My sons 94 regular cab 3500 has a drive line vibration somewhere. It feels too slow to be engine speed but faster than tire speed. He pulled the rear drive shaft today and replaced both u-joints and had it balanced at a machine shop. The front u-joint was wore a little. The vibration is now less evident at 55 and a little more evident at 60 and up. The truck has a Gear Vendor overdrive and the drive shaft has been altered but it is straight and in balance. It also has the air ride suspension on the back and I'm wondering if the drive shaft angles are wrong. I have checked the rear transmission mounts and everything is tight. Both the rear yoke and the GV yoke are tight. There is no center bearing on the regular cab so now I'm puzzled. We're going to put new tires on it next week since it has odd ball tires on it now.
Any ideas?

 

Be sure the U-joints at opposing ends of each shaft are properly indexed to each other.

Is there a bad bearing in the Gear Vendors?

 

The u-joints are indexed properly according the the shop. That is the first thing I asked them to check. The rear bearing in the GV seems to be tight also.

 

Joel, I am not sure about the cause, but on my'89 with a GearVendors, I had the same vibration, at the same speed. I changed tires, balanced and rebalanced, changed universals...ad infinitum.

Still vibrated.

good luck

 

Check your drive line working angles there should be no more than 1 degree of diffrence between the the u-joints 1/2 degree for a gas engine. The gear vendors extra length has probaly thrown the working angles out.

 

Thats exactly what I am thinking. I'm wondering if I should get some shims and shim the rear end to raise the front of the pinion slightly.
We're going to check the drive line for out of alignment this week end again. He said the tail shaft moves back and forth about a quarter inch if you rock it. Sounds like the rear mount could be a little worn.

 

Jack is right. Seems nobody checks the working angle of the pinion. I would almost promise that is the trouble. Let me know where you get the truck shims. I ordered shims from Mopar and they were the automobile type. To narrow for the truck and the pin hole to small. $ 50 wasted.

..Preston..

 

You should be able to find the shims for the rear axel at any good spring shop one that does truck repair would be a good bet! I would check your angles with a protractor or a spicer angle master first before buying the shims. you may also have to raise or lower center bearing or rear tranny mount to gain correct working angles! Good luck !