C4S front differential bearing

I have an '02 C4S with 40K miles on it. My front differential is making noises like noisy tires. It is uniform, and goes up and down with vehicle speed. It is not a wheel bearing, and I cannot feel it through the steering wheel. It is louder now than it was last summer. So I'm assuming there is a growing problem with the differential. Whether it be a bearing or what-have-you. If I assume the least expensive problem, does anyone have recent data or prices on replacing a bearing in one? Is this a dealer-replace-only item? I have seen some older comments on the List here about it, and was looking for some more recent information. Thanks much, Steve

Steve, the C4S making grinding noises in the front differential could be the 'viscous coupling' damaged. Have a shop check the front differential for any damage internally. I just replaced mine after a similar grinding issue. Have you had a 'smog check recently' by any chance? Especially when the noise first started?

Sam, I have not had a smog check. Plus I don't really know when the noise actually started. It isn't that loud that all of a sudden I noticed there was a noise. Did you have to replace the entire differential? Or are there replaceable parts in it? Can you tell me what the costs were? Thanks, Steve

The only reason I asked about a smog check is that's how mine was destroyed. The Technician at the Smog Station did not realize this was a C4S (incompetent to say the least) and ran the car on a 2 wheel dyno, which caused the damage. The shop that did my repair is also my personal local Porsche Indi shop and they do excellent work. The entire differential was not replaced but both front axles, the viscous coupler and some other parts were replaced. They checked for further damage elsewhere but found none. Total cost was $5K. You need to take it to a Porsche shop and have them at least find out what issues you have, then you can determine the actual budget for your repairs. You really cannot use my repair as a gauge for yourself as you don't know if the same issue is within yours. They should be at least be able to guide you on an estimate after checking.

5K is kinda scary if you think of it.....

Thanks for the details back. I'll do a little more investigating and see what I can find out. Steve

Quotes source post: 8812672

I agree but what options do you have if you drive a C4S and the viscous coupler and axles were damaged? Parts as you can imagine are frightfully expensive and coupled with labor rates. If it were done at a dealership it would probably be closer to $8K. If the differential had been damaged, then that would have required a complete new differential as I'm told Porsche does not supply parts for re-building. (That statement was from a friend who's the Service Manager for Porsche in the Bay Area.) Porsche ownership and repairs are kinda scary if you really think about it.

Quotes source post: 8812737

Good luck as you progress through this repair. Keep us posted as you find out more details. I hope it's not as bad as I mentioned for your sake.

Some time ago I came to realize that the C4 aspect of my '01 is so non-functional that should ANY part fail it will get REMOVED entirely.

Quotes source post: 8813004

Why is it non-functional? How would you remove it entirely? My questions are for information only, as I'm new to C4S ownership and your comments intrigue me.

I'm beginning to wonder if I've got an issue with my viscous coupling/front differential. Just today, my C4S began to make a noise from the front end. It's intermittent, and I've only been able to replicate it a couple of times. It only happens when I'm coasting downhill in gear. It sounds a bit like a slipping belt, but from the front of the vehicle. If it makes this noise and I give it a little gas, the noise stops entirely. So far, I've only heard it in 3rd gear or in 4th gear. Looks like a trip to my mechanic is in order. Any thoughts? Does this sound like the front differential? FWIW, I had the front differential fluid chaged at my 90,000 mile service, which was two years ago.

If your front diff goes out, you can usually find used ones on ebay for about $1000. Or, you can just remove the AWD entirely. It's as pretty much as simple as removing the drive shaft, differential and then taking the CVs apart and removing the axles (and leaving the axle stubs in the hubs). A lot of the high horsepower Turbo guys do it.

I think I'd rather leave it intact. My preference would be rebuilding it if possible, but I don't know what's involved. I'll see what my mechanic finds.

If you remove the dif/cardif from the front...wouldn't that mess up the PSM? I am beginning to see the severe limitations of the 4 wheel drive system myself....but I love the wide butt

Quotes source post: 9234428

Apparently, no. Quite a few people on the 6speedonline forums have done it with no side effects. If you do a search for "rear drive conversion" or something like that in the 996 Turbo forum you should find quite a few threads about.

Quotes source post: 9234700

I haven't searched those threads or anything but I can't help but be intrigued. I wonder if the conversion is reversible. After having my second DE last weekend I have spent several days plotting and scheming for my next move...Gear up the C4S for the track and just deal with the limitations of AWD, buy a miata or boxster track toy, trade the C4S for a Cayman S, sell the C4S and buy a 996 C2, or go in a totally different direction and trade up to a GT3... I can't believe I would even entertain the thought of pulling the front diff out of the C4S...oh god what is happening to me!!

