So, on with the diff assembly!
First off the E36 pinion into the E21 case with new bearings.
Place the pinion in the freezer
And this bit in the oven
And then simply drop the bearing onto the pinion! (no, seriously, it just dropped straight on)
Next the outer races into the case. You'll notice I stuck these in the freezer as well, but it didn't really make that much difference to be honest.
While we're at it, this is the difference between the E21 3.63 pinion and bearing and the E36 3.38 pinion. you can clearly see the size difference in the bearings and the slightly longer teeth of the 13 tooth (3.38) pinion.
Then assemble the pinion WITHOUT the crush sleeve or seal - just tighten the nut until you reach a specific torque to turn. In my case this was 2.5kg @ 10cm from the centre (or 2.5nm if you happen to have a torque gauge). At this point you need to measure the pinion depth and adjust if necessary. BMW specify this from the face of the pinion gear to the centre of the carrier bearing holes, which required some awkward measuring and some maths. You adjust this by changing the shim that sits behind the inner pinion bearing race in the case. I had 3 shims to choose from and some 0.1mm shim washers just in case, typically it was the 3rd one i tried that got me closest to the specified depth.
With that done, you need to set the carrier bearing pre-load and then the ring gear back lash. Ideally, you'd have a selection of shims available for the carrier bearings to do this, but at about £15 a pop i decided to make some out of some 0.5 and 0.1mm shim washers.
The carrier pre-load is set by the total shim thickness, and you need to determine this first. Again, it's a torque to turn value of around 2.5nm. Once you have the total shim thickness you halve this as a starting point for the backlash adjustment. The backlash is set by the thickness of the left hand shim, with the remaining shim thickness added to the right hand side to make up the pre-load. Backlash spec was between 0.05 and 0.15mm and needs to be measured in several places around the ring gear to obtain an average
Once that is set you can check the contact pattern. Now, you can buy marking paste for this, but a bit of Cadmium yellow oil paint seems to do the trick. Simply paint a few ring gear teeth and rotate the pinion while applying pressure to the ring gear both forwards and backwards.
At this point you may need to adjust the backlash and/or pinion depth depending on what the contact pattern looks like, Mine was looking pretty good much to my surprise! To be honest, if you've got the pinion depth set correctly and the backlash set correctly it should be pretty damn close - I expect this is how they are assembled in the factory.
With all that done you then get to take the whole thing apart again so you can install the pinion crush tube and the pinion seal. Then torque the pinion nut properly, this time to 3kg @ 10cm (3mn) to account for the added drag of the seal. It takes some serious force to crush the crush tube, I had the pinion holding tool in a vice and a 6 foot scaffold pole on a breaker bar to get it done.
Then i could finally assemble the limited slip carrier with the new clutch plates etc
As it's an E36 centre it won't actually fit in the E21 case with a ring gear on it - you need to stack all the plates and springs in the carrier, then slide it into the case, then slide the top cap in and torque the bolts down awkwardly like this
With all that done, it's really just a case of bolting the rest back together. The carrier bearing plates got new o-rings and new output shaft seals, and new bolts were used everywhere. I used silicone in place of a gasket to seal the rear cover.
You'll also notice i added a trigger wheel to one of the output flanges, this was one of the ones removed from the E36 diffs, and it was a perfect fit around the E21 dust shield.
Combine this with a speed sensor and a fabricated bracket and my speedo should work finally!