Ok, first of all let me say this forum rocks. Have found 99% of my answers just searching. However, my latest truck 94 f150, I6, M5r2, 2wd has a odd vibration issue that only surfaces around 45, usually 50+. Doesn't matter if it is in neutral or in gear, clutch in or out. Doesn't seem to get better and only slightly worse with increase in speed. Also not gear dependent, will do it in 4th or 5th at same speed.
Let me give you a bit of background, vibration has always been there since I bought the truck in Dec '10. It has not changed much at all even after doing alot of normal maintenance. The truck has new rotors, pads, calipers, bearings(front), radius arm bushings and brackets, new drums, shoes and hardware, ebrake cables, new clutch kit, flywheel and slave, u-joints, plugs, wires, cap and rotor, and all new shocks. This was all routine maintenance and it needed all of it. It has changed vibes little to none. These have all been done in the last 500 or so miles.
I have searched and seen other problems such as tires( i have another set with wheels, no difference) and driveshaft mostly pointing to universals. Mine are new and are tight. Going to put it on the stands today and see if I get any wobble in the shaft in gear. Any other input, have grabbed the yoke and felt minimal play, not enough to cause the vibration in my eyes. Pinion angle ? Looks decent but I don't have a angle finder.... yet. Pinion nut is tight and no noticeable play. Any other known issues with vibration on these trucks ? I consider myself a competent mechanic(15+years) and have worked on many vehicle's, have owned 4 F150's of around this vintage but this has me stumped. Any help would be greatly appreciated, and sorry for the long winded post, just want to be thorough.

 

try turning the driveshaft 90 degrees, they have to go in the same way they came out

 

i had the exact same problem on the exact same truck. my passenger motor mount was jacked up and it went away when i changed it

 

@frenchy107, I always spray paint the edges to make sure they go in the same way they came out.
@Duct tape racing, will check it out here in a bit, just couldn't see it doing it so sparingly if it was a motor mount.

 

Well at lower speeds, that motor mount is the "push" mount versus the driver side being the pull mount so it basically has tension being pushed the whole time. Once it gets up to higher speeds, the mount has less push on it and sort of "planes out" causing it to vibrate if its worn out, loose, stripped ect.

 

my 94 had a bent axel and backing plate. I never realized it until the new shoes started wearing crooked. if you jack it up, and put it on jack stands, have someone watch the wheels to see if they run true. once I fixed the axel and backing plate the vibration dissapeared

 

Well, checked it all out and found nothing that I wanted to find. Put the truck on stands and put it in 1st thru 5th...... in 4th and 5th you would think I had a pack of elves tearing stuff up under there. Both rear axle bearing sound like they have had better days and I also have some grinding/noise coming from the middle/rear of trans. I'd say the rear is my vibration without a doubt..... where is that limited slip one I need anyway. The trans will have to wait til it dies, lol.

 

Just thought I would update for future reference. Replaced bearings, seals and fluid in the rear and the vibration is gone. 48 bucks well spent. Mind you, the truck made no normal signs of bearing failure, ie growl, grumble, grind, squeal etc..