Heirsh

Mine doesnt make any noise and it works as far as I can tell. 90 model, stock optional lsd. 114k miles. It could have been renewed at some point, but I have the complete records and I havent seen anything about it.

SimonExtreme

I cannot comment on the noise element other than to say I have only ever heard this noise on an LSD car. It is also there on GT3's (from new).

I don't know about the difs being the same in principal, but the "standard" 964RS LSD is a 20-100% one.

Oddjob

The standard 40% LSDs in G50-03/05/05 transmissions use a lot of 928 and 917 part numbered components - which is very similar to the 944 units.

The 20/100% LSDs in G50 -10/52 transmissions use all 950 based part numbers, so although the design is the same, almost all none of the parts are interchangeable with regular 964 C2 LSDs.

911addict

What is it i'm looking for?
If you rev too hard, the back goes, LSD or not....

JasonAndreas

If your 964 has either of the two standard (40% or 20/100%) clutch disc based limited slip differentials you shouldn't be hearing any noise from them. If you are hearing a noise then most likely you have the wrong type of transmission lube. This was a common problem when the MY91 964 Turbo came out and the solution is/was to use an LSD additive or change out the gear lube to something more compatible. You can buy a pint of LSD additive for $5USD from any GM/Chevy dealership.

It depends on the model year; MY90-91 C2 had the 40% as M220 and for MY92+ it was the 20/100%.



The reported mileage on Rennlist seems to be all over the place depending on usage. Some have lasted past 100k miles while others are wearing out in 50k. For the 993 Porsche halved the number of friction discs and that seemed to dramatically reduce the lifetime of the LSD with some wearing out in as few as 10k miles (obviously driver dependant). To check the discs you can pull the axles, lock one flange and then rotate the differential with a torque wrench. The spec for a 964 is 10-35 Nm (7.5 - 26 ft.lbs).

SimonExtreme

Jason

It's not often I have the opportunity to disagree with you and be on strong ground but having driven or been in numerous 964RS's, I have never come across one that doesn't make noise at low speed. This is even reported in magazines at the time the car came out so that would mean that Porsche was using the wrong lube. The level of the noise can change with the lube you use and maybe, on a standard C2, the soundproofing means you cannot hear a properly lubed LSD but I can assure you that with the lack of soundproofing on an RS, you certainly can. You should hear how loud it is in a stripped out clubsport or cuppie!

You also hear the same diff noises, from new, on GT3's. This has recently been illustrated by one of the UK GT3 fraternity changing their LSD to a new Plasma Nitrided Motorsport one and one of the things he reports is that the LSD is now totally quiet. Others on the forum he reports that on wonder whether that is a benefit, because they like the noise!

JasonAndreas

Yes and there might be a TSB covering this with the suggestion to use an LSD additive to quiet the noise? (I don't have the TBSs that were originally published for the Turbos) Porsche eventually changed the inner disc friction material from Gylon (carbon) to Valeo (graphite) possibly for this reason.

The level of sound-proofing in an RS-A is equivalent to that found in the RS Basic and if your RS is stock then my RS-A has even less.

The factory fill for all 996 transmissions is Mobilube PTX and the motorsports standard fill is Mobilube SHC (#999.917.062.00). Depending on who did the install they might have followed the Porsche Motorsports recommendation? I've never used PTX so I'm not sure how much of a difference it would make and I don't remember having seen anything in the GT3 forums where an owner had changed just the fluid?

SimonExtreme

I don't understand what is going on here because I have been doing some checking.As I have said, every 64RS I have been in has sounded the same and 996 GT3 owners report that they heard their LSD's from new and still do, even the only one I can find that is still serviced by an OPC! I also have the bills for all my car's services since new. For the first 8 years, they were done by OPC's. Since then, the car has been looked after by 2 highly respected aircooled RS specialists. I cannot find on a single invoice a charge for LSD additive. Are all these specialists getting it wrong? Maybe it is a regional thing.

I know this is OT, but out of curiosity, what have you taken out that I have?

JasonAndreas

I've made the same suggestion to British based 964 Turbo owners (same LSD as the RS) that complain of the noise after a lube change and they've all reported back with no noise after changing the fluid to something more compatible with the LSD and/or adding a friction modifier. I will try to get my hands on the LSD TSB.

The only thing I can say is to give it a try, it shouldn't cause any problems for your steel syncros?

I removed the rear-luggage dump and because of a leaky windshield I had to remove the sound-proofing/wet sponge that was under the driver & passenger floor mats. But the biggest noise increase came when I accidentally removed the 3" rubber cap on the transmission tunnel (just behind the parking brake). It's still attached but not sealed as it originally was which is something I really need to fix. The workshop manual instructions don't mention in the engine removal section that the bolts behind the cap only exist in the C4.

pncarrerars

I am using Mobilube SHC in my 964 RS & the diff is just as noisy as ever. I cannot believe that this type of LSD is ever quiet unless worn out.

Pete

Laurence Gibbs

I think all the lube change does is quiet the diff. There is no difference in the diff's abilities to do it's job. The noise is normal on RS models with the standard lube. I thought there were specific reasons (can't remember what) for not using friction moddifiers in our diff's?
It does seem strange that almost all the RS owners I know and cars i have driven have all had diff noise.

SimonExtreme

I was looking at my records again, to see what has been used on the car and the most interesting thing is that the gearbox oil got changed by 2 different specialists who have recorded the work being done but have forgotten to charge for the gearbox oil! One of them was when the LSD was rebuilt so I know that they didn't forget to do it! The PO was obviously a lucky man as that sort of thing never happens to me. However, if he saved £50 in the 4 years of ownership, good luck to him, particularly as I have benefitted from the £14,000 he spend rebuilding the mechanical side of the car

JasonAndreas

Well that answers half of it, so much for SHC.

I really don't know anything about tribology so I can't say one way or the other if a friction modifier would hurt the steel syncros in the RS transmission. I do know the turbo has the exact same LSD and adding a friction modifier gets rid of the noise. Hopefully something will be written in the TSB or someone else will know.

Sal 965

Doh,

Another £500 then!!