First of all let me say that this a wonderful forum. ........here's my problem

1991 Runner 4x4.......156,000 miles.......i'm getting this awful noise/hum when I drive.....the problem just started maybe a week ago.....to describe to the noise best it sounds like a constant 80hz bass tone when on the gas....if i left off it goes away.....at the same point there's a vibration that seems like it may be coming from the rear end but it's hard to tell......the vibration comes and goes with the hum...,,,it's expecially present at the 55-65mph range......in conjunction with that the truck really feels "loose" like the steering or wheels are loose.....i've checked the wheels i.e. air pressure...balanced....that's all fine....i've searched the forum and seen everything from idler arm to rear wheel bearings.....would a bad idler arm make the truck do the shimmy shake @ 55-60? whatever the problem is it seems to only rear its head when i accelerate....i was thinking maybe the driveshaft is out of balance but doesn't a drive shaft spin when decelerating?.. ..i would greatly appreciate any insight you could shed on the subject.....

 

Sounds to me like your U-Joints are shot ! Cheap easy fix too...

I replace mine once or twice a year But I wheel the H.. E.. Double Hockey Sticks
(HELL) outta my rig.

 

So my u joints are the cause of all of my problems? Is there any other parts I should look into replacing since I'm under there?

 

Since your going to have to take the driveshaft out to do this repair, you may aswell replace the differantual seal. Its like a 3 dollar seal, and it will leak eventually.

Also soak the 8 bolts and the flange down with PB Blaster a couple days before hand. This will make life allot easier.

Im sure someone else will chime in here ???

 

Pull the rear shaft off and drive around in 4H for a bit. If the vibration is gone, you've found your problem. I second the PB Blaster and also recommend a cheater bar on your wrench to help save your knuckles.