The WTF differential e36

[Pyropete82]

Ok so,
M3 1995 and before was 6 bolt input shaft to differential
M3 post 1995, all 4 bolt, minus the fact that 1995 had weird things going on (4 and 6 bolt available on m3)

First, do I have these assumptions right?

Second, see the photos I have below of a 1997 M3 manual sedan LSD, 6-bolt...owner says it's stock, he wasn't first owner...did BMW do something "special" for the m3 manual sedan?

Btw, I'm trying to figure out if there is a cost effective way to swap to the 4 bolt setup without pulling the input shaft and without using a different drive shaft.

This would be going into 1996 vert 328I, I haven't seen if I have 6 bolt, but I'm sure I have 4?

[BimmerBreaker]

Just for posterity's sake ... look at what your car has now first...

There was certainly some inconsistencies with diffs in the late '90s BMWs.

[pbonsalb]

Apparently some obd2 era E36 have 6 bolt input diffs. Don't know any definitive cutoff. Input can be changed to 4 bolt.

[Pyropete82]

Do we know definitively that the thickness of the input shaft sleeve of a 6 vs 4 is the same, meaning will the shaft nut thread down to the same location it was at before removal to ensure preload? Swap nuts with the swap?

[Pyropete82]

We definitely know I'm on a 4 bolt flange I just checked today, and this dif is definitely a 6 bolt, so back to my original question, I know I can swap the 4 with the 6 but no one can commit that the flange lengths are the same. I know I have certain torque that the Bentley manual calls for but I'm concerned about the preload without knowing for certain the flange lengths match. So, I know I'm going to check the preload with a torque dial...I guess as long as I have torque and preload I'm set. I have one shot at this! It's my DD so it better work

[pbonsalb]

If you screw up the preload you can damage the diff. However, many have swapped 4 bolt input flanges for 6 bolt and vice versa after carefully marking the nut and shaft to get the exact same torque. For a couple of years, I ran a 3.15 6 bolt diff that was swapped to a 4 bolt. No issues. But you have to do it carefully. If you search in the M3 and E36 forums, you will find some information on this. The information is controversial. Some say you will ruin the diff and must diassemble it and change the crush bearing, which is a much more involved job although the crush bearing is cheap. Others say that is not necessary. Mine was done by one of the best diff shops around, diffsonline.com and he did not change the crush bearing so take what you read from internet experts, myself included, with a grain of salt.

[Pyropete82]

Yeah I just shot the dealer a message here in CA hoping I drop both diffs off, offload 1 to them and get the flanges swapped

[Butters Stoch]

I've seen people just "drill" the flange and add bolt and nut. 2 will already line up. These were people scared of swapping flanges.

[Pyropete82]

Found a guy on eBay with a 4 bolt flange. $30, just bought it. I think I'm going to invest in a dial torque wrench and the backlash dial also just to make sure I'm good on both front and back ends after I swap them. I do not plan to replace the crush sleeve. I figure I got the diff for $180, so it's worth the tlc at this point. I'm seriously contemplating cracking the diff open and replacing the 2 clutches inside. If I do this myself and correctly of course it will save me approximately $600 when compared to the $1300 plus ship from diffsonline

[Pyropete82]

Ugh, cracked the differential open only to be disappointed....looks like 2 bolts sheared from last owner. How do I get these bolts out without damaging the threads?

SOB! Just cleaned one edge, sheared another bolt and found a crack....this bearing housing is done for...now how do I find another? Will my 2.93 open on my convertible work? Or this officially a done deal?

[Pyropete82]

****Update****
Got those damn screws out! Success. Now can I swap the diff cover?
Took 2 hours to remove 3 screws, broke an ez out inside...

[Pyropete82]

So I brought it to the machine shop and the guy said he can't weld it because he will warp it. I think the guy is pulling my chain and just didn't want the small job. So I'm going to try my mechanic next and see what they say.
If the warping thing is true, then I might just risk it and reinstall it. There aren't a whole lot of forces acting on this area, bolts are there to hold the diff straight, so 1 bolt shouldn't make too much of a difference.

[Pyropete82]

Haha, just ungreased the pinion nut, not sure why it had bearing geese all over it, but it looks like someone removed this before. There is writing on the pinion shaft +5 is what it says, with marks. So it looks like someone swapped this diff at some point for some reason. Now I'm thrown through loop here. This came from a 1997 m3 manual sedan, which by default is supposed to be a 4 bolt flange; this was 6. I'm starting to think the donor here came from a 1995 m3...which means this is not a 3.23 and the PO got into a bad rear end forcing a diff and shaft swap?

I guess I will count pinion gears and ring gears for ratio....:ultra confused:.

[Pyropete82]

Counted and confirmed 42:13, 3.23 indeed. Bentley manual calls out the drive flange to axle m8 be torqued to 22 ft lb. Lash looks good. Going to break the input flange nut soon and replace with the 4 bolt input flange. The rebuild is turning out ok thus far, first time doing it and honestly it's pretty easy.

So, the WTF Differential is solved! This did come from an s52 manual, and is a 3.23 with 6 bolt pattern. Conclusion, BMW couldn't get the bolt pattern right for the e36.

[pbonsalb]

There could be a couple of explanations -- bad DS so someone swapped in a 6 bolt and had to change the diff input to match. Or BMW was using up some old DS and diff parts (they would have had to have spare 6 bolt DS with rear CV joint to go with the spare 6 bolt input shaft since later DS have a rear u-joint instead of a CV). All these old diffs should be inspected and at a minimum have those bolts replaced before they back out and break something or cause the cover to crack. Your DIY experience will hopefully lead others to do this, although you ended up doing a more thorough job.