Vibration after open track with FFR
 

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

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 :confused:

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

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

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.

:D

--Mike

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

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

Hi David,
I was afraid someone would say that. Tonight I checked the balancer, driveshaft, engine mounts and tranny mount as well as clearances. Nothing wrong. That seems to leave me with the inevitable. :( One thing I did find during my search is that I have lost a header bolt on the driver’s side and a few others were loose. I was unable to fire up the engine to see if that had any effect because of the time. I’ll give it a check tomorrow. I have sworn off any new thrashings of the car until I get the problem fixed.

:D

Thanks,

Mike

Mike;

Loose header bolts,especially on aluminum heads is very common......I've lost track of how many came out on my car......that should not have any effect,except maybe blowing a header gasket now and then....Usually after every two or three track sessions,once the car cools down,I run a wrench on all the header bolts,after two or three times doing that you should be o-k, but keep checking them......

I've seen some clutch disc's loose a piece of material before, sometimes a pretty good size chunk can come off and then it will throw things out of wack, also,if your pressure plate is the type with the weights on the "fingers", you could have lost one or more of the weights and that will definetly throw things out of balance...

I know it's a pain to pull it down, but it's better to do that then have something else vibrate loose and tear up.......

At least you did not find pieces of oil rings on your oil drain plug like I did this weekend!!!!!!!!!!!!!!

One thing I've found out is that track time on a car is about equal to 10 times that amount of mileage on the street or MORE.......I spend at least one hour checking things on the race car before hitting the track each time just to make sure everything is tight and in good working order............

David

Hi David,
Yup. I know I'm headed for a tranny removal. No big deal just time consuming. I have seen cars that have never leaked or made any noise suddenly start spraying oil and back fire when I tracked them. You are correct, the track does take it's toll.......I'd never stop doing it though :LOL: I always check things out before track time and between runs. I lost a couple lugs at WGI and was lucky enough to make it back to the garages. I had tightened them down before my first run that day. Taught me a very valuable lesson about checking the car every time!

I'll keep you up to date on the clutch. I won't have time to get to it until this coming weekend.

"At least you did not find pieces of oil rings on your oil drain plug like I did this weekend!!!!!!!!!!!!!!"

Bummer! Never a good sign. Let me know what you find.

:D

--Mike

Mike; does the vibration go away or become less as your rpms go above aprox 2400 rpm.

Mike,

Its easy to see why you may not have seen the missing header bolts! :LOL: :LOL:

http://www.cobranet.com/coppermine/a...s/IMG_0073.jpg

No, but I wish it would. :LOL: It does seem to level off a bit when the rpm's get high enough.....maybe around 3000 or so. It's really driving me nuts. I will figure it out in the end, but I believe I'm in for a long search. If I had to describe the vibration, I would say that it is not present at idle. It builds starting just slightly on throttle and is pitched with the RPM's. The engine vibration is not noticeable by eye, but is definitely coming from the engine, accessories or bellhousing area. The engine performance is normal with a steady idle, no back-fires, rough idle, stumbling etc. It almost feels like the timing is off if you know what I mean. Something is not balanced or the adjustment is off.

--Mike

I knew that pic would turn up eventually :LOL: . Maybe I need to put those glasses back on and the problem will show itself! That was a fun event, can't wait until next year!

:D

--Mike

Bad U-Joint? Sometimes when a U-Joint goes bad the driveshaft will vibrate within a certain RPM range. Above or below that range the vibration doesn't happen. This happenend to an old POS Plymouth Fury when I was in college.

Broken Disc or bad pilot bushing
 

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.