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help me identify this vibration.....

rayc

Full Member
Joined
Aug 17, 2003
Messages
281
Loc.
Western Oregon
I have a pulsing vibration which feels like it is coming from the rear end area. It starts around 50-55 mph and gets faster if I hit the accelerator. It stops when I let up on the gas completely.

I had my rear end rebuilt a year and a half ago and have less than 1,500 miles on it. The drive line and U-joints seem to be o.k. and I actually had them replaced about 8,000 miles ago along with a shim kit to get it to line up properly.

I am no mechanic and any help would be appreciated.

Thanks in advance
 

bax

Contributor
Old Member
Joined
Aug 22, 2005
Messages
14,491
8000 miles is a lot of miles on a u joint for a lifted truck. I would check the u joints first.
 
OP
OP
rayc

rayc

Full Member
Joined
Aug 17, 2003
Messages
281
Loc.
Western Oregon
Thanks, I hope that is the problem. It would be considerably cheaper than other stuff I could imagine....:)
 

70_Steve

Old Guy
Joined
Dec 13, 2002
Messages
8,317
Check your pinion angle. When under power the pinion tends to be forced down, increasing pinion angle. When coasting, the pinion lifts, decreasing pinion angle. The difference between the two angles might be enough to cause vibration under power, and no vibration when coasting.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,346
Yep. What they said.
Another thing to try right this minute (if you haven't already) is to get some new lube into all the joints AND the little female zerk-fitting that's kind of semi-hidden in between the two joints up at the CV/Double-Cardan end.
It takes care of the centering ball and is often overlooked.

Also, check your u-bolts holding the joints for looseness OR over-tightness. Over-torquing them can shorten the life of the joints.

And speaking of u-bolts, check the main springs ones too. One of your shims may have cracked if they're aluminum and your bolts might just be loosening up naturally anyway. It's not unheard of.

While you're under there, check to make sure that your pinion nut is not backing off. THAT's not unheard of either. And you did just have the rear end done not that long ago. So it's another good thing to double-check.

What you're describing does indeed sound like u-joints though. Probably slowly going out on you and creating the vibration. They'll just get worse though. If greasing them helps, great. But it's just a temporary measure as the damage has already been done and you're going to be better off just replacing all three and closely inspecting that centering yoke for any wear. Replace it too if necessary.

Paul
 

bronko69er

EB Addict
Joined
Oct 16, 2006
Messages
4,599
Loc.
Renton, WA
Check your pinion angle. When under power the pinion tends to be forced up, decreasing pinion angle. (When shimmed properly) When coasting, the pinion drops, increasing pinion angle. The difference between the two angles might be enough to cause vibration under power, and no vibration when coasting.

Fixed it for you. ;D
 
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