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I have the 87 F250 4x4 with a 5.0/auto/AOD. Around 45 MPH, I start to feel a vibration that gets worse as the MPH increases. It gets so bad that the sliding rear window shakes and rattles. When I let off the gas and coast, the vibration goes away and it is smooth as ever. Even if I touch the gas a bit, the vibration/rumbling comes back. I seem to feel it right under the drivers floorpan, but it might be everywhere. Any thoughts? It only happens under load, and the 4WD is disengaged. I thought uit might be the transfer case but does that happen if the 4WD is not on? Manual hubs, 100,000 miles APPROX. PLEASE HELP!!!
Check/Replace your driveshaft u-joints. I had EXACTLY the same problem. Grinding/Shaking under ANY load, and nothing if I took my foot off the gas. Good Luck. (get the greasable ones if you have to change em too!)
[updated:LAST EDITED ON 04-Dec-01 AT 10:05 PM (EST)]The front drive shaft will not turn if the hubs are locked out and 4x4 disengaged. I think the front drive shaft spins a little when you are moving, but should not spin much, I’m not sure though. Someone will probably correct me if I’m wrong.
Now a story: I just changed my front drive shaft u joints the other day, and they were bad. One of the ends didn’t have and needle bearings in it, and two others were frozen. I did not have any problem with vibrations at all; I just changed them because they were original ford.
Madman is right... The drive shaft will spin a little in the front when driving but will not cause the noise you are explaining. Unless of course you have a hub problem which would cause it to spin!