Vibration after open track with FFR

mj_duell · #1 (**permalink**) 10-22-2007, 09:22 AM

Hi Guys,
I have a problem I am trying to get nailed down on an FFR I recently acquired. The car is a Mark II with a three link rear and the build quality is excellent. The engine is a supercharged 5.0 and the tranny is a T-5. Last week I took the car to an open track event at Watkins Glen. It ran great all day with the exception of a leaky radiator cap, which I replaced. I ran the car fairly hard and found it handled very well and I was able to get a lot of speed out of it. Here is the problem. I was on my last run of the day on the third lap when I started to experience a very heavy vibration, which follows with rpm, from the front of the car. This vibration would go away when I pressed the clutch pedal and disengaged the clutch. It would come back immediately when the clutch was engaged. I could not figure out what the issue is. The car starts, idles and response smoothly when parked and in neutral or with the clutch disengaged. However, the vibration sets in when moving in gear and turning rpm’s above 1900. I have checked the usual suspects, driveshaft bolts, engine mount, tranny mount, header bolts, wheel lugs. It could be the clutch, but I am not getting any slip or engagement problems. Any ideas or questions that would help me figure this out would be great.

Thanks,

Mike

Ron61 · #2 (**permalink**) 10-22-2007, 10:43 AM

Mike,

If your clutch has any balance weights on it you could have lost one of them. I kind of doubt it from your description as about the only thing different when you engage the clutch is the disk makes contact with the flywheel. If y9u have an inspection plate, try taking it off and looking up in there to see if you can see anything.

Ron

wrench87 · #3 (**permalink**) 10-22-2007, 11:34 AM

do you remenmber if you used new or old driveshaft bolts?, i have heard of a lot of people find loose driveshaft bolts when they were used , the new ones have lock tite on them. also check the the crankshaft bolt at the balancer.

mj_duell · #4 (**permalink**) 10-22-2007, 11:48 AM

Quote:

Originally Posted by wrench87

do you remenmber if you used new or old driveshaft bolts?, i have heard of a lot of people find loose driveshaft bolts when they were used , the new ones have lock tite on them. also check the the crankshaft bolt at the balancer.

I checked the driveshaft bolts and everything is tight. I never thought about the crankshaft bolt, better check it. Would that cause a vibration if the bolt was loose? Isn't the balancer key'd?

--Mike

wrench87 · #5 (**permalink**) 10-22-2007, 01:04 PM

there was a post on ffr forum the crank bolt broke and actually broke the balancer?, also check the bellhosing to see if it is hitting the down tubes on either side of it and check the trans mount to make sure the tranny is not hitting the frame. just some ideas

mj_duell · #6 (**permalink**) 10-22-2007, 01:07 PM

Quote:

Originally Posted by wrench87

there was a post on ffr forum the crank bolt broke and actually broke the balancer?, also check the bellhosing to see if it is hitting the down tubes on either side of it and check the trans mount to make sure the tranny is not hitting the frame. just some ideas

Will do. That's the thing about vibrations, hard to track down. I'm just hoping nothing has to come apart.

--Mike

Roscoe · #7 (**permalink**) 10-22-2007, 01:09 PM

Could you have simply thrown a weight off one of your front wheels???

Rosoce

mj_duell · #8 (**permalink**) 10-22-2007, 01:16 PM

Quote:

Originally Posted by Roscoe

Could you have simply thrown a weight off one of your front wheels???

Rosoce

Hi Roscoe,
I thought of that, but I assumed the vibration would be still there even with the clutch disengaged. The vibration stops with the clutch pedal down.

--Mike

CobraEd · #9 (**permalink**) 10-22-2007, 01:25 PM

I would check the ring on the harmonic dampner behind the front pully just to be sure. If it is loose, it will cause very bad vibrations that change with the RPM.

.

mj_duell · #10 (**permalink**) 10-22-2007, 01:31 PM

Quote:

Originally Posted by CobraEd

I would check the ring on the harmonic dampner behind the front pully just to be sure. If it is loose, it will cause very bad vibrations that change with the RPM.
.

I'll check that out as well. I was wondering.... I beat the car up pretty good all day, what are the odds the clutch cable may need adjustment or repair? Could it be hanging up the clutch slightly and causing chatter? I didn't think of this before because I do not see any slip when I'm on the gas.

--Mike

DAVID GAGNARD · #11 (**permalink**) 10-22-2007, 03:35 PM

Mike;

If the vibration stops when the clutch pedal is depressed and the clutch is dis-engaged from the pressure plate, I would have to think it is the clutch itself, or the pressure plate........outside chance it could be a problem with the flywheel.....

I would pull the trans and check this out before running the car much more.vibrations don't usually go away on their own and can and do lead to other problems down the line....if the vibration is severe enough, it will eventually cause other things to work their way lose and cause more problems...

also, check out the pilot bearing in the end of the crank while you have things apart.....

My guess, is the clutch disc itself may have lost some of it's material and throwing things out of balance, just my hunch.....

David

Rick Parker · #12 (**permalink**) 10-23-2007, 02:08 PM

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 · #13 (**permalink**) 10-23-2007, 02:48 PM

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

RICK LAKE · #14 (**permalink**) 10-24-2007, 08:34 AM

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 · #15 (**permalink**) 10-24-2007, 10:35 AM

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.