Historically (according to the threads I've read about converting), the AWD 996 guys cosistently turn better lap times than their RWD counterparts. And yes, it is completely reversable. Takes about three hours to remove it if you know what you're doing and a few more to re-install it. The hardest part is rebuilding the outer CV joints since you have to take them apart when removing the AWD. I'm tempted to do the conversion myself, but coming from the Audi world I've grown pretty fond of AWD.

Ive considered pulling my front diff out. If the turbo guys can do it so can we. Ive tracked my 4S over 20 times since i bought it and as long as PSM is off the car is really predictable at the limit. If she gets too loose i just flatten the gas pedal and the front end will begin to claw and straighten the cars trajectory. That is really the only time i've felt the AWD system work. Plus, we can shed 70+ lbs...

Sorry hope I'm not hijacking the thread... Hardback it is encouraging to hear others sticking with the 4S on the track! Keeping my car is really my least expensive option (damage risks excluded). Ahh what a wonderful decision to have to make Now back to C4S diff repair discussion!

Op, now that this isuue has been brought up. My car was making a gear type whine after letting out the throttle at high speed, say above 60 mph. I couldnt figure out what the issue was but now im curious if it has to do with the front drivetrain. Interested to hear what your diagnosis is.

Quotes source post: 9234819

I hear you....this is my 4th AWD car. however....your Audi is a true AWD car, geared, not a viscus coupled car. I find my C4S to behave quite differently than my previous AWD cars. Technically speaking, the system on the C4S doesn't provide more than 5-10% drive unless you lose traction at the rear...so you are effectively driving a RWD car, with juuuuuust enough FWD pull to help lessen the inherent oversteer. It should make a better handling 911. That is...if your viscus coupler is function properly

Quotes source post: 9234910

Probably a long shot, but worth a mention I guess, hope. Last Dec. on a road trip back east my Turbo starting making a whining noise that sounded wheel bearing. Really started to notice it on drive south from OKC to Wichita Falls and found that if I kept the car's speed under 70mph the noise was not that bad. Hard to do since the limit was 75mph. Anyhow the noise was so distrubing, so out of car's character that I stopped in Wichita Falls for the night and the next morning after making some phone calls to various Porsche dealers turned around drove back to OKC and the Porsche dealer there. (The dealer in OKC was 130+ miles away; the nearest one in TX was over 140 miles away. Albuquerque dealership was around 500 miles away. I didn't want to head east if I could avoid it.) The senior tech took the car out and reported the noise was tire noise. The front tires were cupping/scuffing a bit on their inside edges and this was causing the noise. I felt the tire treads and sure enough I could feel the feathering and the slight roughness to the rubber of the tread on the inside edges of the front tires. The rear tires felt just fine. After driving away I got to thinking and remembered at a motel parking lot the 1st or 2nd night out pulling just a bit too far into a motel parking space and just nudging the front tires against the low curb. I never (well, save this one time) do this to avoid upsetting the car's alignment. I suspect this nudge knocked the front toe out a bit and this accounts for the tires' abnormal wear because in all my miles of driving my Porsches I've never had any front tire wear problems. Just a thought... run your hands over the front and rear tire tread surfaces and see if you can feel any feathering. If so the noise might be tire noise. Sincerely, Macster.

I'll check that out. Thanks...

I just found that my noisy front end was the driver's side wheel bearing. After talking to mechanics at both Porsche dealers here in St. Louis, I learned a lot about "noisy front ends". They informed me that there are plenty of C4S owners that participate in DE's, and they rarely heard of any damage caused by such driving. Secondly, I learned that if you are mechanically inclined, you could repair/remove the front differential yourself, with just a few specialty tools needed for the bearing replacement. Thirdly, not all front differential bearing failures exhibit the classic noise upon failure. Learning that, I put my car on jack stands and removed all four wheels. With the engine running and slipping it into gear, the culprit was easy to pinpoint. Even at idle in 6th gear, the driver's side front wheel bearing was very noisy... no stethoscope was needed since the other corners were essentially silent. Bear in mind all the safety precautions, it's pretty stable on the jack stands. So for less than $400, I was able to pinpoint the noise, replace the wheel bearing, and the cheesy sheet-metal clips that hold the underpan on. Thanks to all who made comments and suggestions up front when I was trying to diagnose the problem. Steve

So for less than $400, I was able to pinpoint the noise, replace the wheel bearing, and the cheesy sheet-metal clips that hold the underpan on. Thanks to all who made comments and suggestions up front when I was trying to diagnose the problem. Steve[/QUOTE] Nice man! Good to hear!!

