Vibration after open track with FFR

[mj_duell]

Originally Posted by RICK LAKE

mj-duell Mike you either broke the disc or the springs in the disc are worn out or the pilot bushing is worn out or out of round. Either way replace the pilot bushing or bearing and replace the clutch assembly. Have the flywheel resurfaced. Before you put the trans back in the car Make sure that the bellhousing is centered to the motor block. If not this will cause the same problem again. Racing is not much harder on the car than street driving unless you miss shifts and ride the clutch. You may want to go to a Kelvar clutch if you are going to keep part time racing. This clutch will take the heat better than a stock one. You will need to break the clutch in with heat cycles. They say to but about 750 miles on them before racing. I would check the dampener bolt and balancer just because. The problem is in the clutch though. Good luck on repair. If you have aproblem you can call in the evening after 8:00est. 732-254-3536 Rick L.

Hi Rick,
I'm hoping to do a tranny removal on Saturday. I've done a few before on other Cobra's so it won't be too bad. The bellhousing is a stock unit and has alignment dowels I believe. I was going to change over to a Lakewood unit, but I hate doing the alignment. I will replace the pilot bushing and I may even go with a light weight flywheel seeing that everything will be apart. I newer, better clutch will go in as well. Getting the car up in the air high enough and getting the tranny out are really my biggest problem; I'm out of space in the garage. I'll give you a call when I can. Thanks for your help.




autoxmike,
The problem happens across the rpm range without the driveshaft having to rotate at the same rpm or at all. I did give the driveshaft a good going over, even checked the pinion angle. The vibration is forward the tranny so my guess, like others, is that I have a problem somewhere in the bellhousing.

Thanks,

Mike

--Mike

[Rick Parker]

It is in the clutch disc. One of the springs in the clutch disc hub may have popped out, or as David stated a piece if the facing has removed itself. The symtoms indicate that if the disc stops the vibtation disapears. The flywheel and pressure plate are turning whether the clutch is engaged ot not.

[carmine]

What vibrational symptoms would you have if a welded on weight used to ballance the pressure plate let go. Carmine.

[RICK LAKE]

Carmine This is a rare thing. They weld the wieghts and balance the pressure plate to .000. If awieght came off on a pressure plate, depending on was dampener you are running in the front of the motor, you may get no vibration, Alot depends on the weight that is lost. 1-2 oz's you will feel at rpms over 2000. .25 you may not feel until 6,000 rpm. Are you having a vibration in the drivetrain? They have a machine for GM called EVA. It measures the vibration on the car and try and isolate it. If you have the time, pull the trans and clutch and run the motor, see if the vibrationis gone. IF gone, it either the clutch assembly or possible worn out bearing on the trans input shaft. Is it possible that the bell housing was not centered on the block of the motor. If you are running an aftermarket bell housing this needs to be done before installing a new clutch assembly and other parts. Try the trans and clutch first and run the motor. This will point you in the right direction. Rick L. If you have a question call me in the evening 732-254-3536 est.

[carmine]

Hi Rick; the vibration is felt very slightly on my steering wheel and in my seat , coming in at 2100 and diminishing at 2300 rpms. when driving or standing still reving in neutral.

[JCoop]

Motor mounts cracked or broken...just a thought...

[RICK LAKE]

Carmine What dampener is on the motor? Stock, ATI, Any markings? I will still go with the clutch assembly. Pulling the trans and clutch itself would be the first place to try and locate the vibration. It could be a bad bearing in the water pump, pulley not spinning true on the crank, If this problem just started I would stay with the clutch and flywheel first. Rick L.

[JCoop]

The reason I thought motor mounts is because for the longest time, my SPF BB would break the RH sidepipe mounts and vibrate at around that same RPM; whether driving in gear or in neutral at rest. The 3rd time I welded the mounts, I decided to change the motor mounts to poly (from Dennis O.) and haven't had a problem since. Didn't even realize it but the original rubber mounts were cracked from "spirited" revving and driving.

Worth a check, anyway. Cheers and good luck!

[carmine]

Interesting what you mention about the mounts, had that same problem with the right side, then changed to poly mounts from Olthoffs but vibration still there. What do you mean by you ( welded the mounts ). regards Carmine

[JCoop]

Originally Posted by carmine

Interesting what you mention about the mounts, had that same problem with the right side, then changed to poly mounts from Olthoffs but vibration still there. What do you mean by you ( welded the mounts ). regards Carmine

I welded the broken piece on the sidepipe mount, then I bent a cut piece of .5" round steel rod to the same angle as the sidepipe mount, then welded that to the underside of the mount to reinforce it. Ground it down to finish it and painted it hi temp black. Make sure you use a welding blanket to protect the door and sill paint...

Actually, the new mounts transmit more of the engine resonance now than it did before. It's throughout the entire range, however. I feel it more on the seatback and can get annoying on a long drive. It got rid of a drone I had between 2400 and 3500, though. I suspect that was the broken motor mount. I guess it's a trade off for the crispier feel and seemingly more immediate response I get.