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C4 front diff whine

Mark Elder

PCGB Member
Member
I don't normally drive at a constant 130kph but the long drive down to Le Mans and back was tightly regulated by the threats of the Gendarmerie so I was hardly ever above of below that speed.

I've noticed quite a loud whine that I think is coming from the front of the car at this speed (well, actually at any speed, but slower it is quieter so not very noticeable and faster it gets drowned out by wind and engine noise).

Front dif oil was changed recently - so I'm wondering if the new oil has brought on the noise. It is road speed related (i.e. does not matter which gear I'm in, the whine frequency relates to road speed)

Any comments or other ideas what the cause might be. If not I'll get the oil changed again (to a different brand) and see what happens.
 
I once had a speed related whine which was diagnosed as wheel bearings. I checked carefully before getting the bearing changed and it all seemed very smooth so I decided against changing bearings and changed the part worn tyres instead-I think they were Avons that were on it when I purchased car. This immediately cured the whine and it never returned. Worth considering/ruling out.
 
Your story sound's very familiar, a few years ago my front differential needed replacing with a reconditioned unit, my car too was making a whine which got louder with an increase in speed. Bob Watson engineering who carried out the work, said at some point in its life the front diff leaked diff oil and cooked itself. The seal's may have been replaced by a previous owner but damage may have been done over a period of time, the rest was wear and tear. I'm not saying this needs to be done in your case, but it sounds familiar.
Was the diff in good order when oil was changed?
 
HI, you could try this, jack up the car on axel stands and run the car up, listen to the diff with a long screwdriver against the diff housing, you will be amazed at what you hear if a part has gone bad. It also removes any suspension and tyre noise, just be careful . Horse
 

ORIGINAL: MoC2S

Pirelli PZs are also known to whine when the tread gets low ..

HTH, cheers, Maurice

I agree, I'd eliminate the tyres as a source before moving on to the more expensive suspects. Can you borrow another set of front wheels or perhaps your mechanic can do this for a short test?

pp
 

Mark,

The fact that you've not been aware of the whine before your trip would appear to mitigate against it being tyre-related and more likely to be due to a wheel bearing or the diff.

I must say that, from extensive experience in vehicle NVH/refinement, gear whine is a very strange phenomenon in that sometimes the ear does not detect it but once it does, it's impossible to ignore! It could be that it's been present - and getting progressively louder - for some time but you haven't been aware of it until your period of extended constant speed running during your Le Mans trip.

Without the use of a microphone or accelerometer, a wheel tachometer and spectrum analyser it would be difficult to pinpoint the diff as the definitive source of your whine. I really wouldn't recommend horse's approach - sounds much too dangerous. As a first step I'd certainly check the wheel bearings for excessive wear and, as you've indicated, use a different gear oil to see if that helps.

Hope you get the problem resolved.

Jeff
 

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