Iron City

there something that vibrates my truck to the point where I'm bouncing up and down in my seat right around 38-39mph. It starts around 37mph and stops by 40. It occurs if I'm driving on flat ground in 4th and I'm not accelerating hard through that speed, just crusing. It will also slightly vibrate in 5th while going down hill at the above speed. It will not vibrate much at that speed if I'm going uphill, accelerating hard through it, or going downhill. If I have it in neutral when going downhill it won't vibrate either. Would this be my driveshaft u-joints? Any other tests I can do to figure it out?

coalburner400

My guess would be a U-joint

jaconst

try the midship or carrier bEARing in your drive shaft too.

kd460

Rotate the tires to see if it changes anything. Just to make sure it is not a tire, and it don't cost anything to do.

I had somehing like that on a RV once, would of swore I was losing a driveshaft. Stopped and checked out driveline, everything was seemed OK. A few miles down the road a tire blew.

Iron City

Thanks guys, I'm pretty sure it's not the tires since I had the vibration before I got new tires on a month ago, and had it after the new tires. Is there a way I can manually check the U-joint or bearings?

robert chilton

Chock the tires and put the truck in neutral with the ebrake off. Now yank on it in every direction. Also try turning the driveshaft in either direction. If you see slop in any direction, other than gear lash in axle or play in the pinion bearing, then you definatly have a bad joint. It is also possible for the joint to be solid but the grease to go bad causing the needle bearings to not role. You can get a vibration that way also.