cstreit

Gang,

I've had this rear end "clunk" when starting off in 1st and 2nd gear for a month now in the 96 993. I assumed it was the CV and decided to tackle it once the weather here went south.

So I got under the car yesterday and did some exploration. I can't find any play in the axle, though it really sounds to be coming from the right rear of the car.

It manifests itself when I start from a stop and/or let the clutch out in 2nd. I jacked up one side of the car and can move one of the rear wheels back and forth about 1.5-2" measured at the tire.

It almost sounds as if the pinion gear had way to much play with the ring gear. I'm assuming the car has an open differential as I get no "slippage" in the diff once the wheel moves that 1.5". You can hear a bit of gear lash if you rock the tire back and forth.

I talked to another 96 993 owner who said there were a number of these that some component issues from the factory on the late 95 builds. Wrong shaft installed in the trans because of mismatched parts. His was replaced by a dealer on Porsche's tab. Suppose it could also be overly loose bearings in the siff case...

I'm VERY hesitant to take the car to a dealer as I don't want to get raped, but if this is the issue, I don't see what other option I have. The car has only 50,000 miles on it so I can't figure out how this could possibly be failing....

Any ideas?

ca993twin

I wish I had a better memory... on so many levels... but on this issue... it seems that this has been discussed before, and it turned out to be something simple... like loose rear sway bar drop links or something like that. You may need to jack the car with both rear wheels off the ground to ensure that the sway bar isn't loaded. Then poke arounds at suspension components that simply need to be tightened up. I hope that's all it is. Please post back with your results.

cstreit

I did a fair amount of inspection of the rear suspension mounting points... I also noodled on this for a while and am thinking that the "planetary gears" inside the diff houseing are loose rather than this being an issue with the ring/pinion gears because there is none of the typical whine or noise associated with bad pinion depth...

Pete Debusmann

I think it could be a bad dual mass flywheel. Not sure though.

Pete

cstreit

Interesting. I considered that, but with the amount of rotational free-play (2") Its making me suspicious of the diff...

TheOtherEric

Isn't it possible that rotational free play could also be caused by a bad DMF? Seems like a plausible symptom to me.

viperbob

The rotational free play has nothing to do with the DMF. It is the interface with the diff(through the splined axles) and the pinion shaft. I have seen a diff literally EXPLODE recently. The dead giveawy there was a problem was when I changed the gear oil, and there was a tink, tink, tink sound going into the metal drain bucket. The planetary gears were the ones that disintegrated. Ring and pinion were fine. These are some cheap diffs these days.

Martin S.

Just be done with the damn noise and take the car to a top flight Porsche technician. I am certain there are lots of these folks in the greater chicago area. Anyway, that's what I would do!!!

cstreit

Thanks guys. I am a Porsche mechanic ( www.moto-delta.com )... Bulk of the work I do is early racecars though, so the nuances of the 993 are outside of my experience. I'm pretty certain now that it's the planetary gears inside the diff. I've never seen an early open diff do this though.. Good excuse for an LSD anyway.

Porscheologist

Funny but this sounds just like the "clunk" I had for about two weeks. Turned out my clunk was a loose AC compressor. All the square nuts had fallen off!! The giveaway was my AC quit because the belt came off. I thought it had broken so I bought all new belts (they needed to be replaced anyway) and when I went to loosen the AC compressor it was already loose!! Be sure not only to check under the car but in the engine compartment too! Good luck!

chris walrod

At a minimum, drain the gbx oil and have a looks for chunks. Could be your spider gears starting to pit and break apart...

cstreit

Is failure of the open style diff's common? This car has only 50k miles on it! Make sme wonder if the P.O. ran it dry at some point, there is a "coating" on the engine bottom that looks like burned fluid...

chris walrod

Most likely Cosmoline is what you are referring to. Golden brown color? Soft and waxy texture?

I wouldnt say 'common' per se, but definitely not unheard of. As these cars age, I am sure what was a rare failure before, may become more commonplace.

I will still prefer the air cooled cars

cstreit

Chris,

Thanks. I also considered that it was cosmoline because it has that color, but it was crispy and flakey... However this could just be from years of baking on the engine.

Clearly I'm going to have to check the gear oil and check that for "bits". I'm hoping that I can drop the diff out without removing the engine and tranny...

Greg Fishman

Did you take the axle off the car? I had one that was making lots of noise and the cage that holds the bearings were broken. Lots cheaper to fix than a LSD.