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Mystery Vibration

C

Cajunmech

New member
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:dancer01:
 
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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.
 
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.:thumbsup:
 
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:thumbsup: ...........Tom
 
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.:thumbsup:
 
Vibration

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.


Cajunmech said:
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:dancer01:
Click to expand...
 
RevXtreme 1 said:
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.:thumbsup:
Click to expand...

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.:yesnod:
 
Corvette Concepts said:
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.
Click to expand...

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.:thumbsup:
 
Mekanic said:
sounds like an out of balance flywheel, but it wouldn't be vibrating at specific RPM's..
Click to expand...

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:thumbsup:
 
RevXtreme 1 said:
I would tend to agree on the clutch/flywheel. Still check the dampner bolt for proper torque!!!
Click to expand...

I assume that you are speaking of the front lower pulley on the crankshaft?
Also, is there a possibility that it could be from pressurization of the crankcase from the supercharger via some hoses that are connected to the pcv valve. The reason I ask is that there are some symptoms of oil in the aftercoolers. Not much but a misting. Could there be a pressurization issue. Also the sound is like a shutter to the ear and the vibration is in the peddals and the shifter and the seat. Again I can do this with the car sitting still and in neutral or in gear.
What should the torque be?
Frustrated:crazy03: :crazy03:
 
Can't remeber the specs off hand but I think 90-110lbs. Yes it is the lowest pully. I doubt it is in any way related to the supercharger, I expect clutch/flywheel at this point if the dampner is tight.
 
RevXtreme 1 said:
Can't remeber the specs off hand but I think 90-110lbs. Yes it is the lowest pully. I doubt it is in any way related to the supercharger, I expect clutch/flywheel at this point if the dampner is tight.
Click to expand...

Well, I guess I'll get into the clutch / flywheel and check the assembly. Assuming that I find all fasteners at the proper torque, the next logical step would be to have the pressure plate and flywheel inspected. Where would I bring these devides to for such an inspection?

Thank You for your help and have a safe and Happy Thanksgiving! :peelout 1:
 
Cajunmech said:
Well, I guess I'll get into the clutch / flywheel and check the assembly. Assuming that I find all fasteners at the proper torque, the next logical step would be to have the pressure plate and flywheel inspected. Where would I bring these devides to for such an inspection?

Thank You for your help and have a safe and Happy Thanksgiving! :peelout 1:
Click to expand...

We can take care of it for you.:thumbsup:
 
this may sound off the wall, but i had a terrible vibration that was very similar to yours. clutch in or out. it would do it sitting still but was more pronounced under load. it would shake the whole car and come through the shifter. i replaced the b&b prt's with borla stingers and it went away instantly. the prts would cause a harmonic through the whoile car and would even cause the tail pipes to shake on only the right side. just one more thing the check out before pulling the trans and rear end. should you need to have the rear and trans pulled revextreme did a rear swap for me and it has been flawless. no issues with their work.
 
Thanks to all that participated in the troubleshooting process. I took the car to Rev-Extreme and the techicians inspected the car. The diagnosis was that the crankshaft pulley was wobbling and that is what was causing the vibration. Well, I spent over 700.00 to replace the pulley and the vibration was the same. I am fully aware that this can be a very difficult diagnosis however after the repair, I went to the front desk and told them that the issue was still at hand and what should I do next. I am not here to bash this shop. Yet after spending this amount of money, and not bitching them out for missing the diagnosis, I began asking for more help. I remember standing at the front counter asking a group of technicians and principals for help and recieved no response. Just a couple of guys shaking their heads saying much of nothing.

This is a horrible place to be when you need help and are desperate for it. I felt abandonded in my search for this help. Not one time was I asked if I was satisfied.

Being fully disgusted concerning this issue, I was at Advanced Performance Tires and Rims in Drew Park and began to ask if anyone could tell me what was going on? I was refered to Greg @ Anti-Venom. I called him and stated my case. Upon his inspection of my car the next day, he immediately told me that there was no way the pulley was the source of the vibration. He said the vibration was not being generated from the front of the motor but from the rear.

His diagnosis was that it was certainly being generated from the clutch region. The clutch was inspected and found to be a new ZO6 clutch with a Fidenza aluminum flywheel. What had happened is the prevoius owner either replaced the cluth himself or had this done, and standard thread bolts were used to secure the pressure plate to the flywheel. Metric threads are the required fastner. Subequently, all of the bolts had lossened and one had sheared off completely. The clutch was in great shape but the flywheel must be replaced.

I wish to thank Greg @ Anti-Venom for properly diagnosing this issue and spending the quality customer care time with me to solve this problem.

The moral here is buyer beware. Ask more questions and get several diagnostic opinions before wasting money.

P.S. I picked up the old pulley and took it to a machine shop to test the truness of the rotation and behold, it was within the tolerence of the manufacturer. Just be careful where you spend your money. This thread is meant to be a service to all Corvette owners and nothing more. :shrug01:
 
Thanks for the follow-up. Good information! Greg @ Anti-Venom seems to be "The Man". Good review :thumbsup: .............. Tom:)
 
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