uses a cup design rather than a grooved design to prevent the diff oil from escaping. I believe its the grooves on BMW's design which wear down over time and permit the leaking of oil.

The video serves as a good guide for replacing the pinion seal on your M3 diff. First remove the input flange by careful removing the nut which holds it in place. Count the threads as I did, as its absolutely essential that this nut is put back in exactly the same position as it was originally. It doesn't just hold on the input flange, it also sets the thrust of the pinion on the crown wheel. Setting it incorrectly will terminate your differential prematurely, and it will probably make a horrific noise while in demise.

with the input flange nut, and the flange itself removed, extract the original diff seal and get your new one carefully pressed in. Button it back up and your job should be done, no more diff leaks.

After doing this successfully, fitted the diff to the car using new rear bolts, the revised E-torx ones with the shoulder supplied by BMW. It was quite tough but with help from he old man and a bit of bickering, we managed to get the diff in place, the torque settings are shared in the video too.

I'd fitted the spare diff with the original diff's oil, the stuff supplied by BMW I'd put in only a few thousand miles previous, and topped up with some Castrol limited slip oil to meet capacity.

Following a 50 mile test drive, which included some tight circles to circulate the diff oil into the clutch packs and reduce the groaning noise, and some spirited driving, I concluded that my M-Clunk is considerably improved. Although still present, it's considerably reduced.

For more helpful how-to guides and restoration project logs, visit our blog: https://www.spannerrash.com/

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