I own a 69 Ford F250 that i restored as well as lowered 4 inches in the back and 2 inches in the front. I figured that with the front being dropped as well as the rear that the pinion angle would not change that much. Not too long after i finished putting the truck back together, i snapped a Ujoint due to axle hop. I put a new driveshaft and Ujoint in the truck after it broke and ever since then, there has been a vibration when i drive it down the road. Not too long later, I broke another Ujoint again and then replaced it as well as putting traction bars on it to prevent spring wrap and axle hop. I do not think that the yoke is bent but am not sure. Does anyone know the best way to check the pinion angle? I have also been told that Ujoints spin in an oval pattern rather than perfectly round and that when you have two Ujoints on a drive shaft, the oval rotations cancel each other out making for a smooth ride. I dont know if maybe the other Ujoint could have been damaged when the other one broke. It seems to look fine though. If anyone has any info on why there would be a vibration when i drive the truck, it would be very helpful. Also i would like to check the pinion angle but i dont know the best way to go about this. Thanks

 

Yes, as a U-joint spins it speeds up and slows down for each revolution. The other U-joint does the same thing so when they are phased correctly they cancel each other out. Could it be the shafts are out of phase?

 

Just wondering if that driveshaft was actually new. Sometimes they need to be balanced at a driveline shop.

 

The driveshaft was not new but i put the truck up on blocks and put the truck in gear and got it up to about 30mph and looked underneath at the driveshaft and it seemed to be perfectly straight.

 

It doesn't take a whole lot of imbalance or being bent a little to get the vibration. Also, you can develop vibrations at different speeds. If you've changed the u-joints, I would take it to a shop to check for a bent tube or being out of balance.

 

Hey, maybe it's your carrier bearing causing all the trouble, see:

https://www.ford-trucks.com/forums/s...d.php?t=274174

 

Check my Club FTE website links section under the spinning wrench for driveline information links.

 

When you lowered the truck you changed the pinion angle. Even though you lowered the front as well as the back, that has nothing to do with evening anything out. You have to by shims that go between the rear-eng and the springs to fix the angle difference. the angle of the output shaft on the transmission, or in this case the u-joint knuckle after the center support on the driveshaft, has to be the SAME as the angle of the input shaft on the rear-end. As bb pointed out, it need to be phased correctly as well. I had the same problem on my 94 f350. I lifted it, front and back, and that changed to pinion angle. I had to figure out what size shims I needed, they look like little ramps. Once I put them in, they twisted the rear-end to the correct angle. After that there was no more vibration. Go to any good 4x4 shop, and they will know exactly what you need and tell you how to figure out what degree you need.