Hey folks,

As of last Thursday, I'm a new owner of a Lapis 996 TT. Love the way the car drives - it doesn't stop blowing my mind every minute.

Except. This :

https://skydrive.live.com/redir.aspx...!iyaBVxDoac%24

At the 3 second mark, you can hear me blip the throttle to get from 6th to 4th. The engine is barely audible. I then accelerate a little bit and then at the 7 second mark I shift to neutral. Then at the 14 second mark, I blip the throttle while in neutral. The wheel-speed-dependent drone is very very obvious in this video.

I bought the car in Dallas from RAC Performance and am on a road trip back to Seattle where I live. I'm currently in Albuquerque and don't think I should be driving the car anymore. Needless to say, I'm a bit stranded.

Any thoughts on what could be the culprit and what I should do here? I don't think it's wheel bearings - the noise does not really change appreciably if I turn one direction or the other. A friend in ABQ and I put the car up on stands and did a quick look-around. The wheels are tight. And if you rotate the front wheels be hand, there does seem to be noise coming from the center line of the car. Bad diff maybe?

All ideas welcome at this point. Please help me get home with the new car safely!

 

hard to tell,but front diff issues are not uncommon esp. w/ mismatched tire sizes.One option is to remove the front driveshaft,turn off the pasm & see if that helps-its the cheap rwd mod some have done

 

What manufacturer tires do you have and how long have you had them?

 

Post info about the tires...sizes, make/model, wear conditions...

This didn't come up during the test drive???

 

Just got a confirmation from the local dealership - it is the front diff. Not quite the diff, but more like the center shaft. This is based on just listening to where the noise is coming from with the car in the air.

Tires are RE050s on 19" 997 Turbo wheels. Tires are 235/35zr19 up front and 305/30zr19 at the back. They are reasonably new. I believe 6/32nds remaining on all. A visual examination reveals no unusual wear patterns

This is the first time I went ahead and made a purchase without getting a test drive in. I trusted the shop that was selling it and a PPI from the local Porsche dealership - both which gave the car a very clean slate in addition to the clean Carfax and low miles. I am obviously paying for that decision now... won't 2nd guess my gut the next time around.

Anyways, if it is indeed the front diff, where would I begin to search for a used one? Flea-bay shows no results. I've found the thread where the diff was rebuilt - but might prefer to put an intact one in there if possible for not crazy money.

All help appreciated guys.

 

The rolling diameters of those tires are 26.3 versus 25.5, but they should be the same!...those tires are mismatched and those sizes are unacceptable. Looking at the revs per mile, the front spins at 817 and the fronts turn at 788. So each mile the diff is trying to absorb and dissipate 30 revs. On the proper 996TT sizes this number is **3** (822/819)...those tires are putting 10 times the stress on the diff as the proper sizes.

The shop AND the Porsche dealer should make this right. How a P dealer can inspect and approve a car with the wrong size tires (safety defect) is amazing.

 

On another board a new owner of a used Turbo found out his car's noise was due to a bad cardan shaft, one of the CV bearings (I think the one at the front of the shaft) was the cause.

The reason was given that the shaft was too straight -- working from memory here but I think I have the gist of it accurate -- and this caused the bearing to prematurely fail due lack of any movement.

I sort of doubt this as an explanation but can't be 100% sure the explanation is wrong.

Anyhow, if the explanation above is something that can happen then it could be the cause of the failure *if* the failure proves to be the shaft and its bearing and not a bearing in the fluid coupling or even in the front diff.

Also, someone worked the math and believes the tire diameter mismatch played a role. I can't arque with that. Anytime one goes outside the envelop regarding in this case tire sizes on a car with essentially full time all wheel drive too great a difference in front/rear tire diameters can bring with it problems.

Sincerely,

Macster.

 

the cheap way is just to remove the center shaft, thereby bypassing the front diff...you can do it in 10 minutes...you need to take off all the covers below the tranny pull out the shaft

 

Post in the Parts for sell/wanted section. Plenty of guys with RWD and diffs sitting in their garage I would imagine! And like the others said, get new tires and see if the PPI people will help you out.

 

Here's one for $1200 used:
https://www.6speedonline.com/forums/...ferential.html

 

I just got a set of these wheels with the same size tires (stock sizes for 997 tt) Unfortunately I did not do the right research before I got them. I guess the only choice I have is to put the 315 tires in the rear. Is that too wide? The tires on the wheels right now are Michelin and they are almost new. Too bad. I think I'm going to sell them for wat I got on them.

 

Sorry to hear doc...saw this and was quite annoyed.


A

 

Thanks guys for responding to my questions. I'm currently en route back to Seattle. Sleeping in SLC for the night. Decided to take the chance and drive it back home instead of shipping it. I'll go through all the suggestions and probably put the car up on stands and do some deeper diagnosis to find the true source of the noise. I'll keep you all posted.

 

So I did remove the cardan shaft from the car. No difference. But this makes sense because the front diff is still going to be rotating when driving.

 

Oh. After removing the cardan shaft, with the front up in the air, the growling noise seemed to be a lot more audible when turning the left wheel. I never understood that, but I began to suspect the wheel bearing again.

Anyways, I took the wheel off and was beginning to start disconnecting the axle when the noise (once again) seemed to be coming from the diff. And sure enough, the left output seal is drenched. I think I'm going to have to rebuild the diff :-/