Rear U-joint problem
 

My son has a 72 LWB GMC with a 350 / 350 auto. The rear joint lasts about 1000 to 1500 miles. The truck has just developed this problem. With a new u-joint in place no vibration at highway speeds. You can tell when it starts to go bad it begins to vibrate on highway. It has gone thru 3 now. The truck has not been in an accident or high centered. Any idea's?....
Thanks, Parrish

MIGHT BE DRIVESHAFT OUT OF BALANCE, HAVE A LOCAL MACHINE SHOP CHECK IT :confused:

IS TRUCK LOWERED USING BLOCKS, COULD BE THE REAR PINION ANGLE IS OFF :confused:

I'M SURE YOU WILL GET MORE OPINIONS WHEN OTHERS CHIME IN ;)

Front , middle or rear? Truck been lowered or raised?

Add another question. Single or two piece shaft?

It is the stock height for 1/2 ton, 2 piece drive shaft. I have looked at the driveshaft and does not look like any weights are missing. It is the u-joint that connects the rear end to the drive shaft.

Even with the weights there, the drive shaft can be out of balance, slightly bent etc. I would tend to take it to a "big truck spring/driveshaft" place. Take the whole driveshaft---with center bearing and have them check it out for true, balance, bearings etc. They will find any problem and get it right. They also tend to be pretty fair on prices for labor and parts too.

Another thing is that you may be over tighting the straps on u-joint. This will tend to make the cups out of round which will eat up a joint in a hurry.