ca993twin

My TT has a distinct drive train howl at exactly 80 mph. Gone at 75, gone at 85. Happens in any gear. The howl is gone if there is no load on the car. It howls with any amount of load. I'm pretty sure this is coming from the front transaxle. I believe this has been going on forever, but it was very evident on my recent 2100 mile roadtrip.

My first plan is to change the fluid (also the transmission fluid) with Mobil 1, and "hope" the noise just disappears on its own. Anybody have any thoughts, ideas, suggestions, or funny stories to make me feel better?

When I bought the car, the previous owner said that he had fixed this problem, and had a receipt from LA Porsche dismantlers for a used transaxle. That was done about a year ago. Stupid me didn't know how to test for the noise, and I took his word that it was gone.

Help me Rhonda.

viperbob

Steve,

Wasn't it a used front differential, not the transaxle that was replaced??

Let me add a couple of points Steve if I may. The noise seems to be transmitted very strongly through the drivetrain tunnel. Steve does not appear to have a lower shifter boot (from an earlier short shifter install) and a good size tear in the upper rubber boot. This just makes the noise a lot more audible in the cockpit. The harmonic is strong at the speeds indicated by Steve, and does sound like it is coming from the front of the tunnel.

There was a post here recently from a guy that had a bad front diff with pictures. I can't find it by searching. Anyone remember that??

Moose

I know this sounds funny but how old are your tires? If I remember correctly, don't you run Kuhmo tires? The only reason I say this is that I had balance problems in a last car that caused noises at freeway level. I have also had tires that are load at a specific speed, like 80. Both cases, changing tires solved it all. My car has similar noises coming from the rear at 90 and changes as I change the speed or load. I figured it was the same tire problem I had on my last car as the tires are not very new.

ca993twin

Moose,

Well, I'm the guy that runs new S03s (225x40x18) in the front and new Yok Sports (295x30x18) in the rear. I'm hoping that VB is correct, and its some rubber thing that is missing. I did the short shifter about 4 months ago, but my commute doesn't get me up to 80 mph, with the stereo off and the windows closed very often. So I can't pinpoint when this howl started.
And yes, VB I meant "front diff". Thanks.

Cy

Hey Bob:

I believe the VC thread you're referring to were posted by steve_eo. There were 3 or 4 thread he posted over the past few months from figuring our how to test for a non-operational VC all the way through the install of the new part.

Hope that helps.

Steve Weiner-Rennsport Systems

Hi Steve:

Although I'd have to hear this for myself to be sure, I'd say that you might have a tire issue.

Typically, R&P noises increase with speed and bearing noises do not usually do this in one narrow speed range. I would check the oil level in the front differential and inspect the unit for any evidence of oil leakage,.....

If you possibly can, I'd suggest swapping front wheel/tires with someone else and give that a test drive to see if anything changes... its time well spent.

If that doesn't afffect the noise, then its time for a pro to check it out. Changing oils will not make that go away.

ca993twin

The reason I don't thinks its the tires is that the howl will go away if you go to a very light load or no load with the throttle. Being somewhat load dependent probably puts it into the front diff. I hope VB is right, and this is a normal noise that is simply not sufficiently dampened in my car due to a shifter boot or related problem. Or, perhaps the magical properties of Mobil 1 will cure all these ailments (and give me some extra HP? Hell, if I'm dreaming, why not?).

viperbob

Steve's,

It ain't a tire issue. Sounds like a gear related howl. Slows down under 80, but still there. Then gets a little quieter above 80 mph. With clutch in it still makes this noise. I think it is the front diff. Steve, check out the postings recently for the viscous coupling. You might want to follow the suggestions for checking yours.... While the lack of rubber makes the noise clearer Steve, sorry but you have further issues...

Steve Weiner-Rennsport Systems

Well,.......After that last tidbit of information that the described noise is related to throttle position, its likely a differential issue.

When a "howl" changes with throttle position (load) AND speed, thats either carrier bearings or the R&P.

Changing oils will not help you here.