Evan, the axle flanges "bottom out" on factory differential housings by design, so that they don't on the differential internals.
As long as the flange has axial movement, there is no problem in "bottoming out".

The Carrera differential in the illustration above was introduced in the 85 model year. It had a cast iron housing with large elliptical openings, and one coated inner disc per side (two total).
The pages below are from the 85 Carrera Service Information manual.
From what little I can see in your photos, you have an earlier multi-disc differential.

http://forums.pelicanparts.com/uploa...1514398007.jpg

Thanks so much Jon!

This is great info. It sure looks like i have the earlier diff, I guess this means 2 plates and 2 discs per side. And per the earlier diff specs I am below breakaway torque, so it is time for a refresh.

All further tips greatly appreciated.

Evan, the result of your test is still acceptable for a road car.
If you want to rebuild it, then check on the price and availability of new discs and plates before you open it.

If you decide not to open the diff, you should still torque the ring gear bolts to spec, to make sure that none are coming loose, and replace the lock tabs.

Great tips, and things I hadn't thought of at all.

I'm considering opening the diff if I can get all the parts, as I've put so much into this box already it would be a shame not to bring everything into spec. I have to admit though that it is tempting to leave it be.

Can anyone help with part numbers? I think that the discs are 917.332.552.12 but maybe someone can confim. I can't find the plates. And what about belleville washers and thrust washers?

Here are the part numbers for an SC multi-disc diff, from the 83 911 PET:

928.332.551.00 ... Inner Disc 2,0mm
917.332.552.10 ... Disc with External Splines 1,9mm
917.332.552.11 ... Disc with External Splines 2,0mm
917.332.552.12 ... Disc with External Splines 2,1mm
930.332.553.00 ... Lamina 1,4mm
928.332.555.00 ... Cup Spring
901.332.561.11 ... Thrust Washer

The discs with external splines (tabs) were available in three sizes.

Super! Thanks!

I believe with the reissued Parts through Classic Porsche only the 2.0 friction is being reproduced.

The 2.0 mm clutch disc 928-332-551-00 remains available, just received a bunch. I've been using them for years in the 944-series boxes too, since Porsche made their 2.0 mm discs NLA, 917-332-551-00, and there's no real difference in the parts. (Felt to me like Porsche wants the 944 guys to upgrade to the 2.50 mm clutch discs plus the corresponding pressure rings, but it's pricey.)

FWIW, I checked Polaris stock on the 2.10 mm outer discs a few weeks ago. PAG has like 600 in the warehouse. Too many surprises recently...

Catching up on this thread, I saw a question about bearings from LDT. I don't know them, but just got a 930-302-391-01 from Porsche marked "LDT/P." So I am thinking they're legit.

Happy new year to all!

Pelican lists all these parts as either in stock or available by special order except the cup spring. What is a cup spring?

I'll get my diff apart and see what is in there, and what shape it is in. I have so much effort and $$$ in the box already, so why not just go all in.

Kevin, thanks for the feedback on the LDT bearings. I'm pretty sure that TwinSpark wouldn't use them if they weren't up to par. I hope I don't eat those words later.:rolleyes:

Cup spring is what they call a Belleville washer. Kevin’s part number is correct for the clutch.

Evan, the "Cup Spring" is the conical spring that provides pressure and preload to the differential clutches.
The item descriptions in my list are those used by Porsche at the time.

Moving right along! While waiting for parts I've been cleaning up my engine bay and tearing apart my steering rack. I've got the diff apart too, if you ever wondered what the guts of a limited slip diff look like here they are. New friction discs and steels are in the mail, so I should be able to start reassembly soon. Fun stuff!

http://forums.pelicanparts.com/uploa...1516140125.jpg
http://forums.pelicanparts.com/uploa...1516140125.jpg

It's a multi-disc diff, but with only one friction disc per side.
Was one plate per side a 1,4mm Lamina? These are listed in the 83 SC PET, but your car is an 81 SC.
Did you purchase the diff parts from Porsche, or elsewhere?
When you receive the new parts, please post photos of the part number labels, they should be dated and indicate if they were manufactured recently.

I have no doubt they were manufactured recently. ZF has continued to make these clutches all the way through the years and if you open up a Drexler aftermarket lsd you will find them inside.

Nice LSD!

How's the ITB transformation progressing?

Parts arrived and I've got the diff back together. Jon: yes, the outer steels (against the Bell washer) are the 1.4mm lamina. I've re-used these, and also the thrust and Bell washers. I've reassembled with new 2mm steels and friction discs, 2 per side this time.

I used Paul Guard's guide which made the teardown and rebuild easy. Though his post shows a Carrera diff, the concept is the same. Every part went back in loaded with Kendall dino oil with the LSD additive. Breakaway torque tested at 47 lb-ft after rotating the diff a few times to get all the parts settled in. Well in spec for this diff, and on the low side of spec considering I've got two friction discs per side. Paul's LSD rebuild guide is here.

The steels were made in 2015, the clutches in 2004! Porsche original parts as you can see. I guess Porsche doesn't sell a lot of friction discs around here...

http://forums.pelicanparts.com/uploa...1516400474.jpg

Thanks! The slippery slope is proving frictionless, and on the way to starting the ITB install I've completely cleaned up and resprayed my engine bay. Full fuel line replacement is happening next, and once the gearbox is done and off the engine stand the motor will go on there for the ITB work.

Full fuel line replacement done today, so its back to the diff!

I've got the ring gear back on and torqued, so its time to put all the new lock plates on. I can't find a guide anywhere on how best to do this, and while it seems straightforward I could really use some tips. Can anyone help?

Here is how they looked before I dissassembled:
http://forums.pelicanparts.com/uploa...1516480080.jpg

Evan, thanks for posting these photos. Were you told that everything was available?
You might find that an 80% set-up, with 2 friction discs per side, is a bit harsh for normal driving, but maybe your road conditions require more traction.
If you also purchased new ring gear bolts, I'd be curious to see what you received.

OK, you just posted the last photo a few minutes before my question.
It looks like you re-used the old ring gear bolts?