Don Nguyen

Trying to do some research here on what needs to be done and what the options are to add/convert an open diff C4 to one with an LSD.

Thanks.

-Don

alexjc4

Rear diff? Not done it myself but I had my diff out recently and it looks fairly easy. Remove the PDAS slave cylinder and block off the opening in the gearbox/diff case. Then when you have the diff out remove the lever arm that the slave pushes against the PDAS diff clutch pack.

freedman

Does the c4 awd system not act as an LSD anyway?

Andy Roe

That's what I thought too. An LSD is essentially a mechanical traction control device, and the C4 AWD system will do the same automatically if it detects wheel slip.

Ghia

Are you spinning rear wheels?

If so, maybe have someone check out the state of the VC to see if it's functioning properly before adding an LSD.

The 964 has a fairly complicated 4WD system unlike the 993 and later which only transmit up to 40% or so of drive to the front wheels.

MG

FeralComprehension

It does. Locking proceeds in stepwise fashion if wheelspin or yaw occurs (unless you're on the brakes; PDAS action is halted to keep the ABS system free to operate).

IIRC C4-based race cars of the era replaced the computer-controlled valve hardware with a setup that allowed the driver to regulate the degree of locking by twisting a **** that applied pressure to the locking actuator.

deutschland-dobson

Is that the system that the C4 Lightweight has then?

Don Nguyen

I never knew/realized that the C4 system did that. I've had my Porsche for 6 years now, but I am more of a BMW person, so I feel like I still have so much to learn! haha.

How hard/easy and expensive is it to change gear ratios in these things?

PAOLOP

How hard/easy and expensive is it to change gear ratios in these things?[/QUOTE]

It's almost impossible!
No one make gear ratios for a C4 964

Paolo

Bill Verburg

It's almost impossible!
No one make gear ratios for a C4 964

Paolo[/QUOTE]
and no ones makes an aftermarket LSD for them either

if yours is no longer working you will have to take it apart and rebuild the oe LSD w/ factory parts(if they are still available)

alexjc4

A mechanical LSD will lock based on load, it won't wait for differences in wheel slip rates or Gs. So it will behave differently than the PDAS controlled diff.

The factory LSDs vary depending which one you have but they tend to give quite strong deceleration lock up, which is good for braking. As said above the PDAS opens the diffs on the brakes.

The C2 uses the same case for the diff doesn't it? C2 even has a blanking plate where the slave goes on the C4. This leads me to think the dimensions of the diff itself are the same C4 vs C2. The c4 just uses a different mechanism to compress its clutch pack. Bill, you may have seen the diffs side by side so you may be able to rule this out though.

Bill Verburg

964C4 oe lsd bears absolutely no resemblance or kinship to 964C2 lsd, they don't eevn share any of the same parts and are not in anyway interchangeable.

They are however both clutch plate type lsd's, the 964C4 contains a single stack of 7 internally splined and 7 externally splined friction disks which are probably going to be more effective when new than the C2 which uses 2 stacks of 4 disks(2 internal and 2 external)

alexjc4

the ring and pinion look the same (pn 964 302 911 05 for G64 and G50) as do the bearings and that's what counts surely?

obviously the diffs wouldn't have any interchangeable internal parts.

Bill Verburg

some people have supple imaginations if you think that the cwp is part of the lsd then who am I to argue

alexjc4

Ok, what does the diff bolt to?