Driveline vibration '68 Z-28

[camaroguy62]

I have a 68 Z-28 that has a driveline vibration between about 55-70 MPH. It occurs in any gear or coasting in neutral, so I don't believe it is engine related. I had a second set of tires and wheels that I changed out on the rear and it still does it. It seems to come from the rear and is severe enough that it rattles the cardboard package shelf. There is no vibration in the steering wheel, some vibration on the shifter, and when I re-bought the car it had this condition. In detailing it, I replaced the following: Front and rear springs, all suspension bushings, body mounts, brake lines and cables, motor and transmission mounts, complete exhaust system--I can't remember if I changed out the universals, but think I did. I had the differential open for inspection-no obvious evidence of problems-replaced the seals. I did not change out the rear wheel bearings, the axles seemed tight in the bearings. I did nothing to the 4 speed close ratio (it's not a rock crusher). I am thinking it must be: driveshaft or universals, transmission output shaft, wheel bearings or axle(s), or pinion angle to transmission angle misalignment. Any help in diagnosing this condition is greatly appreciated. Note: This is a true Z-28, I bought it new, sold it and bought it back. It is mostly numbers matching. The unibody is stiff-no rust or flex.
Camaroguy62

[ct91rs]

Originally Posted by camaroguy62

I have a 68 Z-28 that has a driveline vibration between about 55-70 MPH. Camaroguy62

It only occurs during that speed range, and isn't related to a specific rpm range?

[camaroguy62]

Originally Posted by ct91rs

It only occurs during that speed range, and isn't related to a specific rpm range?

.
Yes it vibrates at that speed, independent of which gear the transmission is in, and also does it when the transmission is in neutral at that speed, coasting with the engine at idle (900rpm).

[Morley]

Try disconnecting the drive shaft at the rear U joint and turn it 180 and reconnect. See if that helps, may have been installed out of phase.

[camaroguy62]

Originally Posted by Morley

Try disconnecting the drive shaft at the rear U joint and turn it 180 and reconnect. See if that helps, may have been installed out of phase.

I will give that a try and let you know.
Thanks,

[camaroguy62]

Originally Posted by camaroguy62

I will give that a try and let you know.
Thanks,

I Turned the driveshaft 180 degrees at the differential yoke connection and that reduced the vibration by about 50%, but it was still there. I then took the driveshaft to Shaftmasters in Lincoln Park (near Detroit) and they straightened and balanced it (one day turnaround). Seems to have eliminated the vibration all together. Thanks for your help.
Camaroguy62