I have a 1997 4x4 off-road short bed, regular cab f150,5.4L, just replaced u-joints in the rear drive shaft, I have a vibration when I deccelerate from 75MPH, It's starting to become more noticable at 70 mph cruising now, I'm thinking rear end issues, previuos owner ran diff lube real low.
Appreciate any help.

 

Was vibration present before the U-joint replacement? If so, is there any type of noise present and can this vibration be changed with the use of the throttle. In other words is the vibration constant, or is it only on decel or accel?

 

when the driveshaft was re-installed, did the u-joints get lined up. are they out of phase? that'll cause vibration.

 

I think O5 Super has it. One of the things the engineers at the car companies have the most trouble with how a vehicle resonates. You have all or the mass of a rotating drive train, wheels rolling, moving over a road surface, and a whole host of other things. These engineers literally tune the vehicle like a musical instrument any thing that throws the vehicle out of tune will cause vibration.

 

i hope so Transmaster. also no chance that a weight on the shaft got knocked off or shaft is bent? not sure if there is a stub shaft from the tranny on those model years. could be bad u-joint on there also.

 

Vibration was present before u-joint replacement, new joints made no difference, it only happens on deceleration.
It used to happen only when I let off the gas at 80mph so I believe it's getting worse.

 

Good points mentioned above. Just to clarify on the U-joint alignment in case its an unknown territory to you. Two piece drive shafts are splined together at the slip joint. In modern times, one of the splines are keyed or machined so they can be assembled only one way. Look at the driveshaft, the ears is what the U-joint goes into. If the ears are placed, one up and the other down, when attaching the slip yoke we need one ear up and the other down. This is in time and the way it should be. Am still challenged by your vibration. If its possible, have the drive shaft angle measured by a qualified drive line shop, not a dealership. Dealerships are great and have trained their techs to repair the new products. Unfortunately, alot is lost as years pile up and factory new designs are altered.

 

I marked all the caps with a white paint pen, I took it in to a shop because of the CV assembly at the front and the shop put punch marks to match up the caps so I believe everthing is in phase.
I'm still thinking rear diff.
I appreciate everybody's input