Mystery Vibration

Cajunmech · 11-21-2006, 01:26 PM

I really need help with this one. I have a very disturbing vibration that seems to be generating from the engine @ 1,600 rpm again at 2,200 rpm again at 3600rpm. It feels like it is coming from the drive train but when I disengage the clutch it stops. I can produce it sitting still and slowly bringing up the rpm to thise levels. I am getting ready to do some tuning this week, I know that the car is running lean. Check my profile to see what mods I am using. The car performs perfectly. No loss in power, no smoke, good gas mileage, no overheating. Runs like a scalded dog! Checked the motor mounts and they are fine. Could it be the clutch / flywheel area? My mechanic is stumped, the dealer hasn't a clue. My car is a 98 coupe.

Please help!!!

Cajun

Mark Dalton · 11-21-2006, 04:09 PM

That's a weird one. Is it definitely coming from the eng? When I put my Hurst shifter in I picked up a vibration at certain rpm's, although it's usually higher in the power band than you describe. Possibly something related to all the work done under the car (i.e. x-pipe, headers, exhaust). If it's one of those I would think a thorough inspection would have found it. If it does it with the clutch in or out, that may rule out the tranny. I'm sure you've already checked all the connections and ducting and such for the blower. Maybe someone listening outside the car when you reproduce it can zero in on the location a bit better. Good luck.

Cajunmech · 11-21-2006, 05:58 PM

Yes, the blower was removed, replaced the pulley and idler pulley bearings and the belt. Just installed the new fuel system and the injectors tomorrow and then some tuning. Hopefully the lean condition is causing some of this. Thanks for your reply. Still searching.

exile · 11-21-2006, 08:16 PM

A minor expense and sometime a big help is to change the tranny fluid and the rearend fluid to a synthetic like Royal Purple, Redline, Amsoil, or the new Mobil synthetic fluids. Don't know that this would fix your problem, but it would eliminate the possibility clutches in the tranny and rearend needing a change or topping off and synthetics seem to help these cars. Has anybody heard anything negative about putting synthetics in a 98 model?.........Tom

Changed both transmission and differential fluids in my 02Z06 and it made a world of difference. I was experiencing no problems at the time except for the usual stiff shifting and it fixed that

...........Tom

RevXtreme 1 · 11-21-2006, 08:49 PM

If I read your post right, you say it disapears when you push the clutch in. That would lead me to believe that it is torquetube back. There are 2 carrier bearing paks in the tube that could cause the vibration, or it could be in the rear end it'self. A small chip off the ring gear could act that way.....Try coasting along while moving and see if it goes away when you depress the clutch, or maybe that is what you are already doing. Just under a load? (acceleration) or letting off? Just maintaining MPH? Make sure you check the dampner bolt before anything. Let me know, I will try to help diagnose.

Corvette Concepts · 11-21-2006, 09:18 PM

Hi Cajun,
First thoughts would be clutch assembly but if you can hear the issue sitting still it may not be clutch. It could possibly be the throw out bearing. How many miels of the car? I will do a bit of research tomorrow, but I saw a suggestion to change fluids to other synthetics such as Red Line. Be very careful with this type of fluid change. We used Red Line in our 99FRC and developed a crunching when hard shifting at the track. When we changed back to GM fluid the noise went away. Just a bit of info....I will give your issue more thought but I have to get off line now....nighty night.

Quote:

Originally Posted by Cajunmech

I really need help with this one. I have a very disturbing vibration that seems to be generating from the engine @ 1,600 rpm again at 2,200 rpm again at 3600rpm. It feels like it is coming from the drive train but when I disengage the clutch it stops. I can produce it sitting still and slowly bringing up the rpm to thise levels. I am getting ready to do some tuning this week, I know that the car is running lean. Check my profile to see what mods I am using. The car performs perfectly. No loss in power, no smoke, good gas mileage, no overheating. Runs like a scalded dog! Checked the motor mounts and they are fine. Could it be the clutch / flywheel area? My mechanic ais stumped, the dealer hasn't a clue. My car is a 98 coupe.

Please help!!!

Cajun

Cajunmech · 11-22-2006, 08:38 AM

Quote:

Originally Posted by RevXtreme 1

If I read your post right, you say it disapears when you push the clutch in. That would lead me to believe that it is torquetube back. There are 2 carrier bearing paks in the tube that could cause the vibration, or it could be in the rear end it'self. A small chip off the ring gear could act that way.....Try coasting along while moving and see if it goes away when you depress the clutch, or maybe that is what you are already doing. Just under a load? (acceleration) or letting off? Just maintaining MPH? Make sure you check the dampner bolt before anything. Let me know, I will try to help diagnose.

I guess I misrepresented the involvment concerning the clutch. What I meant to say was it doesnt matter what I do with the clutch. Engaged or not the vibration is still there. However the vibration is more dominate when load is attached. Please continue to help, all assistance is greatly appreciated.

Cajunmech · 11-22-2006, 08:45 AM

Quote:

Originally Posted by Corvette Concepts

Hi Cajun,
First thoughts would be clutch assembly but if you can hear the issue sitting still it may not be clutch. It could possibly be the throw out bearing. How many miels of the car? I will do a bit of research tomorrow, but I saw a suggestion to change fluids to other synthetics such as Red Line. Be very careful with this type of fluid change. We used Red Line in our 99FRC and developed a crunching when hard shifting at the track. When we changed back to GM fluid the noise went away. Just a bit of info....I will give your issue more thought but I have to get off line now....nighty night.

There are 57K on the clock. This vibration happens when the car is in neutral or underway. As I mentioned the vibration becomes magnified when load is applied. It is a pretty scary sound. Please help.

Mekanic · 11-22-2006, 10:20 AM

sounds like an out of balance flywheel, but it wouldn't be vibrating at specific RPM's..

Cajunmech · 11-22-2006, 10:49 AM

Quote:

Originally Posted by Mekanic

sounds like an out of balance flywheel, but it wouldn't be vibrating at specific RPM's..

The flywheel was replaced with an aluminum flywheel. This was done before I owned the car so I cannot vouch for the quality of the install, but that is as good an idea as I've heard so far.

Thanks, Ed