Vibration at speed

[70_F100_Custom]

Just bought a 1970 F100 Custom and the vehicle has a vibration at speeds above 40 MPH. Im thinking the culprits might be either unbalanced driveshafts, u-joints or drive shaft bearing. The pickup is powered by a 240 attached to a 3 speed tremec and has a two piece driveshaft. Any ideas?

[fmartin_gila1]

Make sure the two driveshafts are synced, examine the shafts closely to see if any balancing weights have come off, ck for any worn or loose U joints, ck for loose mountings of both the hanger bearing and the U joint mountings, ck for pinion bearing slop.

Fred

[70_F100_Custom]

If the pinion bearing is bad wouldn't the seal show signs of leaking? No signs of a Diff leak.

[fmartin_gila1]

Not necessarily, the seal will accomodate quite a bit of flopping around without leaking. Just try to move the yoke around to see if there's any slop in the pinion bearings, keep in mind that you have the main bearing right at the yoke and the pocket bearing at the other end of the pinion. When you are chasing something like this, do not dismiss any possibilities.

Fred

[70_F100_Custom]

Just checked all U-joints and pinion no movement, though I do have considerable movement in the rubber around the Drive Shaft Bearing. It looks as though the rubber bushing may just be worn and not as stiff as it probably should be. I can see cracks in the rubber. I believe this may be the culprit. I will change it out today and post a comment after a test drive.

Andy

[70_F100_Custom]

I also forgot to mention that I have no balance weight on either drive shaft. Nor does it look like there were any on them originally. Is this not what the center bearing support was for to correct any imbalance?

[70_F100_Custom]

After replacing the drive shaft bearing I checked the U-joints one more time and found that I am able to move the output shaft from the transmission. Even I know that other than rotating the output shaft should not jiggle. Sounds like a transmission rebuild to me.