Refurbish LSD for 993 4S Coupe

[matthewb]

Hi chaps

The thread on LSD http://www.porscheclubgbforum.com/tm.asp?m=737305 got me thinking about the state of my standard factory-fitted LSD. My car's done about 160k miles and my research would indicate the LSD clutch plates wear-out at about 50k.

So I decided to refurbish the clutch LSD (replace the worn out plates). My indie, however, had trouble identifying the correct part number for the replacement plates. Apparently the obvious part wasn't 'tied' to my gearbpox in the PET. So I asked my buddies at Cardiff OPC if they could help. They came up with the same part number and the same caveat/concern.

My indie and I went with part 950 332 983 08 and I dropped the car off this morning. I just had a call from him saying that it's the wrong stuff so unfortunately he's putting the LSD back together with the original worn-out plates.

It looks like if I want a working LSD for my baby I'll have to go for a whole new diff unit.

Any thoughts on what I should do? Does anyone know of a suitable reputable 3rd party LSD diff for a 993 4S? Perhaps not a clutch-based LSD, e.g. perhaps geared, viscous, gerotor etc. I'm thinking of the Wavetrac torque-biasing LSD?

Occasional track use but mainly hard bendy road use.

Thanks.

 

[Mark Elder]

Hi Matthew,
>>mainly hard bendy road use<<
Are you actually getting one of the rears breaking traction in these condition? - if so at what sort of speed (beyond the limits of the ABD?).
Only time I can get it to happen on road it's slow enough for the ABD to catch it.

 

[matthewb]

Hi Mark

I was wondering if you'd be the first (only) person to respond. Many thanks.

In answer to your question - Yes, I have experienced that occasionally on public roads - usually on broken, gravely bits (i.e. all of them!). I'm probably doing about the speed that ABD stops functioning.

But that's not quite why I'm looking to do this. My understanding is that, amongst other benefits, the LSD provides more consistent torque when cornering (helping prevent break-away), enabling earlier acceleration out of a corner. Apparently, you just 'feel' it's OK to go for it, giving you the confidence you don't get with an open diff. The idea, I think, is to prevent the need for ABD having to step-in. I'm just curious to experience an LSD - mine was probably burned-out when I acquired her at 45k miles.

But which one? From what I understand, the main operational difference between clutch-based and gear-based LSDs is that clutch-based LSDs perform well when new but wear-out, whereas gear-based torque-biasing LSDs (e.g. Quaife) don't wear-out but don't do much when transitioning from accel to decel, coasting, or when one wheel has no traction. Please let me know if I'm wrong or have over-simplified.

The Wavetrac LSD, apparently, deals with these gear-based torque-biasing LSD shortcomings, performing more like (new) clutch-based LSDs.

Prices for Quaife and Wavetrac are similar - a possible small cost-saving is not really important to me considering the one-off nature of this replacement.

M

 

[Lancerlot]

Porsche use a standard ZF LSD unit, don't they? I would have thought any motorsport transmission specialist should be able supply and fit a new shim pack for you.

Regards,

Clive.

 

[matthewb]

I'm sure you're right but after the hassle I had over new plates with Porsche and not knowing where to go next, I decided I'd go for something different that wouldn't decline over time and need refurbishing (again). i know clutch LSDs are better than torque-balancing gear LSDs - but only when 'fresh'. I ordered my Wavetrac LSD this morning.

 

[Flightrisk]

Ah Matthew even a couple of months later after first posting I am still deciding what to do about mine.

I agree that the Wavetrac was probably the best option out of all the replacement units; where did you buy yours from in the end? It is still under consideration.

I have also been collecting quotes from Indy garages for the rebuilding of the original, they are to provide the parts so the emphasis and costs are on them to get the correct ones! Tried to get a quote from OPC Byfleet but they have not bothered to reply so I guess even they look at this job with trepidation.

It will be very interesting to hear your thoughts once it is fitted.

James.

 

[matthewb]

I ordered it yesterday - Design911 £1021 + VAT.

I'll keep the original clutch diff so the car can be returned to factory-state if needed. I might even have the clutch plates replaced if I can find what's needed - Lancelot's probably right about ZF.

I didn't keep the old Monroe suspension though. Replaced them with KW Variant 3 coilovers. There're some things not worth returning to factory-state - ever.

I'll post pics of the Wavetrac when it arrives (Monday, I hope).

