i have a slight vibration on my 99 automatic, it is rpm related, hold it in park at 2500 rpm and the slight vibration starts i see the back of the passenger seat start to shake and then it stops and 30 seconds later it starts again same symptom at 70 mph im thinking torque converter i disconnected the converter from the tube and no vibration which to me indicates drive shaft and couplings are ok

 

I am very curious on how this was accomplished.^^

 

put car on stands, open the inspection cover on rear of torque tube ,remove 3 torque converter nuts push converter back into trans so it clears the flex plate and start the engine transmission operation is disabled only torque tube inners and engine operate thats how i found my vibration

 

Mine is definitely speed related, not RPM. I can put the trans in N at 75 MPH with zero change in vibes though the engine, driveshaft, torque converter are all spinning at idle speed. Passenger side rear wheel has a twang to it, I planned on changing them anyway to an 18-19 combo.

 

Are C5 driveshafts not connected directly to the rear end?
EDIT: No, they are not. The transmission sits right in front of the rear end. The torque tube is between the engine and the transmission.

 

Absolutely!!! If the rear wheels are spinning, the torque tube/driveshaft is also spinning. Even an A4 will have components spinning. I think the car needs to go up on a lift, and have a good driveline mechanic investigate further. This problem could have many sources.....

 

So cdee, I think your test is only severing the direct(ish) connection between then engine and the torque tube. At 70 mph when you shift to neutral you have probably eliminated the engine as the source of the vibration and likely at least part of the transmission but I think the output shaft, torque tube, differential, and all the wheels and tires are still turning at 70.

 

If talking manual, yes. With the clutch mounted to the engine then yes, the d/shaft within the torque tube is mechanically attached to the wheels at the pressure plate. On the automatic however things change. The torque converter is the interface between the engine and drive train and it is mounted to the transmission with the d/shaft mechanically connected to the engine on one end and the torque converter on the other. Which means when the transmission is shifted into neutral the d/shaft is NOT being driven by the rear wheels but is mechanically connected to the engine which will have the d/shaft spinning at engine speed, not the speed driven by the wheels. Think about sitting at a light in D with foot on brake and wheels not moving at all. The d/shaft within the torque tube is spinning at engine rpm all the way to the torque converter, everything behind it are not moving.

 

Considering the issues I have seen on the forum about torque tube couplers and bearings, my guess would be a problem in the tt. But, that is only a guess.........

 

You're right cdee. I did not realize the transmission is at the back on the C5.

 

UPDATE! When having a tire repaired the tech showed me one of my rear wheels, passenger side, was slightly bent. Outer diameter was good however the inside bead lip had about 3/16" runout, very noticeable with the wheel on the balancing machine without a tire. I also noticed the bend corresponded with a nice hack on the bottom of the rocker, seems the PO (mom or dad) did a little curb jumping. I of course used this as an excuse to replace all the wheels and tires. Yesterday I installed 4 new wheels (Forgestar CF5's) and wrapped them in Nitto 555's and am very happy to report the vibration is totally gone, the ride at all speeds is less "harsh", it had a subtle rumble feeling at all speeds which is also gone. The bent wheel was subtle enough to escape the attention of 2 "experts" who had previously mounted tires to that wheel.

 

Glad you figured it out. Sometimes I tend to overthink things and many times the more obvious causes are the most likely.

 

^^ I like your location. I served in the AF during the early 80's.

 

I figured that was your issue fron the beginning. Glad you pegged it down and got new wheels along the way!

 

^^ I thought it might be as well, however I was still skeptical seeing two "professional automotive techs" changed tires without noticing a bent rim. Then again the first of those highly trained techs stretched a 235 tire over a 9.5" wide Corvette wheel and didn't stop to think if this was correct. I took about a 100 mile highway trip yesterday, the car is MUCH more enjoyable to ride in now.

 

Glad you figured this out. In rethinking this torque tube/driveshaft spinning situation, I also forgot the trans is at the rear. However, with that in mind, why would a manual trans be any different than an auto? If you put the trans in neutral on either trans, and turn off the engine, the driveshaft wouldn't spin inside the torque tube unless the engine is running. Or am I missing something here?

 

It is where the engine/trans disconnect is located. On a manual that location is at the back of the engine in the clutch assembly. If the clutch is engaged then yes, the d/s is turning at engine speed, the disconnect is the transmission through neutral. If the clutch is disengaged the d/s is not turning when the engine is running. Think of sitting at a light, trans in gear and clutch pedal depressed, at that point the d/s and everything else rearward of the clutch is stationary while the engine and flywheel are rotating until the clutch pedal is released which sets the d/s and everything else behind it in motion. On an auto however there is no disconnect at the engine, the d/s is mechanically connected to the engine and cannot be disengaged as a clutch can. The disconnect is within the torque convertor which is behind the d/s, when the engine is rotating the d/s is as well, always. As far as your question on a manual the d/s would be turning when the trans is in N as long as the clutch is engaged, disengage the clutch and the d/s will not turn even with the engine running. Leave the engine off, put it in gear and push the car. In that case yes, the driveshaft will turn and try to turn the engine. Disengage the clutch and d/s will turn pushing the car as it is not engaged to the flywheel. An auto does not work that way. Push an auto, engine off in gear and the car will move, the driveshaft will not as the engagement point is at the convertor and not the at the clutch.

 

Years back I had one hell of a struggle finding a location near my new home to mount and balance new tires on the Vette. My BMW, SAAB, F150, RAM, Wrangler no problem. No one wanted to touch the polished wheels on the Vette. So ended-up going to a Chevy dealership. Which they did handle with care (especially with me hovering over the tech while he did it) but the tech was a relatively green young fella, as they typically are, who only did fluid and tire swaps. None the less the slight bend in my polished wheel was fractional and hardly noticeable on the machine, and it balanced out. Still the car didn’t like it with the new rubber.

I didn’t go more than a week before replacing the wheels. I couldn’t stand that vibration. It made me insane. Especially because I replaced low milage but aged out NT555’s that rode true for the last 8 years. Including the day I brought it in for the swap to 555 R2’s.

Glad to hear you are also riding true again!!!

 

I thought new rubber would do it, I’ve owned mine since 2006 yep vibration.

 

^^ New rubber didn't stop mine either. Vibrated when I got the car, replaced all four tires with Conti Extreme Contact DWS06 tires, brand new and balanced. Still vibrated. Had to have one of those tires repaired, tech removed it, patched it from inside and rebalanced it, still vibrated. When I picked up a nail in the passenger rear sidewall I had to have the tire replaced. It was then the tech showed me my rim without a tire installed on the balancing machine with a slight bend on the inside bead lip. Put the new tire on, balanced it and yep, still vibrated. I installed four new rims and tires last Friday, car is now smooth as butter, it was obvious the rim, not the rubber was the culprit. Looks like you're still running stock wheels. Have them checked for straightness, you may be surprised they are not as straight as you may think, I know I was surprised to see my wheel was bent. Especially seeing 2 "techs" mounted tires to it and failed to see it also.