My 52 Buick was in a bad wreck last fall. Had to replace the front frame with a FatMan subframe. I have drove it about 1400 miles this summer. I have a 425 nailhead; a switch pitch turbo 400 and a rear end out of a 72 Chev ½ ton pickup. A vibration has developed. Most pronounced at 30 miles an hour under cruising or moderate acceleration. I used a used flex plate and I remember that during assembly it was not perfectly flat. Could a bent flex plate create this kind of vibration?
I would think that would show up more during starter engagement. Often constant speed vibrations are at the trans output shaft and rearward through the driveshaft/driveline, as those parts change rpm as road speed changes, while engine rpm changes throughout gear changes, so engine-related vibration would be dependent on engine RPM rather than road speed. Suspect rear trans mount, u-joint wear (especial cardan joint wear if present). If you have a "dual" driveshaft with a card joint mounted to a crossmember, that mount is suspect too. Devon
The explanation of engine RPM vibration verses drive line vibration makes good sense. I just have a simple drive shaft with a u-joint on each end. I can not feel any movement at the u-joints. I suppose I could remove the driveshaft and have it checked to see if it was bent during the wreck or the yoke that slips into the transmission.
Rear transmission mount can be checked before removing the driveshaft, might be a good place to start. Some lose adhesion between the rubber and steel components, look fine at rest but may be damaged or worn upon inspection. Even a loose connection between trans crossmember and frame should be checked now that I think of it. Good luck! Deon
I replaced the transmission mount and motor mounts after the wreck. But I will loosen the trans. mount and raise rear of trans. up and inspect everything back in in there.
I would start with the tires personally. I feel like this kind of issue is usually the rubber. Maybe swap from to back and see if it changes?
Somewhat easy check on drive shaft is to mark the rear shaft at the joint and rear pinion, remove the shaft, reinstall it after rotating it 180 degrees. If it is a phasing issue, it will correct, if not, if is is better or worse, you can leave it or put it back. But it will rule that out. I've had some where it made a very substantial change, and other times where it was negligible difference.
I removed my transmission mount, I can get some movement when I clamp one end in a vise and thread a bolt into the piece than mounts to the transmission mount. Thank you for all the ideas my work is cut out for me now.
