Help..................My car has a vibration in the rear that starts slow and gets bad around 60 mph, kinda afraid to go any faster. The rear gears were changed out for a numerically lower set before I got the car. This weekend I changed the tailshaft seal, pinion seal and rear wheel bearings. The rear u-joint is new and the front u-joint looks original but seems fine. I used a new pinion nut tightened until I got 20 inch/pounds drag on the pinion gear, the old nut wasn't very tight. The vibration was in the car before I did this work and it hasn't changed. It does not change if I shift from OD to third so I'm ruling out anything transmission forward. There is no odd noises from anything in the back. There was noise before with the bad bearings but it's gone.
If the gears were not set up correctly when they were changed would there be some sort of noise coming from rear and could they cause a vibration as described? Could this possibly something as simple as the drive shaft was put on 180 degrees wrong? I put the shaft back on the way it came off. I would really love to rule out the rear end and just concentrate on the drive shaft. Any thoughts or help would be much appreciated.

 

you say the car came with the vibration, so try and rotate the driveshaft 180 degrees.. and about this front U-joint, has it ever been changed?? is there any free-play in it?? it must be solid or i would definitely replace it.. i dont know about you but i replace both u-joints at the same time.. always.. just extra insurance.. not that it would break or anything.. *knock on wood* but first things first, rotate the driveshaft and see what happens..

 

I don't see how rotating the driveshaft is going to do anything it shouldn't matter which way you put it on. I wouldn't doubt it's your driveshaft that's the problem but your probably better off bringing it to a driveline shop.

 

OK so I'm going to flip the driveshaft to see if that helps, but what about some comments on the rear gears. I'd never had a differential apart until I changed the wheel bearing. If the gears were not set properly by the previous guy or if I screwed up in setting the preload will the rear end be making some weird noises or will it just quietly self destruct?