mwood388

Hi Guys,

My car is a 2001 turbo with just over 110k miles, has a 1 bar tune and suspension but otherwise stock. I've been chasing a problem for a while now and I just can't figure it out. I've read every forum post that I could find that has had similar symptoms and I think I've tried or checked everything that I've read about - worn out flywheel, engine mounts, transmission mount, etc.

So the symptoms are basically a clunking sound anytime I apply or lift off of the throttle. It is particularly loud at lower rpms with little throttle input. For example, in 2nd gear at 2000 rpms if I barely apply throttle *clunk* and come off of the throttle *clunk*. I hear it no matter what gear I'm in. If I am continuously applying throttle, there is no sound. If I coast in neutral and hit some bumps or try to brake in an oscillating pattern, I don't hear any sounds. I am convinced that it is something in the drivetrain.

The two main things I thought it could be were a worn out dual mass flywheel or a worn out transmission mount. My car has the GT2 solid clutch disk and the stock dual mass flywheel. I put a new disk and flywheel in and there has been no change. Tonight I took out the transmission mount and inspected it, and it looks completely fine.

I also had the transmission rebuilt by Brian Copans (who is awesome) at BMC&GEE last month due to some bearing noise. He replaced 2 bearings but otherwise said that he could not find anything wrong with the transmission and that it actually looked really good. So I would think that rules out the transmission. It's possible the sound is just backlash between the gears in the transmission, but I think it has gradually worsened over time. If it is backlash I don't see how it would be getting worse when the gears were just inspected and had no wear and no other car I've driven had significant play in the gears like this. Short plug for Brian - he an expert on Porsche transmissions, he was very communicative, explained everything he was seeing and doing, and saved me a lot of money compared to other shops.

Other things I have checked:

• Driveshaft has a bit of play at the u-joint where it goes into the cast housing (behind the diff). The support there at the u-joint looks fine.
• Front diff supports look fine.
• The guibo flex part between the transmission and driveshaft looks fine.
• Engine mounts were were replaced about 6 months ago with semi-solids.
• Front diff fluid was recently changed, no metal bits.

I'd really appreciate any other ideas of what I could look at next. I'll answer any questions and have some pictures I can share as well.

32krazy!

wheel bearings

s65e90

Mine clunks but that's due to driveline lash w/ solid mounts everywhere.

Carlo_Carrera

Are you sure the guibo looks fine? Remove it and be sure, it is the most likely cause .

s65e90

You said semi solid engine mounts. If you also have the trans mount, I'd say it's just backlash.

32krazy!

i have all of those a wavetrac and dss stage 5 axles. rwd conversion zero clunks at all

s65e90

You have to drive it first lol. But seriously, changing all the mounts to semi-solid is what made the difference. Zero before, now on/off throttle lightly when cruising you can feel the lash that was no doubt isolated by using rubber mounts prior. The RWD also removes 50% of the driveline.

Carlo_Carrera

One other thing to check is the front and rear diff oil levels.

mwood388

Thanks for all the suggestions. I checked the wheel bearings, no play or anything. Oil levels should be good since I replaced the fluid recently and haven't seen any sign of leaking.

I went through everything downstream of the transmission just now and the thing I found making the most noise is that u-joint on the driveshaft. Does anyone know if the bearings in the u-joint can be replaced fairly easily and what that might involve? I will probably remove it from the car tomorrow just to further check the guibo and play around with the u-joint some more.

When I twist the driveshaft I can definitely hear a bit of backlash in the transmission. I didn't think it could be that loud but maybe you guys are right since I have the semi solid mounts. I think I'll look into the u-joint further and see if anything can be done there. Hopefully I'll see some change in the noise. If not, I guess it's most likely just backlash.

"02996ttx50

i also run wevo semi's, rwd w/ wavetrac. never a sound.

i'd suspect the t-mount. when worn, they will "clunk" but mostly on lateral stress movement. depends on how "worn" i suppose.

wheel bearings is also a prime suspect but they go fast from "audible" to "shot". that's a terrible pull over immediately "sound".

mwood388

The trans mount is what I went to replace earlier this week. I was pretty confident that was the problem. But when I got it off the car it looks like it's in great condition, I couldn't get the inserts to move at all and there are no cracks/tears in the rubber.

"02996ttx50

if the combo of a copans re-built box ( bearings ) and all obvious wear parts are replaced? it's a head scratcher. lots of experience with the few in this thread. all i got

GL with it, whatever it ends up being.

Kevin

Two things to consider for troubleshooting is to remove the front driveshaft and run in 2wd mode for testing.

I would also replace your tranny mount with a 997TT updated mount.

Inspection of your 4 CV joints would also be next.

After that it's a call to Brian..

ghostofpain

Hi,

i had this noise too. Changed one driveshaft. Didnt do anything. Now my gearbox got totally rebuild and the sound is completely gone.
Guess its the gearbox. The gearbox-guy replaced alot of parts inside the gearbox, even though my gearbox was completely intact and fine.
Stuff wears out...thats the proverbial wearing of time.
PS: my gearbox had 120.000 miles on it, with a couple of trackdays.

s65e90

IMO I think 2wd helps as you're missing 1/2 the driveline.