Question for you guys:

If an AWD 993 had a bent driveshaft, and this were the cause of a vibrating shifter, wouldn't the shifter vibrate based on speed of the vehicle (since the faster one goes, the faster the driveshaft spins)?

Mine vibrates based solely on engine rpm and will do it in all 6 gears independent of speed. I'm just trying to eliminate a few items as the cause...

 

I'm sure you have looked closely at the dual mass flywheel, that was the cause of 90% of the complaints similar to yours back in the day.

Another item to look at is motor/transmission mounts.
Also do a visual inspection of the motor brace/mount, they do crack.

Then there where those that complained of normal vibrations. Have you driven other 993's?

I would also plug a system tester in and see the values of each bank assuming its a 96-

It's not just at idle, but all the way up in RPM?

I think if you had a bent shaft, the car would feel like it was going to fly apart at speed. You can always check by removing them, but I feel that's very unlikely. It would be based on speed rather then RPM.

The beautiful thing about OBD2 is that you can see how both banks are running.
possibly an injector?

If you can reproduce this vibration with the car still and clutch disengaged, it's in the motor.

What's the history of the motor? Pistons and rods are matched by weight. Though I have never experienced the extent of vibration (if any) that a mismatch would cause. I understand it to be more of a bearing life approach.

 

good thoughts by Calvin

I'd add that you can disconnect the front drive shaft to eliminate if from the equation.
There is a connecting collar that can be removed.
See #2 in the diagram below

loosen both bolts, slide it onto the front drive shaft and tighten

The drive shaft is pretty tough and I'd bet it isn't your problem. But the front mount may be... doing the above may help in diagnosing but if the mount is soft or torn, the torque tube is still attached to the trans, of course

 

Mark, I will try sliding the collar up on the driveshaft. Can the driveshaft free hang indefinitely? I know that FD motorsports makes a mount for this but it runs in the 400ish range, if I remember correctly. Also, do you mean front trans mount by "front mount" or something in the front diff?

Calvin: thanks for the input. I plan on replacing the presumed original motor mounts with RS mounts and maybe doing the trans mounts at the same time. My dual mass flywheel has already been converted to an RS clutch and LWFW--luckily no stalling problems since I didn't have the work done and don't know if the EMS was reprogrammed or not. If I told you it seemed to be much worse under heavy throttle application, would that guide you towards any specific area?

(I have driven 2 other 96/97 993s without this problem, have also done the SSK and goldenrod with FULL bushing/spacer replacement at that time and have also tried numerous "additives" under the All/C shift **** to try to minimize this.)

thanks!!! Brian

 

Yes, the drive shaft has it's own bearings
No problem disconnecting it from trans

The mount we make is for 2wd conversion and not needed in your case

Yes, was referring to the front diff mount

 

I would check out the sifter and make sure it's moving on the drive shaft ok. You are suppose to have grease on the drive shaft were the shifter slides.

On my C4, the drive shaft started to make noise. I found out the rubber boot under the shifter was falling apart, and all the rubber bits were around the shifter. I blew it all out, slapped on some new grease and boot. The noise is gone.

With the center console and rubber boot off you can see the shifter, you can move it through it's movement and see/feel if it is getting caught up on anything. You can also see if there is any scoring on the drive shaft.