Drivetrain vibration

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dnuccio

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I've got a vibration in my 97 Suburban K2500. You can barely start to feel it at about 55mph, gets very noticeable at 65, its worst at 75, then smooths out ALOT at 80+. Tires are a month old, and I've had them re-balanced 2 times. The rear driveshaft has brand new u joints and was just balanced. I don't think its the front driveshaft because removing it makes no difference. I have not yet checked motor mounts or the trans mount. I was thinking it could possibly be the shocks. The truck sat for a while before I bought it and the tires it had on it were flat spotted really badly, to the point that the truck was impossible to drive above 40mph due to the tires making it shake violently. My thought was that this violent shaking could have wiped out the shocks. The shocks do look old, but don't appear to be leaking or anything like that. The truck rides smooth (as smooth as a 3/4 ton anyway) up to 50mph. Opinions?
Thanks
 

dnuccio

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Update: Replaced the rear shocks today, the old ones were definitely shot. Truck rides a little better, but the vibration is still there.
 

Bob L

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Check to be sure the rear u joint is perfectly centered in the pinion saddle I have had that give me a vibration in the past.
 

TylerZ281500

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so drivehsaft balance means nothing, new u joints means nada if they weent set properly. Why do i say that? a perfectly straight drivehsaft with good u joints has no part error, requires no wieght, it is almost perfectly balanced in every sense. if they balanced it then thats all fine and dandy until the u joint decides its gonna be impartial to the fact that your yolk is running out a few thou in all three placs at different directions.

what id do....grab yourself a magnetic dial indicator, clean a nice spot on your driveshaft, center and both weld yolks closes to the weld. measure the runout, pull the shaft out, reset the u joints, hopefully they were installed properly? then id start checking pinion runout and play as well as any play in the transfer case output.

you mentioned the truck sat and thought the tires has flat spots? they could, or did you replace those tires so these tires are new new?

why was the truck parked? did it have this vibration before it was parked? bent rim? bent axle shaft?
 

90halfton

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Check wheels for mud inside the rim. Normally happens in duallys more than single wheels, still happens though, and it's an easy check.
 

tom joyce

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I had the same thing with my k2500 pickup. I changed everything, including the differential spider gears....Then the problem became obvious.
The cage that hold the steel balls inside of the half shaft CV joints had little cracks in them. A piece finally busted through the boot, and I got the 'death wobble'. So I changed both half shafts and the vibration went away.
I tore the boot off the (seemingly) good shaft and found the same hairline cracks in the cages.
 
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