Hi guys,

I picked up a crazy deal on a non-starter 2003 955 TT that was immobilised with the notorious 'Steering Faulty' code. Fixed that relatively quickly and am left with a running Turbo but with a few niggles. Fixed a lot already and am left with a rough engine (replacing plugs and boost leak hunt next week). But overall it drives and pulls ok.

One of the more serious issues is a very prominent rumble and whine in the drivetrain.

Symptoms:
The car has an ever present whine and feel of resistance and grind. When accelerating it is less audible but becomes VERY prominent when decelerating. Big rumble/whine and a solid feel of resistance on the wheels.
I rattled and checked the drive shaft at the bearing and it felt ok, also the connector disk is old but has no play. Since there is that strong resistance when coming off the throttle, I was thinking front diff bearings? Wheel bearings may sound similar but it really feels like it's really slowing the car down as soon as I lift after a pull, so something more weighty must be gone (hence thinking front diff).

Any ideas on how i can narrow down the culprit before replacing the full diff and figuring out that it's something else? Any other ideas what it may be?

Any help appreciated.
Matt

 

Reading your description, front diff was my first thought as well. I've had this problem but it never got to the point of rumbling, which I think would be indicative of pretty serious bearing wear. Mine was more of a speed and load dependent whine. It's alarming that you can actually feel the car decelerate due to whatever is going on. Have you felt for play in the front drive axles where they enter the differential?

Wheel bearings should be easy to eliminate using the old left/right turn method. Transfer case is another possibility.

I don't have any good recommendations on how to pinpoint the problem further other then instrumenting the car with microphones or putting the car on a lift and running the car in drive at low speed. Since the problem is so pronounced, the latter method may actually work.

 

Might check your engine mounts too- torque strut, the rear transmission one. harder to check the cradle mounts but all could cause a rumble too.

 

I'm thinking transfer case. Change the oil in the transfer case a d both differentials.

Also, are the front and rear tires the same size or at least the same circumference if different sizes? They need to be within about 3% of each other.

 

Thanks Brett, good idea with the lift, will see if i can get the TT up there and listen out carefully with wheels spinning. Transfer case also a possibility! Thanks for the input!

 

Thanks! Checked those, a bit worn but still ok and it's likely not that due to the grindy whiny noise that goes with the rumble. Diff or Transfer case seems most likely.

 

Thanks! Yeah, Tyres all the same (275/45/20s) but I think you're right that transfer case could be an option too. I think between that and diff we will find the culprit. Does anyone know the parts overlap on both parts between the 955 Turbo and the Touaregs? Did all models have the same diff and transfer case or just some? Asking because I recently found a Touarg at the scrap yard in good condition, just had rear damage, may be a good donor.

Thanks guys, appreciate the help.

 

Just to close this one out - it was the front diff. Naturally Porsche deems it non-serviceable and doesn’t provide rebuild parts, wanting to charge a sweet 5000 USD. Picked a low mileage pre-owned one up for 450 USD from a private seller and happy ever since.


Thanks for all the comments and help.

 

How bad was the swap? Kudos on the great deal!

 

I would agree on the first post front differential. We currently have a 2006 in the shop with the same problem

 

it’s definitely a shop for intermediary skills and equipment, not a one man on Saturday job. Technically it’s not too hard, but you have to drop the subframe at least partially, which means you have to have a lift and some contraption to push the engine up or hold in place while you drop/lower it. And you def need another person to help you put the 30kg diff in place.
All in all I would say if you’re not squeamish you and a friend can do it in a well equipped workshop in about 5hrs. I reckon a good workshop can do it in 3-4hrs. Good YouTube videos available too.

hope that helps.

 

i reckon it’s mostly neglect as the diff should have no issues at all. But once/if it develops a leak and isn’t picked up it’s very quick to wear out the conical bearings and then it’s toast.