I just bought a used 2004 Porsche Cayenne today with 84,000 miles on it. It seems like the transfer case or the differential keeps locking up and then unlocking. It makes a thumping sound in the front end but goes away when I hit the brakes. The sound will persist for about 5 minutes then the light will come on saying Lock over loaded and the sound will go away. What do I do? I had the PPI done at RUF in dallas earlier today. This occurs mostly between 65-75mph.

 

It's a full-time 4wd. What you should do is have it evaluated before driving it again. If it is "locking up..." you could end up with a huge problem. Otherwise, it could be the Cardan Shaft if it is thumping while accelerating. That is an easy replacement by your dealer or a moderate fPIA if you DIY. Either way, I would check with your PPI inspection location to see if they inspected it or just passed it through for your payment. The Cardan Shaft would have been an easy spot.

 

It thumps only at highway speeds when at neutral throttle. Goes away under acceleration and under braking.

 

I had a buddy of mine at the local porsche dealer look at it. He says it's due to the PO putting 2 different brands of tires on it. Does this sound legit?

 

Not to me. Unless they are mis-matched sizes. If they are, you shouldn't be driving it anyway.

 

Just put on 4 brand new Pirelli p-zeros. Issue is completely resolved. The 2 different brand of tires were off enough that they were engaging the transfer case.

 

That's great. Hopefully there isn't any accelerated wear to the transfer case.

 

I hope the same. I will be doing a service on the tcase and diffs tomorrow. I want fresh fluid in there to decrease any further wear. Has anyone used redline products in their CTT?

 

There are many discussions on this with several cars, my thought is and take it or leave it its up to you but I always run factory fluid when it comes to transmission and Diffs. These fluids are used by the factory for a reason, not to take away from redline which is a great product as well but with certain vehicles they sometimes tend to be finikey with types of fluids. It could be slightly thinner or thicker not what the part is used to. Remember manufactures such as porsche spends millions on research and design and the optimnum fluids to use. Of course there are errors like say the coolant pipe issue where it sounds like they went the cheap route. But I beleive the fluids they use are top notch

An example of this would be my Subaru STI not a high end vehicle but I changed out the rear diff fluid and put MOTUL. Motul is a great brand used with race teams but....my rear diff light came on after running it, spoke to a friend who has a lot of knowledge on the subject as said that the subaru doesnt like it and to go back to the factory fluid. I drained it changed it back to factory fluid Bam light went off all is well. Just my two cents

 

Exactly. There just isn't any reason to change what works. There are many fluids made for many cars. But, Porsche is a marque that has always tested and approved everything that needs to be changed and doesn't leave any room for improvement. Your car, your choice.