Hilton

Well ok, not exactly questioning.. but in the workshop manual, it says the drive pinion mustn't be installed when shimming the diff for bearing preload (working out S-tot to use the WSM terminology).

I'd like to avoid putting the diff carrier bearings on without the crown ring / wheel, measuring the total shim depth needed for S1 and S2 shims on the two side-plates, and then removing the bearing to add the speed sensor and crown wheels, to put it all back in and set backlash. It just seems like unnecessary risk of damaging the bearing to pull it again, plus I'm lazy (and have a scary wobbly two-jaw puller).

So my question is..

If I assemble the diff carrier with both bearings, crown wheel, speed sensor wheel, can I still measure the total shim gap by doing it on the opposite side to the workshop manual's stated ring gear end, and having both the crown wheel and pinion in?

The workshop manual (see attached image below) presumably doesn't want the pinion there as the crown will possibly interfere with the pinion when you clamp down the ring gear side plate. This interference would give too small a shim measurement at the gap on the other side plate, as the diff carrier would be binding against the pinion.

However, as far as I/we can see, clamping the non-ring gear side plate down would move the crown wheel away from the pinion so that the possible total gap wouldn't be impacted by the drive pinion still being in there.

If you're wondering why I'm even doing this.. its to add a limited slip differential to my '89 manual S4. (so pinion/crown aren't changing.. just have to move the crown to the "new" diff.

Oh - one interesting data-point. Greg Brown mentioned in a thread elsewhere that when installing a used pinion and crown wheel, 20% should be added to the specified backlash for that gear set to account for wear. I measured mine before taking it apart and got 0.1625mm backlash (averaged over 4 compass point readings), versus spec of 0.14mm. So 16% more than specified. Or, put another way, there was 0.02mm of wear in 155k miles!

Hilton

Oh.. before someone points out - there is an error on the page o the WSM the image is from. In point 5, there's a misprint where they refer to the bearing preload as 0.03mm. It should in fact be 0.3mm per the example given, confirmed against earlier pages in the WSM for earlier cars.

Vilhuer

I measured two diffs wrong way round during winter. One has been run so far without any issues. Another gearbox is still wainting to mounted. I would be surprised if it makes any difference which side is used when shim thickness is calculated as long as its done correctly.

Only difference I can think of is that WSM style puts lighter end of diff to side which is not solidly mounted to diff housing. Maybe that makes some difference but it can't be much.

Hilton

Thanks Erkka.

The weight of the crown wheel did strike me as being relevant, but the difference should be measurable using feeler gauges on both the top and bottom of the opposite side plate, to verify that the diff is being held horizontal.

Any thoughts on measuring the gap with the diff carrier assembly complete (including crown gear and speed sensor wheel), and the pinion in place?

Vilhuer

Thats exactly what I did. Just another end compared to WSM. Did it before and after R&P swap. Around 0.05mm change with new bearings on two separate diffs IIRR.

Hilton

The inner paranoiac in me has reworded the question Erkka replied to above to make it more explicit.

Given the risk, I'm going to do it both ways and compare results.. so even if I have to do the more laborious way and risk busting up the diff carrier bearing, I can at least provide a measurement that answers the question, and may benefit others. (taking photos - will attempt a write-up for diff swap to LSD once its running)

Looking forward to driving my '89 with a LSD.. my white '87 has one, and its a big difference.

Leon Speed

So Hilton, how did this work out?

jon928se

He's yet to find out. Something to do with a new 87 arriving meant the old 87 needed to be prepped for sale getting in the way of putting the 89 back together.

Hilton

Hi Aryan - I ended up doing the measurement both ways. I.e. once with no crown wheel on the diff, and measuring on the factory-specified side, and then again once installed with the crown wheel in place, and measuring on the right-side of the car. Both measurements were identical, so in my opinion it is fine to assemble the diff completely including ring gear before measuring the gap, and if I ever have to do it again, I'll just do the measurement on the opposite side to the WSM.

I have the pics on my desktop PC - haven't put them together to start a write-up yet, as the car hasn't been driven yet - it currently has no brakes on it. Will have a look later when I'm not on the laptop to see if there're any other useful bits I have photos of.

Leon Speed

Ok thanks! No hurry, doing some research for a coming project