Vibration in low RPM pull

[18WheelsRollin]

Hello everyone. I just joined this forum and I'm looking for some advice. I just got a 1989 Blazer (everything stock/tbi 350). I'm trying to diagnose a vibration. Taking off from a stop everything is pretty smooth. The engine idles smooth with no smoke, rattles or vibration. The transmission (stock 700r4 I believe) shifts smoothly through each gear until it hits overdrive. As soon as it shifts into OD there is a pretty severe vibration in a low-RPM pull. Once you get up to a higher speed and RPM it smooths out again. Any thoughts? Thanks in advance.

 

[thearborbarber]

U joints in the driveshaft could be a cause, especially if it's around the 55mph speed range in OD give or take.

 

[Bent77]

Yeah I would give those a good look over. Easy enough to check and simple enough to change

 

[K85 Octane]

Try leaving it in 3rd and testing at the same speeds