Mine's at the mechanic now. It wasn't the tires - I had them off over the weekend for an inspection. I should have a diagnosis this afternoon or tomorrow.

Initial diagnosis is that there are two issues. The first is a bearing in the differential. The second is an issue with the pinion gear. My indy is researching this issue now to look for the parts necessary to rebuild the transfer case/differential. Porsche considers this to be a "non-servicable" unit, but this shop has rebuilt them before. I should have a few options to consider later today or tomorrow.

It looks like my mechanic was able to find some, and possibly all of the parts to rebuild the differential. They're pulling it, and opening the case to assess the damage. If the cost to rebuild it is reasonable and the parts are available, then I'll go that route. If not, I'll be putting in a used unit. There are several available with low mileage and a warranty. Just for grins, I checked for the price on a new unit at Pelican Parts. The original part (996 349 010 02) has been superceded by a new part (996 349 010 03). Pelican Parts has the new OEM part for $6,116.25 plus shipping. Woof!

I've decided to go with the rebuild option. My bearings were shot, and one was really bad. There were metal shavings in the bottom of the case, and my viscous coupling was in bad shape. Fortunately, the ring and pinion gears were in good shape. I'm having everything cleaned up and rebuilt with all three bearings being replaced and the viscous coupling being replaced. It should be as good as new when it's finished. The cost was far less than a new unit, but more than a used unit. I'm looking forward to getting the car back home.

how many miles were on your car when it started to make noise and do you track or autocross the car? Thanks,

I have not tracked the car or auto-crossed it, but I have got that in the works for this summer! The car had approximately 108,000 miles I started to hear the noise.

The rebuild should be complete this afternoon. I should finally have my car back tomorrow. I haven't seen it for such a long time, it will feel like I got a new car!

Quotes source post: 9364090

Congrats! Two questions: - what did the rebuild diff, installed, run you? - what did the noise sound like when the diff was on its way out? Cheers, FLi

I won't see the final bill until tomorrow. The quote for the differential rebuild was $3,200, which includes parts and labor. All the bearings, as well as the viscous coupling were replaced. I am also having the CV boots replaced (torn again), the brake fluid flushed and changed and the oil changed. The noise sounded a bit like the squeal of a slipping belt coming from the front of the vehicle. I noticed most when I downshifted and was decelerating, with my foot off the accelerator. I couldn't really hear it during acceleration.

Quotes source post: 9364248

Thanks. Something to keep an ear out for. Cheers, FLi

The car is finished. I picked it up yesterday afternoon after it sat at the shop for over 3 weeks waiting for parts. It feels like a new car again! It's totally quiet up front now. I realize now that there was a gear/bearing whine going on for some time before the failure. The mechanic showed me the worn bearings, and they were pretty bad. I'm really happy to have it back. I ended up having an oil change, a brake fluid flush and change, front differential rebuild, CV boot replacement and tire balancing done. The total was $4,082. Not cheap, but necessary. The car drives like a dream now...

That's quite a hit, but glad to hear the car is back on the road again. Cheers, FLi

ouch. For that much money I probably would have ended up just removing it

Where I live, I like the AWD system. I was pretty happy with it as a compromise between a used unit and a new unit. Also, even though it seems expensive, the occasional one-time hit like this is much easier to take than a regular monthly payment on a newer 911. I'd rather keep this one with no car payment for a few more years...

What did the VC cost? IF it was listed on your bill. Thanks

The part was $1,334.34.

I have a 996 c4s 2004 in need of front diff. Any for sal ?

I have one from my car that I will sell cheap. As a little background, my C4 was making a noise that I thought might be the front differential. I bought a used differential and swapped it out, and still had the same noise. Turned out it was the bearing in the transmission, which my shop sent out to have rebuilt by G-Box in Colorado. Now the car is quiet as can be. And I have an extra differential sitting in my garage. PM me if you would like to talk about it. By the way this place in CA will rebuild the front differential for $995. http://californiamotorsports.net/col...t-diff-service This does not include the viscous clutch. For the original posted, how did they know the viscous clutch need replacing?