smyth1

can anyone tell me if the pinion needs to be changed if going from open diff to limited slip.i want to put my original limited slip on a trans that had an open diff.thanks

blown 87

No it does not need to be changed.

Brett928S2

Hi

Ummm thats not quite true...

Technically you are correct it does not NEED to be changed as the pinions are the same...BUT the original crown wheel and pinion have both done thousands of miles TOGETHER and they wear together...

I tried it when I put in my LSD .....put it all back together, jacked up the back end to make sure is was all ok...and got a HUGE whine when revving up....caused by the difference between the wear factors on the two pinions....so swapped to the LSDs pinion and all quiet again...

So personally I would advise you to change BOTH together....

All the best Brett

hacker-pschorr

There is another possibility you did not install it 100% correctly - no offense, it is possible.

I've watched our local guru install an LSD into a 928 transmission. Started with some measurements, a good amount of paint, a few custom shims, and a couple of hours later - it was in.

Some jobs I leave to the experienced, it's just too damn important. Which is why my LSD and transmission are on their way to Todd's house.

Hilton

Brett, you could have just removed the crown wheel off the open diff and installed it on the locking diff. Then work out the diff bearings preload, measure backlash, and shim accordingly so its within factory new specification.

The workshop manual is very clear on the setup and measurements required, and the whole job is actually pretty easy. I added LSD to my 89 manual - works just fine, no diff noise, and leaves two stripes on the road now when I spin the wheels.

Smyth1 - yes, you can leave the pinion in there and move the matched crown ring to the "new" diff.

Glen McCartney

Hacker is right, had a LSD put in mine when had tranny rebuilt, with original ring and pinion. Just have to do measurements and shim as per WSM. Mine was done by Steve Catanneo, leave it to an expert.

blown 87

You use the ring gear off the original trans, at least that is the way I have done it.

Buy new bolts for the ring gear, you may need them though.

Only a idiot would try to mix a used ring gear with a used pinion from two different matched sets, as it seems you tried to do.

Vilhuer

Only idiot would try to mix new ring gear with new pinion from two different sets. They are meant to be used as pair. Factory paired them together and marked best run position. If one or another is changed this info is lost and one has to be really lucky for new pair to have same silent run position as either ring or pinion position was.

Dave928S

Smyth 1... the pic below is what you swap into your case, after bolting the original crown wheel (taken from your existing standard spool that you're taking out) onto that, then go through the shimming procedure to get the correct bearing preload and crown wheel/pinion backlash as per the WSM procedure ... as Hilton has already pointed out. I put new carrier bearings in also. Simple ... and the matched pinion and crown wheel are still matched and will run silently. BTW .. would help everyone to help you if you put your vehicle details in your posts

Brett ... what you said is 'not quite true' ...

Leon Speed

Dave, what year is that LSD? Looks different from mine.

Dave928S

Aryan
Its an early model 40% which would look different than yours in a couple of ways. The later ones have elongated spool holes, which I read in a service bulletin (I think) were increased in size, to allow for greater oil circulation within the LSD case. They're also longer than the early ones, which is why in Carls kit for putting the early LSD's in late cars he's included a billet spacer to make up the distance.

Here's a link to his site showing an early diff fitted to a late case, with the spacer on the right side ........ http://www.928motorsports.com/parts/...er/LSDkit3.jpg

PET doesn't show those differences in detail.

blown 87

Yep

Leon Speed

Thanks. It looked more "modern" than mine, but maybe it's because this was pre-cleaning

Brett928S2

Hi

When I said I changed mine.... it was actually Paul Anderson and I who changed it together...and there is NOBODY in the Uk who knows more about 928s than Paul...

We thought it was worth a try as its only a 10 minute job to try it....we both realised it probably wouldn't work and once proved right we changed the pinion as well...

The point here for the original poster is ....as long as both crown wheel and pinion are matched you will be fine....

All the best Brett

Dave928S

Anyone who is a good mechanic would not do this on any diff ... and anyone who knows 928's knows that ring and pinion are factory matched. It's well documented in the WSM and in service documents.

Why the ***k would you even contemplate doing a backyard mechanic job like that. Its a lot more than 10 minutes to change a diff centre and get bearing preload and crown and pinion backlash to spec ... in other words ... to do it properly.

Why would you change the pinion? I think you have your terminology mixed up ... you take the crown wheel from the open diff and fit it to the LSD spool that you're changing in to the case, and then shim to get bearing preload and backlash correct. You leave the pinion alone.