Wierd Hum/Vibration
Logistics Pro
Joined: Jul 2001
Posts: 4,137
Likes: 41
From: Marble Falls, Texas
Is the truck 4x4? Lifted? We need a little more to work with. Right off the bat I would say driveshaft. chalk the tires, and put the truck in neutral. (to unload the drivetrain.) The truck may need to roll a couple of inches to unload. Once you do this, get under the truck and wiggle the driveshaft at every joint. And the carrier bearing too. There should be NO up/down side/side play at the ujoints. The carrier bearing is rubber hubbed, so it will move some. Your just looking for major slop. Also look for red dust on the ujoints. Any red dust and that ujoint is toast. The driveshaft itself will rotate back and fourth some. And make sure everything is greased well. The slip joint on these shafts have been know to cause vibration. That should get you started.
Logistics Pro
Joined: Jul 2001
Posts: 4,137
Likes: 41
From: Marble Falls, Texas
Okay, if it's 4x4...Make sure your hubs are unlocking. When you unlock them, you should be able to get under it and spin the driveshaft. But if you have an open diff, which most likely you do. You need to reach in the knuckles where the ujoints are (where the hub pivots) and spin the axles individually. They won't always spin the driveshaft since it's open diff. Just make sure you can spin both sides. Basicly what you are doing is eliminating any front axle driven component from the vibration problem. Worst case, pull the front driveshaft to eliminate it too.
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