993 C4 diff sounds

[BrianM]

I have a 97 993 C4. Over the last couple of months i have noticed a grinding noise coming from my diff but only when i'm in wet conditions etc. I assume the torque converter only kicks in then. At first a local specialist and the OPC thought it was likely to be the engine mounts which were in turn putting a strain on the diff which i was feeling thru the pedals and steering. However they have now been checked and they are fine. This worries me as my OPC wants to whip the engine out and carry out any repairs they see fit. Worse case scenario is scary, best case scenario is £2k for the labour to remove the engine give a report and refit the engine. This is something i cant live with and i would doubt my warranty would either. Have any of you guys heard of anything similar. My local specialists are phenominal to say the least, they service more Porsche's than the OPC does, nearly all of them club members. So my confidence in them is very high as they have worked wonders on previuos cars for me, i'm just looking to point them in the right direction if i can. Thanks for any input you have.

Brian

[domster]

Errr, I don't see how whipping out a 911 engine and refitting can cost 2k... most techs whip the engine out to change the plugs at the 24k service interval as it is so easy. Are your techs asking for 250 quid an hour or something?

[BrianM]

They are quiet an arogent bunch and the assumption is that the customer know sweet FA and also has too much money. They estimate they will have to get the engine out, strip down the diff, create a report and assuming it needs nothing done re-fit the engine and charge me an estimated £2k in the process. The specialist I use are far more practical and honest i have to say. I'm just looking to help point them in the right direction so i'm not paying for labour time that may not be necessary.

[BrianM]

come on guys has no one got any ideas what this sound could be coming from my diff ?

[david hype]

Brian, one thing that I learned via a recent post, is that the forum is excellent to get general opinion.

The problem is that it is almost impossible to diagnose specific problems on-line.

I would suggest that you try and contact any fellow C4 owners on PH (as you are doing) and try that other lot in the USA and see if they have experienced any similar problems! Try and get someone with genuine 993 experience to ride in the car with you...

[BrianM]

Thanks I'll do that.

[roygarth]

Also try www.Rennlist.com

[JohnM993c4]

Which diff are you referring to? Noisy rear diff is mentioned in a Porsche TSB, remedy is replacing worn LSD plates - but the rear diff just pops out the side of the gearbox, there is no need to drop the engine, it is only a couple of hours labour. The viscous coupling might be a bit trickier to get at, maybe that needs the engine dropped?

[BrianM]

the noise is coming from the front of the car, its a C4, thats my worry, if it was a C2 i would be less bothered as the effort to access the diff is a lot less.

[JohnM993c4]

The C4 has the same rear diff as the Carrera (albeit the LSD version, which was an option for the Carrera). The front diff (aka front axle final drive) can be removed and replaced without going near the engine. The centre diff/viscous coupling lives in the front end of the gearbox, getting to that does require dropping the engine. The centre diff is behind where you sit in the car, so if the noises are definitely coming from the front it would seem more likely that the problem lies with the front axle final drive or driveshafts (or even the power steering, stranger things have happened). There have been some reports of viscous coupling failures on Rennlist, if that happens the gearbox oil would most likely be contaminated with the silicone fluid from the coupling, draining the gearbox oil might reveal that. There is in a fairly simple test for correct function of the centre diff, but it does require a 4-wheel chassis dyno, even simpler is lifting the car, put the gearbox in neutral and see if both front wheels turn when you turn one rear wheel and both rear wheels turn when you turn one front wheel.

If it were me, I would let a good independent look at the car if it is not under a Porsche warranty. If it is under warranty, get the Service Manager at the OPC to have the discussion with the warranty people up front to see where you would stand.

[BrianM]

Thanks john, its been puzzling lots of people including the OPC and the specialist as it is only apparent during damp conditions where the torque converter kicks in.