samluke

I have tried search but can't find what I am looking for.

I am rebuilding my AOR LSD. Anyone know or is prepared to share the tweaks to increase/maximize/optimize the lockup, using stock parts. I have lots of plates to select from.

PM or email samluke@sbcglobal.net

TonyG

I know it's not the answer you're looking for.... but a guard gt 50/80 diff is the way to go (unless you have some class rule that prevents it). It's worth every penny.

TonyG

Oddjob

Now what did you break?

Email with BS and nonsense is on the way...

PorscheDoc

Tony here are how the rules read for PCA.

"Any limited slip differentials (LSDs) derived from a mechanical type that was delivered in a street-legal Porsche is allowed."

TonyG

Then Sam has a green light.

The Guard GT is exactly that...

Sell the stock LSD. Get a 50/80 Guard GT. You'll knock your lap times down for sure.


TonyG

PorscheDoc

Richard,

Didn't Jeff Knight shim the diff up in his GT car?

samluke

Jim,

For once my car is not broken. I had a bad wheel bearing that I changed and a weeping tranny drive flange seal. This LSD has never been apart, so I figured it was a good time to take a look and change. I have a bunch of spares so can build up a different clutch pack.

Tony,

Your absolutely right the Guard is the way to go, but right now I don't have the budget or time. PCA changed the rules so they are allowed now.

Karl,

Yes Jeff did shim his to change the pre-load, but despite what many think pre-load doesn't do much on the lockup, there has to be a change in the internals or the ramp angles . I have some hints and tips from others so I will figure something out.

TonyG

It's in the ramp angles for sure, but aren't the AOR LSD's setup for 80% lock?

Given this, the most you could hope for would be to increase the angle on one side of the ramps which would increase the lock even further on either acceleration or deceleration (depending on which side of the ramps you widened the angle on).

But, and I'm not sure of this, I thought that the ramps on the AOR were set to 80% on both side (both set ramps). And if this were the case, the most you could do would be to cut down the ramp, increasing the angle, which would either bring up the acceleration lock or deceleration lock (or both) up from 80%. But that's not what you want to do. You want a a lot less lock under acceleration. Given that you can't "build up" a ramp (not reliably anyway), and the fact that you don't know the exact ramp angle, I just don't see how you could keep the 80% lock on deceleration and decrease the lock on acceleration.

TonyG

samluke

Tony,

Unfortunately not. All the street 944 Turbo LSD's are 40/40%. Some of the factory race cars got 80/80% but it seems to be a black art as to how they achieved it.

TonyG

Ok. I'm not sure. I thought I had read different... but it's been years.

Anyway, assuming it's a 40/40, you could cut down (increase angle) of one set of ramps to increase the decel lockup (which is what you'd want to do).

The big question is what is the magic angle?

You could buy a Guard GT diff and take a look. But other than that you'd be guessing.

My diff is unfortunately installed in my transaxle now. Too bad cause I just took it out of one trans and put it into another.


TonyG

Oddjob

All factory 944 LSDs are 40/40.

Not aware of anyone that is modifying ramp angles on the factory 944 diffs to make them asymmetric. Just adding plates to increase loaded and unloaded lock. But I dont know why the ramps could not be modified, or custom pressure cups made, if you had your heart set on an asymmetric diff.

You would be guessing at angles, so would require some willingness to test. I would think the more gradual the angle, the greater the outward thrust, the greater the lock. The sharper the angle (closer it is to a 90 deg flat) it would lower outward thrust.

Richard, you want to be the guinnea pig?

TonyG

You're correct in that widening the angle of the ramps increases the TQ applied to the clutches.

But since you don't know the proper angle needed to produce x amount of lock, you're guessing.

Not that guessing is bad... it's just the time required to do the job, then pull all apart to keep increasing the angle until you find that optimal angle. That's what takes a huge amount of time.

So the question is... how much is your time worth?

Plus... aside from the locking action of the diff.... the GT is far stronger. I broke a diff 2 years ago. It took out the diff carrier bearings, which moved the diff, which moved the ring gear, which loaded the pinion at a weird angle to the extent that it took out the pinion gear bearing, which then allowed the entire shaft to move, which took out all the gears.

I short.. the trans was destroyed by the broken diff carrier.

yeah... sucked.


TonyG

gt37vgt

well i thought you just shim it more .
be sure when your testing it you use the oil you intend to use ... i hear that redline oil make them more grippy ..

samluke

Shimming does little to nothing, all it does is put more pre-load on the pack. In fact I would argue that too much preload can lead to premature wear. As long as the pack is together its the ramps, geometry and clutch plates that do the work.

In fact there is a mod that results in no pre-load at all on the clutch pack, which is probably the method I will use.

The factory units are simple and effective and last a long time. Same design principles as the GT one etc, just without the options on ramp angles. Mine is just about out, I suspect I'll find it to be in perfect condition with negligable wear despite many years of track duty.

gt37vgt

one suggestion would be have the ramps micro polished and the friction surfaces grit blasted ..but its just a loose theory ..