About 4 months ago I had all my u joints replaced in drive shaft. Now I have a vibration in my truck from 90km and up but only when on the gas pedal. The drive shaft has play where it connects to rear diff. The smaller shaft that slides into the bigger shaft. (Not sure of proper name is) but I can slightly turn bigger portion of the rear shaft maybe 1/8 of an inch, side to side will the smaller shaft that connects to rear diff does not move at all. Is this normal? And if not how do I fix this vibration. I can find any manual drive shafts in Ontario and I’m starting to get scared. Also how much play should be in a transmission mount. I can upload my picture or video. But any help would be great! Thanks I’m advance.

 

Did you have the driveshaft checked for runout and balanced afterwards, what type of ujoints, and did they rebuild the cardan joint, I've heard its hard to get good quality parts for the cardan joint. The slip joint can wear out, but i would try greasing it until it looks like it moving slightly, pull that zerk, let a little pressure off, and drive it and repeat to insure you have enough grease on that slip joint, you don't want to fill it with grease to the point it acts as a hydraulic jack but you want the grease to work in further than where the zerk is. Make sure all 5 zerks are in alignment ( the ball socket zerk will be slightly offset), grease them every oil change, there should be a weight tacked to the shaft aswell, they can fall off if rusted. Another option is to add a gear clamp to the shaft to see if alleviates the vibes, you want the weight to be opposite of the zerks, but this may take a few tries or clamps.

FSM: https://www.ether3al.com/runner96-02fsm/propellar.html

Next option Tom Woods driveshaft, or any decent custom driveshaft shop.

 

Did the vibration show up immediately after the work?

either a bad install or you driveshaft is out of phase.