I have a 4.6 01 F150 with 3.08 rear end I got back in Sept. In Nov. I replaced the timing chain/guides and brakes/rotors all the way around. I have also flushed the cooling sys. and replaced all the coil packs/plugs in Nov. About 2 months ago I started feeling a vibration(feels like the truck is bouncing most of the time not bad but I know something isnt right) at ~37MPH. Not always bad but 98% of the time you can feel it. I feel it at other speeds sometimes also. 2% of the time I dont feel anything. It had older tires and I got a new set ~ 3 weeks ago and its the same. A couple days ago I put a GoPro under it and filmed the driveshaft and it does seem to be bent some. Any ideas what might be my issue or things I can check myself? One other note is the previous owner did use the truck to haul a horse trailer some and I know now that rear end was not the best for that! Truck has 210K on it and engine was replaced at ~ 150K


I went down the street and back and only got up to ~35MPH

 

I would crawl under their and see if there is any play in the pinion bearings that you an detect by hand. If not, the the rear ujoint is suspect. Wish I had one of those cameras-saves some guess work.

 

here is a view of the front end towards the engine.

 

I had a vibration that was not tires, no excess noise, no loose bolts........ dropped driveshaft and found rear U-joint was dry and "starting" to fail.

 

Im going to drop the DS soon and see what I get.

 

dropping the DS is really the best way to diagnose bad u-joints

 

Ok early morning ? I pulled my driveshaft and Ujoints look good I'll probaly change them anyway but on to the ? I live near a hill I can tow the truck up and coast down to see if there is any vibration with the driveshaft removed. Would I hurt anything? Im thinking not but Ill ask anyway. one other ? the spline shaft coming out the back of the transmission has some side to side play is that normal? Im thinking when the driveshaft extension is in place that holds it steady.
Im wanting to run the engine when I do this so I have power steering and brakes and all.

 

Running without the shaft installed you will probably loose some transmission fluid.

 

not my video but mine does this. Is it normal?

 

Even if I leave it in Park the whole time?