Funky driveline noise. CV?

Troubleshooting a funky noise in the MR2 V6. Hoping this could be a CV joint issue, but I'm not sure. The noise is a thunk..thunk..thunk, which is proportional to wheelspeed and I can feel in the chassis...like something binding up. The tricky part is that it only does it under one condition -- when engaging the clutch in a situation where coming off the pedal is going to bring engine speed up (downshifting without rev-matching.)

Say you're going along a 50mph. Clutch in, let the revs fall to near idle, select third, clutch out....thunks until the engine/transmission speed syncs.

I almost always revmatch my downshifts or brake until I nearly stop and shift to neutral, so I haven't noticed it until I didn't do those things.

No abnormal noise under constant cruise, tight turns, light or hard acceleration, or engine braking.

Anyone had a CV joint fail in a similar way? These are FWD-style axles. Should I be looking at something else?

Didn't someone have a problem like this recently that strangely turned out to be the clutch? May be worth checking.

Is the issue with the engine/trans speeds or road speed? From what your describing, it sounds more like a clutch than a CV issue.
If it was a CV alignment issue, I'd think you could make it worse by getting on the throttle hard. That would tweak the powertrain mounts, thus changing the angle of the shaft.

Engine mount?

Front motor mount is beaten, but not broken. I put a prybar to the engine to bounce it around and didn't get any thunks. I may replace with poly inserts, or hammer a wooden stake into the void in the front mount for troubleshooting.

Help me understand how the clutch could fail in a way that would do this. I hate the thought of pulling the transmission. It's an Exedy stage 1 clutch/pressure plate with a Fidanza FW, and ARP hardware. All new with 2k miles and everything was torqued to spec with Loctite.

DrBoost wrote: Is the issue with the engine/trans speeds or road speed? From what your describing, it sounds more like a clutch than a CV issue. If it was a CV alignment issue, I'd think you could make it worse by getting on the throttle hard. That would tweak the powertrain mounts, thus changing the angle of the shaft.

Wheelspeed / trans speed. Frequency corresponds to wheel speed, but transmission speed differential (engine slower than trans) is the only thing that brings it on.

Tyler H wrote:

DrBoost wrote: Is the issue with the engine/trans speeds or road speed? From what your describing, it sounds more like a clutch than a CV issue. If it was a CV alignment issue, I'd think you could make it worse by getting on the throttle hard. That would tweak the powertrain mounts, thus changing the angle of the shaft.

but transmission speed differential (engine slower than trans) is the only thing that brings it on.

That's what makes me thing clutch stuff. But with that said, it's hard to diagnose a noise, even harder when you've not heard it. I'd isolate that engine mount like you said for the troubleshooting aspect of it.

Cleaned up the CV joint. Worn, but I'm not sure it is bad enough to cause issues. I can catch a nail on those worn spots. No marks on the Ben Wa balls.

Not debating the clutch, but I need to understand the failure mode before I pull the tranny. If it engages smoothly and upshifts smoothly and doesn't slip or chatter, what else can go wrong?

I would definatly look at the bad transmount next... besides, if it is beat, it needs to be fixed anyway

Ordered fore/aft poly inserts. I'm going to get the axles rebuilt.

Tyler H wrote: Ordered fore/aft poly inserts. I'm going to get the axles rebuilt.

Just FYI, poly inserts on a shot mount won't help a whole lot (if they are the style I am thinking of).

Engine braking seems to load motor mounts more than any other driving action, from my experience, so you are probably on the right path.

These are the full rubber replacement, not the kind that fill the voids in the stock rubber.

http://twosrus.com/catalog/product_info.php?products_id=215

Any opinions the condition of that CV? Rebuild, or repack and reboot?

If it was a cv I'd think it would complain all the time and not just during a gearchange. I can't think of a gearrbox issue that would do thie eitther but I'd drain a little gearlube and check for metalflake or chunks just in case. Same thing with mounts. ..they should be complaining whenever you get on it or brake hard unless they aren't totally broken and make noise only on rough shifts or something. Throwout bearing? I dunno. Those cv's don't look damaged enough to make noise to me and they usually click 'steada thunk.... though that might not apply to nonsteering cv's. Does it get worse if you do your shift in a tight corner?

Update on this. Never found the smoking gun. Had the axles rebuilt and installed the poly mounts, and everything is happy. Only complaint now is the poly mounts at idle sound like a bass drop in the cabin. They aren't any noisier the rest of the time, but stop lights suck. The mount bracket holes on these cars are slightly elongated, so I'll go back and make sure they are cinched in the middle.