I guess this is the place to start. I am new here, located in Jacksonville. New vette owner. Know my way around cars but vettes are new. I started out looking for posts about good repair shops in the area but there doesn't seem to be any based on what I found. So, I thought I would just ask my question here and see what happens.
The C4 I bought has 100k miles and is in really good condition. Very few problems, mainly cosmetic stuff. The real issue is that it has this vibration that occurs mainly at the top end rpm in third gear, and then again in fourth. It seems to do it more when I hold out and don't shift to the next gear to push the engine more than normal. As the vibration starts it appears to loss a little power but yet the transmission doesn't slip (the tach doesn't race). Pushing in the clutch seems to stop the vibration but I am not sure if it is because the clutch is not engaged or I have removed throttle from the engine. Shifting to the next gear stops the vibration. Once past those points the shifting and speed are as normal.
My first thought is the clutch is the problem but it seems to be fine every place else. Also, it seems to do it more when cold.
It also has a custom exhaust and I sometimes wonder if it is the exhaust that is vibrating. I have found places where the pipes were rubbing the frame, but fixing those and it didn't really change anything. Maybe there are more places.
Well, I've never had a C4, but I guess some generic troubleshooting couldn't hurt.
Is it a vibration or a rattle that you are hearing? Does the frequency of the vibration or rattle increase and decrease with vehicle speed or engine RPM after it starts?
The loss of power comment might indicate that the engine is having ignition misfires at higher rpm. Have you tried replacing the ignition components? With 100K miles on it, unless you know the plugs and wires have been replaced recently, you might want to think about doing that.
I've also read that the OptiSpark can sometimes be a problem and cause similar problems like you are describing.
Thanks for the response. It is more of a vibration, something like a shudder or shimmy, not a rattle at all. I do feel it in the gear shift knob. It does not change once started but it does go away when the pressure is let off or shift to the next gear.
I have changed the spark plugs and wires. Even different brands of spark plugs to see if that was it. Same.
The video (thanks for that) didn't really match the symptoms, but I will check more into that possibility. Also, there are no codes generated that I can tell that would be related.
I really do lean towards some issue with the clutch assembly, and would go ahead and just replace all of it mainly because of the mileage just to see if it fixes it.
However, it appears that it is not possible to replace with the original equipment. And from what I can tell I would be replacing with inferior quality clutch parts and producing other noise issues.
Yeah, I wonder if that clutch has been replaced? Maybe an unbalanced clutch assembly?
Pushing the clutch in disconnects the engine from the entire drive train, so I wonder if keeping the revs up on the engine even while pushing the clutch pedal in has any effect on the noise?
Just seems odd that it only does it in third and fourth gear at the high RPM end, and not in first and second gear.
Also, you might want to try just taking your foot off of the throttle without pushing in the clutch when the vibration is taking place. See if the sort of engine braking effect has any effect on the vibration.
Not sure this will produce answers, but surely some evidence. I've got my own sort of drivetrain noise in my C5Z that I'm not absolutely sure what is causing it. Not the same as yours, but still, something that has me scratching my head trying to figure out what is going on BEFORE I want to tear apart anything. I'm not real keen on "exploratory surgery" on vehicles.
I have tried removing throttle and that doesn't seem to do anything to the vibration at the current speed as it slows down slightly with out pressure. Even speeding up doesn't change anything. The only thing that does change it is either shifting, or pushing in the clutch, but that's shifting and doesn't really reveal much.
Anyway, so your comment about you having your own drive train noise/vibration/unsmoothness makes me wonder if maybe this is just a mechanical personalty issue. Maybe it is just the way the car wants to run. Who am I to try and change a woman's, sorry, car's personality.
Nope. My issue is completely different. It's a drivetrain noise that takes place normally from starting off from a dead stop. Possibly the clutch, but darn if it doesn't sound like a bearing to me.
I just brought this up to let you know that drivetrain noises can sometimes be real troublesome to diagnose. Possibly the only reasonable stance to take is to just ignore the noise till something actually breaks to show you exactly that was making the noise. The alternative would be to just start replacing every possible culprit till it finally goes away, starting with the most likely, and progressing possibly to the "who the hell would have ever figured THAT was making the noise" finale. Which could get REAL frustrating and REAL expensive.
Vibration in 94 C4
Linear Mode
