Flywheel balance
Thread Starter
Drifting
Joined: Jun 2005
Posts: 1,950
Likes: 498
From: Chino Hills CA
Flywheel balance
I got a question. My '55 has has a vibration at about 4000 rpm. At first, I thought it was the driveshaft, it felt a little like a worn u-joint, but stepping on the clutch at speed made the vibration go away. Now I suspect the flywheel being out of balance. (Now this motor I bought complete from a wrecked Chevy, which I rebuilt. It was origianlly hooked to a TH350 and I replaced the flexplate with a swapmeet flywheel, since I was installing a T-5).
I was pulling the trans anyway to fix a bad syncro, so I pulled the flywheel off. I took the flywheel down to my local machine shop to get it surfaced and balanced. They told me the could not balance it unless I brought them the crank, pistons, rods, etc and they would balance the whole assembly. This seemed odd to me. My question is, was my original motor balanced with weights welded to the flexplate, or is the majority of the balance handled by the external damper pulley up front, (something I've always assumed).
I was pulling the trans anyway to fix a bad syncro, so I pulled the flywheel off. I took the flywheel down to my local machine shop to get it surfaced and balanced. They told me the could not balance it unless I brought them the crank, pistons, rods, etc and they would balance the whole assembly. This seemed odd to me. My question is, was my original motor balanced with weights welded to the flexplate, or is the majority of the balance handled by the external damper pulley up front, (something I've always assumed).
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
The individual clutch components are balanced during manufacture (at least, in the US) just as is done with the flywheels. If you build a high RPM engine, it is probably a good idea to get the rotating parts balanced together....but you sure don't have to disassemble your engine to change the flywheel.
Since the vibration goes away when you apply the clutch, you may want to drop the clutch inspection cover and see if all the pressure plate bolts are tight. You can also put your car in neutral...leave the clutch engaged and rev the engine to 4000 rpm to see if the vibration is there or not. It should be there, if the flywheel is not balanced properly. The only functional difference is that your tranny is not in gear...everything else is the same as if you were running down the road at 4000 rpm. If you do NOT feel the vibration when doing this test, your vibration is farther back in the drivetrain. [Since the vibration goes away when you depress the clutch (at speed), it also can't be the tires/wheels.] Also, check the rubber in your harmonic balancer; if it is old and the rubber is hard and/or damaged, it may not be doing its job.
Since the vibration goes away when you apply the clutch, you may want to drop the clutch inspection cover and see if all the pressure plate bolts are tight. You can also put your car in neutral...leave the clutch engaged and rev the engine to 4000 rpm to see if the vibration is there or not. It should be there, if the flywheel is not balanced properly. The only functional difference is that your tranny is not in gear...everything else is the same as if you were running down the road at 4000 rpm. If you do NOT feel the vibration when doing this test, your vibration is farther back in the drivetrain. [Since the vibration goes away when you depress the clutch (at speed), it also can't be the tires/wheels.] Also, check the rubber in your harmonic balancer; if it is old and the rubber is hard and/or damaged, it may not be doing its job.
Thread Starter
Drifting
Joined: Jun 2005
Posts: 1,950
Likes: 498
From: Chino Hills CA
Thanks for the reply. I went ahead and took my flywheel and pressure plate to work and mounted it on a wheel balancer. The balance was off over 1 ounce. So I got out my trusty dewalt drill and some bits and drilled some 3/8" holes on the heavy end until I got it to zero out on the high accuracy setting. I'll put it back in the car on Sun and see what happens.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Not a bad approach. If it were me, I would have done the flywheel by itself, first...as I suspect that it would be pretty well balanced; my guess is that you drilled the flywheel to compensate for pressure plate/clutch un-balance. Either way, what you did should fix your problem. Just remember to mark the orientation of clutch components [for proper reassembly], should you ever need to take the clutch appart in the future. One ounce of un-balance is a BUNCH on a flywheel/clutch set. I hope that fixes your problem.
Thread Starter
Drifting
Joined: Jun 2005
Posts: 1,950
Likes: 498
From: Chino Hills CA
Problem fixed! I did index the pressure plate and flywheel so that it would stay in the same position. Put the car all back together this morning and the vibration is gone. No more powershifting into third from now on though.
