I just bought a '71 Dart and it has a vibration at 30-50mph. Above 50mph it seems to level out enough that it's not so noticable. Also, if I let off the gas while it is vibrating, the vibration goes away.

The front two tires have uneven wear from not being rotated. The car probably also needs an alignment. But since the vibration stops when I let off the gas, these problems seem to be unlikely culprits. Am I wrong in thinking this?

I am thinking maybe the driveshaft is out of balance, or I have a u-joint going out. Does this seem logical? Do you all have any other suggestions for me?

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'71 Dart Swinger

Possibly something in the rear end, a pinion bearing? More load is placed on it during acceleration then coasting.

I believe your problem is the classic example of un-balanced tires. Before spending $$$$$$ check your front suspension & fix the tires . Your problem will most likely be solved.

Sounds like u-joints. You can block up the car and crawl under and check them for abnormal movement/play/slop/wear.

To check the u joints pull the drive shaft out of the car. I had a 68 Valiant and after I replace the transmission with one that had a lock up converter everytime it went into lock up I had a vibration. Anyway it turned out that the holes for the transmission yoke had become enlarged enough to let the u joint slide back and forth. 2 new u joints and a yoke and it was fixed. I used a yoke for the 904 that I had that came from a van. It worked perfect and no more vibration.

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Former bent 6 owner
Mark

Well, I changed the u-joints and all is better now.
Thanks for your help.

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'71 Dart Swinger