Diff output flange dimension request

Post Mon Jul 02, 2012 4:40 pm

If somebody has a medium case diff handy I'd like to request a measurement. I want to know the face-face dimension of the output flanges, i.e. exactly how far apart are they?

Am I right in assuming that all medium (and small) case diffs for the E30 should have the same dimension between output flanges?

Are all E30 medium case output flanges the same?

The reason I ask is that I have two medium case LSDs and one has very short output flanges, such that the ends of the driveshaft bolts nearly touch the casing and the other has quite 'sticky out' flanges more like those on a small case diff.

The diff with the taller flanges is currently fitted to the car, it fits fine but I can't help wondering what effect this will have on the drive shafts. Obviously they are designed to have some compliance in length for suspension movement but how much? If they have been bolted to a diff with taller flanges will this cause damage to the CV joints?

Thanks

Post Mon Jul 02, 2012 4:54 pm

Medium case diffs were also fitted to the wider E28...
E30 fit one's have the thinner output flanges.These are just a 'snap fit' and can be swapped around as required.

You are correct in assuming that both small and medium case diffs for E30 will measure the same across the output flanges.

Post Mon Jul 02, 2012 5:12 pm

This is the one fitted to the car currently - taller output flanges

The 4.10 in this picture is what was on it previously - shorter output flanges

I haven't yet been to measure them again but there is probably 10mm difference each side if I was to have a guess.

Which one (if any) is wrong?

Post Mon Jul 02, 2012 5:32 pm

For E30 fit you require the thinner flanges for the medium case,and the thicker one's for the small case.

A pair of long screwdrivers behind the flange will pop them off,they are simply held with a snap ring.

Post Mon Jul 02, 2012 5:35 pm

Would you say then that the flanges in the top picture are the wrong ones for an E30?

Post Mon Jul 02, 2012 5:57 pm

MrWhite wrote:Would you say then that the flanges in the top picture are the wrong ones for an E30?

They look like the thicker one's to me,in your second photo,the outer one's have thick flanges and the inner pair have thin one's.

Assuming that the diff photo'd on it's todd is a medium case(8 bolts to the rear cover)it will need the thinner flanges.No idea if using the thicker one's will bugger the c/v joints,but I would think that it will affect suspension movement.

Post Mon Jul 02, 2012 7:05 pm

When folk talk about thinner flanges are they actually referring to the material thickness of the piece the driveshaft bolts to or do they mean the height (distance of face from diff body)?

To me the four diffs pictured together are of the same type i.e the face to face flange dimension is the same. The thickness of the actual flange perhaps being a variation. They are very different, however, from the one pictured top.

Could somebody post an image of a medium case fitted to their E30. Does anybody find that the driveshaft bolts seem almost too long?

Post Wed Jul 04, 2012 10:07 pm

Can anybody else comment on this matter? I need to know whether the diff I have fitted to my car, with the taller flanges, is likely to cause damage to the driveshafts because of this. It appears to be running fine albeit a bit whiney. What noise do f*cked drive shafts make?

Post Wed Jul 04, 2012 10:24 pm

your f**king your diff if not f**ked already and not the shafts they knock. but give it a while they will with that setup

Post Thu Jul 05, 2012 5:49 pm

Great news, bluntly delivered. Thanks. I now need to find out how a pair of output flanges from a small case diff (?) found their way onto a medium case.

What do you mean when you say the driveshafts knock?

Can anybody tell me the dimension I asked for in the original post? I want to know what the difference is that I am running.

Post Thu Jul 05, 2012 5:53 pm

if the drive shafts have gone you'll know it

Post Thu Jul 05, 2012 6:08 pm

I've guessed that bit. I've not had any other indication that things aren't working right other than a whine from the diff (no worse than I've heard on other ones). The car drives fine. I'd have thought that if the driveshafts were running at the limit of their longitudinal 'float', due to the wrong output flanges, I'd notice some sort of protest from them as the suspension travelled past the in-line point of the axle. If that makes sense...