The Workshop manual refers to both the early and the late LSD units as "40% lockup", but the early LSD has 8 friction discs where the late model only has 4. It was Mark Anderson who told me that the late model LSD units weren't very good for racing - the early ones hold more torque.

And, like John says, we see how to re-stack the plates in the early unit to 80% lockup if we wanted to.

I may have errored at calling the late model ones "20%" but I wonder what they are if the early 8-disc units are 40%.

 

all i know , is that under the most demanding LSD turns like at Sears turn 2 (off cambered right), the 87 limited slip kind of fails. at most all other turns, it works fine. (bad at thunderhill turn 6 off cambered right). I measured the LSD force and its near 25ftlbs max . a locker will be useful there, but can introduce wheel spin and looseness. I think anderson is using the early LDS with more intermal grip.

 

Carl,

There were three physical different size lsd units, 77-82, 83-89 and 90-95.
In the 83-89 the internals had different plate configurations. An 83 to ?? used an extra internal metal spacer plate. I was able to add an additional disc in place of that plate to create more lockup since any other machine work on the hardened steel is beyond what I was willing to do. You cannot do that with a later year "83-89" unit.

I knew someone who did machine down a 77-82 unit to put into an 87 since the earlier units had more lockup.That is a bunch of work and needs precise machining of hardened steel. He told me wouldn't do it again.

 

This is a cool thread folks. (With the exception of the LSD snuff-****...)

JV - good luck. Don't break anymore parts man!

Greg, I think you have to be logged-in with your user name and password to get the pictures.

 

DC,

This is an old thread. MY LSD was fixed last year and has held together this year!

 

I knew it was an old thread. But, damn, I missed a season?

 

Thanks John, Good info,

I'm trying to devise a way to insert the early LSD into the late trans without milling hardened surfaces... I think I can do it. The early LSD is relatively easy to locate (much more so than a late-model LSD) and seems to hold more torque according to other racers.

I hope you dont mind I added on to your thread. Seemed wise to keep all the info in one thread rather than start a new one as your LSD failure and mine were identical.

 

I hope he doesn't mind either. Good to keep it all in one place, for those watching from the sidelines

 

Why would I mind?? I enjoy sharing what I've done or learned. Kind of why I'm on the PCA Tech Committee.

 

It is actually easy to machine. Fairly cheap too. The real problem is that the flange that carries thering gear is thinner than desired.

 

Steve Cattaneo's diagnosis seems to be spot-on. We examined the 4 spur gears on the fragments of the crossshaft that remain, and one is so severely seized that we could not even nock the shaft out of the gear with a large hammer. Friction-welded, it would seem.

I have ground the flat into the shafts as shown, makes sense to me, we'll see what the results are.

 

The flange that carries the ring gear is twice as thick on the early differential as the late-model diff.

 

Working for me so far. Also cryoed all of the internals on the trans and diff.

 

By JV
I have done this also, I didn't machine the flange due to potential distortion issues, i.e excessive runout. What part did this fellow machine? My runout ended up at 0.02 mm. Something I could live with, as I didn't rotate the crown wheel, I don't know whether the runout was in the area machined or the crown wheel. I did have to buy new bolts, they were expensive. Those bolts get done up real tight, they almost strip in my opinion.

I wouldn't run a 80% locking diff on the street if I was to pull the box out for any reason I may well go back to the standard 40%. As long as you don't hammer it around corners you get away with it though.

Greg

 

Greg,

Found the old email from 2002 on what he did. This is all the details I have since I never went that route.

It is not very simple. You have to machine the ring gear, which is
hardened steel. Carbide lathe tool, many hours of small cuts to take
off 2 mm. Unless you have a lathe, it's cheaper to buy the late lsd for
$1200 vs $500 for the early than to pay someone to machinge it. Sell
your early lsd and save the headache.