drnick

interesting thread as im having the lsd out of an 86 auto transmission rebuilt at the minute to swap into my GTS 5spd box. i will have to see about modifying the pinion shaft - how much do you take off it steve?

also a question to erkka: can i re-use the existing GTS oil pump without difficulty? i had thought it would be necessary to fit an external electric unit, my mechanic has also said the inbuilt ones might be more prone to failure.

John Veninger

Gregg wrote:
They are there every time I look
I'll email them to you directly if you like.

Dennis K,

I've come up with a plan to add two additional friction plates to the unit I'll be installing. Details will follow once I buy the new plates and do the install. Can you let me know why your's failed with the additional lock? My friction plates were also completely stripped, but there was a whole lot of failure going on inside there!

Vilhuer

Manual GTS mechanic pump is "easy" installation to PSD diff as those have threads in them for 80+ teeth pump rotation gear. I suspect same gear is possible to install into LSD diff also in place of speed sensor magnetic wheel with some modifications. I can't see any mechanical problems in Porsche pumps any more than in 928 engine oil pump has problems. On contrary, as long as screen keeps out large pieces of metal from the pump it should work for very long time without needing any service. Mine has close to 100k miles and it feels fine. Pumps two shaft ends are visible on outside and bearings seem to be ok when they are rotated. Haven't opened pump completely yet though so can be sure there isn't anything nasty waiting inside.

drnick

cheers for the info erkka

Steve Cattaneo

With a flat spot under the gear, the pinion gear receives lube oil as they turn on the pinion shaft, a simple modification would have prevented the failure that John experience. The depth of this Factory pinion shaft was .080

John Veninger

Thanks Steve!!!!!
Wonder why that isn't a standard

I'm going to cryo/rem a few transmission gears. Any reason not to have the spider gears done?

Here is a picture of the gear set not destroyed.

drnick

steve, ditto on the thanks expressed above! the pic makes it perfectly clear

SteveG

As an aside, John, at FarnbacherLoles I mentioned there was an LSD on ebay. I guess you might have bid. It went for $400.

John Veninger

Nope. I have owned a spare LSD (actually a complete 84 trans) for the past 3 years.

$400.00 is a good price.

Glen McCartney

Nick, sent you a PM.

Glen

Carl Fausett

John - perhaps I had the good fortune of getting off the track pretty soon after it happened so there was not quite as much chewing.

Our best guess is the cross-pins (#3) break first, the fact that they are ground in half like lincoln logs gives them a natural fracture point.

Then, once the bevel gears are loose, they are free to climb axially and move about.

I cant quite tell from the photos - is that a 20% LSD you tore up? Mine is (pictures below).

Lizard928

What about instead of having 2 shafts that are notched to fit together, make them out of a single billet piece?

Carl Fausett

They did something like that in the later PSD differentials, where they have a single cross-casting in the center. You can see its much stronger.

We are going this way: I heard from 928 Intl that the "hot setup" was the early (78-84) 40% Limited Slip was better than the Late-Model 20% LSD. 4 frictions disks instead of two, and we can also see it has a stronger core.

Problem is the size difference - the early LSD is wider than the late-model one, even after you transfer the ring gear over.

We took both to a CMM (Coordinate Measuring Machine) and had them carefully indexed so we could accurately locate the ring gear on the 40% LSD unit.

What I've done is make a large spacer to adapt the width of the 40% LSD to the late-model case. Photos below. If it works, you end up with the best of both worlds: the Borg-Warner transmission with the 40% LSD differential.

We even learned that you can re-stack the drive and driven plates in the LSD in a different order than they are now, and you would double the surface area available to the, and raise the LSD to 80% if you wanted to.

They are currently stacked drive plate/driven plate/driven plate/drive plate; and by restacking to drive plate/driven plate/drive plate/driven plate you have the same final assembled dimension, but twice the friction surface.

I left mine at 40% however, because of the 180 and 190 degree switchbacks at Pikes Peak - where I thought the 80% LSD might be too much.

I'll post again if it works - trying to get to at least a DE day or something with this LSD setup before the snow flys.

Vilhuer

Carl, what makes you think later style LSD is 20%. AFAIK Porsche calls it same 40% like all 928 LSD. AFAIK number of plates do not mean how much force is transfered. Many BMW have 25% LSD which would be impossible to have if each plate adds 10%. I think % is determined by style of plates and how tightly they are packed.

John Veninger

The very early LSD were up to 80% while the newer style ones were 40% from what I recall.