C4 Front diff whine

I was hoping to delve into the collective knowledge base here. I was driving a 996 C4, similar to my own, today, and couldn't help notice that there was a faint whine from the front end. I mentioned it to the owner and she said that her garage had told her that it definitely was the diff and not wheel bearings. However, it wasn't worth bothering with as 1. it is very faint and 2. would be super expensive to rectify. It got me thinking, as I have never heard of anyone else with a similar issue, why would the garage say that it would be unreasonably expensive a job to consider? Is there some complexity that any competent gearbox rebuild specialist would struggle with? Certainly it is an area of these cars that I had never considered to be a dangerously expensive component fail, if it were to occur. Does anyone have any experience in this domain?

I had a similar noise that was indeed diagnosed to the front diff. A new diff is £4k+ and so on their advice, I opted to have it rebuilt by Northway; I couldn't tell you exactly what they did, but it was a bit over a grand to have it done, almost all of which was labour. In any case it certainly seems to have fixed the problem. My noise started out quiet but over a year or so became pretty unbearable so I'd suggest it's probably not going to get better by itself.

Tell her to change the oil before she does anything else.

Most garages would tend to quote for a new diff i expect hence " its expensive " You can change the bearings , i've done one years ago but repair versus replace is always difficult for a garage .. We have to warranty the job is one thing and stripping apart an item only to find its not an economical repair does entail a cost .. Hence replacement is the favoured option at times . yes it can be done though .

Yep can be done - mine's been done twice! Once for input shaft carrier bearings, and once for output shaft bearings. Many years/miles apart and both times in the region of a grand. As above, new diff is wrong side of £4k and Porsche only. Plus about four or so hours to fit. Watch out for oil leaks - well known that the seals fail and I suspect that this exacerbates diff failures if you don't clock it in time. Next time I'm just going to RWD the b@stard!

I will have one for sale as my 36k miles turbo is being converted to 2wd. MC

It could also be the tyres especially if running on Pirellis. My brother had this earlier this year and feared the worst that the front diff was on it's way out. Our indy said about changing the tyres as he had heard of this before so he had a new set of Michelins fitted. Problem sorted and the ride transformed :thumbs: The pirellis were only about 5 years old but were rock hard and perishing!

Thanks for all the very useful and informative replies everybody, I knew that this was the very place to get comprehensive and sensible options :thumb: I will pass on the options and opinions and they should cheer up the owner no end :worship:

We can re-build these front differential units. https://www.instagram.com/p/CIDyB81hc31/?igshid=852gmocqo5it

There is also the option of removing the propshaft, diff and driveshafts and converting to 2WD. Some C2 front uprights would complete the job but are not strictly necessary.

Take the diff out. Speak to 9e. Excellent 'upgrade". You will need coil over suspension to be able to adjust the front height.

Hardly an 'upgrade' if you want AWD.

Mine had a faint whine when coasting and it turned out to be the support bearing at the prop shaft end of the diff. The bearing was only about 30EUR and 30mins to fit when a garage had the diff out to swap the drive shaft seals. The total, including new bearing, seals, labor was about 500EUR. I supplied new plugs and fluid, so count an extra 100 or so for those.

I've read a few threads on various forums where a front end whine has been diagnosed as the diff and it's been something else.