M

 

[Flightrisk]

A M033 kit was fitted by a previous owner around 5 yrs ago so the handling is not too skittish but I'm still going down the Bilstein PSS10 plus powerflex bushes and RS engine mounts route.

 

[matthewb]

I did Powerflex polyurethane bushes too. I got fed up with the cost and grief of needing new wishbones (with rubber bushes) every couple of years.

I know Bilstein are the 'norm' and I'm sure they're very good, but Ken Coad convinced me to consider KW Variant 3. He succeeded. They really are rather good - the thing that tipped the balance was KW's build quality, especially with regard to rust resistance. Bilsteins did have a reputation for rust. Take a look at http://www.kw-suspension.co.uk/

I had new rubber engine mounts fitted a couple of years ago. I guess they were the 'standard' ones. How do the RS mounts differ (performance and cost)?


M

 

[Mark Elder]

Matthew, it would be good if you could try to conduct a fairly objective before-and-after test - tough I know because the weather and even some random grit on the road can make a big difference. Even a specific piece of road that you know well that you evaluate before and after.

I can see a few of us C4x owners copying you if we hear reports of significant improvements.[]

 

[matthewb]

Just try and stop me, Mark But in all fairness, I guess that despite how good the original LSD might have been when it left the factory, after 164k there's more unlimited than limited slip these days, so it'll be more of a comparison between an LSD (any LSD) and what is now effectivley an open diff.

I see miles and hours of testing ahead of me. I'll identify some windy roads sans pot-holes and cameras for testing.

If you're in the locale you could observe and keep cave!

M

 

[Flightrisk]

I know Bilstein are the 'norm' and I'm sure they're very good, but Ken Coad convinced me to consider KW Variant 3. He succeeded. They really are rather good - the thing that tipped the balance was KW's build quality, especially with regard to rust resistance. Bilsteins did have a reputation for rust. Take a look at http://www.kw-suspension.co.uk/

I had new rubber engine mounts fitted a couple of years ago. I guess they were the 'standard' ones. How do the RS mounts differ (performance and cost)?

I am basing my choices on Richard's (Jackal) experiences with his 993; www.jackals-forge.com
Possibly he has tried them all at some point.

The RS mounts cost virtually the same as standard ones so seemed a no brainer choice. I believe they are a solid rubber unit, a bit stiffer than the C4's hydraulic filled which is in turn a bit stiffer than the C2's softer rubber. I think.

Am also looking forward to your write up once the Wavetrac is in, can a TBD really behave like an LSD? It could be the best of both worlds.

 

[matthewb]

I'll have a look at Jackal's page.

My Wavetrac arrived this morning.

 

[matthewb]

And another

 

[colt]

Hi , did your indie by any chance take any pictures of the insides of your worn lsd and what exactly was incorrect about the replacement vane set from porsche,Was it a ZF lsd or the later GKN version? Also how did your indie determine the wear on the friction plates as there is no specification from porsche?? only a torque figure for the diff to slip when out of the box and on a bench??

Christian............

 

[matthewb]

Hi Christian

No pics I'm afraid. However, I did keep the old lsd and I daresay I could dismantle it and take some for you if you'd like.

My indie's a man of few words - no salesy bs. He says that what was incorrect about the replacement vanes was that "they didn't fit". He said something was a bit odd about this part when he ordered it - it wasn't 'tied' to the G64/20 gearbox - Porsche agreed and said they'd take it back if it didn't fit - which it didn't.

No idea if it's ZF or GKN. I took the attached photo which I hope will give you some clue.

He used the torque reading to determine that the lsd was knackered. Also the car's done 165k.

While replacing the knackered lsd, he noticed the clutch was also knackered. Oh goody. The original clutch did 90k. The second clutch did 75k. Not bad I guess.

Took my baby for a 100 mile test run and I had some 'interesting incidents' which I'll relate later. Fun.

Thanks
M

 

[Flightrisk]

How has the fitted Wavetrac been performing Matthew? Any noticeable difference to the feel?

 

[matthewb]

Hi James

I'm still getting used to the LSD but on roads I know well I definitely feel able to accelerate earlier coming out of a bend and I definitely feel more confident when throwing her around (not that confidence was exactly lacking before). Maybe this is just a placebo effect but I don't think so. The LSD behaves well when suddenly coming off the go-button, and there's no discernible whine that others have mentioned with TBDs. I'll continue to do research - a tough job but someone's go to do it.