christallon

Hi,

I just purchased a rebuilt factory G50 2 plate LSD from Carquip at the LA Lit show this morning. The number stamped on the side is 947 ZF. The unit was rebuilt to a 50/50? at 15 Lbs of pre load (I think) The tag said 993 next to G50 (see pic below) but I was told it would work in a 964. I have done a pretty extensive search through the archives here and discover very little info relating to the 50/50. I assume this is a 40/40 unit that was rebuilt to the 50/50 spec, although when I bought the unit this morning I didn't know enough to ask.

Is there any way to tell from the attached pics if this is indeed a later LSD, and will it fit into my G50/03 trans? Are there any mods I'll need to consider prior to attempting install? It looks nice and clean and sure looks fresh. Thanks for any guidance...

christallon

Here is another pic:

Steve Weiner-Rennsport Systems

That will fit your car, no problem.

If it were me, I would measure the preload before installing it so you get an idea about what to expect. At 50/50, I would anticipate additional understeer, at least until the plates wear a bit (that won't take long with the 2-plate units).

christallon

Thanks Steve,

According to Tom at Carquip, the preload is 15 Lbs (I think). The tag says 15 Lbs, so hopefully that's what it means? Is 15 lbs OK?, and how would I measure it prior to install? Is this indeed a 993 2 plate LSD then? I read the 993 has a larger housing, so I assume there is space where the open diff is now to accommodate that. Will my mechanic need any other parts or special instructions to fit it properly?

Many. many thanks Steve. You have always been very helpful to answer guys like me here on Rennlist with many questions. Much appreciated.

Chris

GTgears

The 964 and the early 993's used the ZF LSD. It wasn't until midway through the 993 production that they switched over to the larger bodied LSD make by GKN. That LSD will fit in your car with no problem.

To be perfectly honest, if that LSD is fresh at 15ft/lbs I wouldn't be calling it a 50/50. In my book that's a 40/40 LSD still and hasn't been upgraded or improved at all with those kinds of numbers. That was never a particularly high preload LSD to start with, but 15ft/lbs is not aggressive by any measure.

christallon

Thank You GT Gears. Appreciate that. If I were in Colorado, what would you charge to install the ZF, and would you do it with the trans in the car, or would you pull the trans down?

Thanks again...

GTgears

We don't do installations. I would send you to Carquip for the installation if you were in Colorado.

christallon

Thanks for the input. Anyone else with an opinion on this? Is the 50/50 increased from 40/40 through adding pre-load in a 2 plate LSD, or is it arrived at with different friction plates and washers? TIA :-)

ilko

Chris, to properly install that particular LSD you will need to drop the transmission. Each unit is slightly different and you need to use shims to get it to fit perfectly inside the case. That's why the tranny has to come off. If it was the original LSD that came with the car, you can take it in and out without removing the tranny, but since it's a different unit the transmission have to come off.

GTgears

This is really a question you'll need to ask directly to Tom Conway to get the answer with respect to your particular differential. The reason I say this is the old opinions are like a-holes adage, and when it comes to differential tuning, even experts will often disagree with what they like in a diff. What Tom calls a 50/50 set up is something I may or may not agree with in theory. Without pulling the cover and knowning exactly what's inside of that particular unit, I wouldn't be able to give you an informed opinion on what is going on.

Theoretically, with respect to your question, if you haven't already understood this, the answer is that people make a differential more aggressive both ways. Oftentimes, when someone rebuilds an LSD with our components, they will use a thicker belleville washer than was stock, thereby introducing more preload onto the differential. This is secondary to whether or not they actually changed the plate configuration. While Porsche originally designed and sold that LSD as a 2 plate (one friction disc per side) LSD, we do make thinner plates for it that allow you to stack it up to 4 plates. This is a common motorsports configuration that is used by Club Racers on RSA's, that used that diff originally.

However, when they go 4 plate with it, regardless of belleville washer choice, I rarely see the breakaway test on the bench deliver anything less than 40ft/lbs. Just by doubling the number of friction faces, the bench test numbers pretty much double or more. Given the low numbers on this unit, I suspect Carquip rebuilt it as a 2 plate unit. Whether they used OEM parts or our parts is something that only they can tell you or you can discover by pulling the thing apart and looking inside. If you did that and posted pictures, I could give you a more concrete answer about your LSD versus just speaking in vague theoretical commentary.

christallon

Is it simple enough to pull apart, ie) no special tools, tension release etc. to deal with? The curious person in me would love to look inside, but I'm practical enough to know that if there are tricks and knowledge required, I'd probably shy away. I can see two allen screws bolting the closure plate to the housing. Is it easy enough to remove these 2 screws and start pulling pieces out to photograph?

Tom did state it was a 2 plate diff. I'll call him now to see if he remebers if the washers or plates are Porsche originals or from an alternate source. Thx

Thanks Ilko. I guessed it would have to come out. I was quoted 4 hours by Aase Bros in Anaheim, but I think they figured they would leave it in. Does 4 hours sound right including removal and re install of trans?

KaiB

Chris, do so. You're not taking a watch apart, or for that matter, rebuilding the recoil spring on a lawn mower (!!!). Nothing will jump out when you break it open.

ilko

Not at all. More like 8-10 hours. Best of luck with the install, if you have an open diff now, you'll love the LSD!

christallon

Yup, Open dif now. I like the LSD in my 73, so I'm looking forward to refined performance in the 964. Appreciate the heads up too Ilko. I'm going to call around today and get a better idea.

GTgears

I would trust the Jeff and Alan at Aase to do the installation with the gearbox in the car. That approach is not for everyone, but a good mechanic who does a lot of this kind of work can absolutely do it and do it right with the gearbox in place. It's easier to take the measurements with the gearbox on the bench but it's not 100% required.

As for your other question, as was mentioned, it's not a Swiss watch. You can pull that thing apart and look inside. The one thing you need to be aware of is the end cover on that version LSD doesn't come off very easily. There's a huge step that goes up into the body of the diff an inch or more and it tends to hang up on the body a bit. It takes a little manipulating to get it to come out, but once it does, it's pretty straight forward from there.