I am looking for advice, considerations on what may be wrong with my car as I’m really concerned about any potential costs.
I have had a 2003 996 Turbo for about four and half months and covered about 1500 miles in it so far; the car has done less than 40,000 miles. After I had the car for about 2 and a half months I noticed a ‘droning’ from the front end so the car went back to the supplying dealer. They too noticed this and the car went in for a diff oil change and an additive as well.
The noise has steadily got worse from this point and now, at circa 80mph, there is a significant ‘drone’ from the front end. The car has been back in but the dealer cannot diagnose what the issue may be and we are getting close to the point of stalemate and whatever action that brings with it.
My worst fear is that it is the front diff and light searching has revealed varying horror stories for parts prices for this.
I have also seen mis-diagnoses stories where it has turned out only to be a wheel bearing but I would have thought that the dealer would have been able to arrive at this conclusion pretty quickly.
My questions are…is the potential of a diff being shot a real one? If this is the case, any thoughts on the likely price as I don’t really fancy getting caught with a huge bill? Any thoughts on any tests to assist the diagnosis process but, as this is a Porsche Indy, I would’ve thought they would have this dialled.
Any advice would be most welcome.
The front diff being bad is a possibility but a slim one. The diff is pretty robust and it doesn't carry a lot of torque. I mean it gets 5% unless the rear wheels spin and the fluid in the fluid coupling heats up and thickens and then under severe cases the front diff can receive up to 40% of the engine's torque.
Unless you've been using the car to practice on WRC courses...
A wheel bearing is another possibility. Since one of my Porsches has had a bad wheel bearing (the Boxster at 80K miles and that was 173K miles ago...) and I've so far not had any diffs go bad, I'd think wheel bearing before diff.
Now my 03 Turbo happens to make a noise that is while not a droning sound is a worrisome noise nonetheless from the front end, worrisome enough and out of character to the point that on a road trip a few months back had me at a dealer (after driving around 150 miles out of my way) to have the source of the noise diagnosed.
The noise was bad enough that I held the car's speed to around 70mph when legally I could have gone faster and I always (almost always) go as fast as the limits allow, especially when I have nearly 2K miles to cover and hardly any time to do it in...)
Anyhow, I suspected a wheel bearing.
Turns out it was the front end alignment. The tech found signs of the front tires cupping/feathering -- you could feel the feathering/slight roughness -- which was causing the noise.
What I had done was at the start of the trip -- 2nd day out -- being really really tired I pulled too far in to a motel parking space and both front tires nudged a low sidewalk (below the front air dam) enough to upset the alignment. I know this because I keep the car's alignment on the money and drive the car to avoid knocking its alignment out.
So, before you scrap the diff, replace the wheel bearings, give the tread faces of the front tires (and rear ones while you're in the mood), and see if you can feel any signs of tire cupping.
Might as well point out that these tires can get noisy as they age and wear and got through countless heat cycles and if one is not used to it -- and even if he is (my Boxster's tires are worn out -- new ones on order -- and the noise is quite loud and intrusive) the tire noise can have one ready to replace the wheel bearings, or rebuild the diff.
In the case of my Boxster and its bad wheel bearing, the tire noise was so bad it wasn't until after I had all 4 tires replaced the indy shop owner noticed the bearing noise during the test drive and reported same back to me. Even then it was not clear which wheel bearing was the bad one. We both drove/rode in the car and we both offered up our guesses and our guesses agreed so I had him replace the suspected bad bearing and it proved to be the bad bearing.