Random vibration
 

Replaced the shocks, balanced the tires, when driving above 50mph I get a random cab vibration that shakes the bench hard and I can see the truck bed moving too, the steering wheel has the same vibration. I have now heard that the transmissions torq converters had issues that created vibration when they lock up. All suspension is tight and drive line doesn't have any movements....

Thoughts to look at?

Re: Random vibration
 

You've got to separate the various areas of the truck based on whether the problem is engine rpm related or vehicle speed related.

An engine run up to the problem rpm with the truck stopped will tell you if it's on the engine side or not.

Coasting through the problem speed with the engine off (or in neutral) will tell you if it's driveline or tire.

Once you make this determination you've eliminated a bunch of stuff you don't have to worry about.

If you can follow the thought process in these flow charts you can fix anything:

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

K

Re: Random vibration
 

well after a troll down the pavement this afternoon i dropped her into neutral and rolled free to allow rpm to drop to idle, vibration is still there so i will assume that it is no longer engine related. so i will go shake hard on the driveline and see if the carrier bearing is the issue or if any u-joints are sloppy.

Re: Random vibration
 

Go back to the last thing that was done to the truck prior to the vibration starting. I'm sure it didn't just happen out of the blue. Give us some clues and specs.

Re: Random vibration
 

If I knew I could, thats why i have been plugging away at ideas, just bought it, thought the stock wheels and tires had issues of balance, after balance still did it, bought new wheels and tires balanced and still there, replaced shocks, still there. now i know its not the motor, so suspension and drivetrain.

thank you all.

Re: Random vibration
 

One piece driveline or two?

Re: Random vibration
 

Weight come off driveshaft?

Re: Random vibration
 

Maybe a loose driveshaft yoke or loose pinion?

Could very well be a belt driveshaft or the driveshaft threw a weight like mentioned above

Also check your tranny mount

Re: Random vibration
 

I'd be willing to bet it's the driveshaft out of balance....

Re: Random vibration
 

I had an 87' GMC 3/4 4x4 about 10 yrs ago. It had a funny vibration at higher speed that kept getting worse. I figured out the vibe was still there when in nuetral and coasting on the highway. I checked everything and determined that the thin bushing that carries the yoke in the extension housing of the tranfercase was egged out some allowing the yoke to wobble around. You could feel the vibe through the whole truck. I replaced that bushing which wasnt that hard and the truck drove so smooth after that. It was Night & day difference.

That may not be your problem but thought I'd throw it out there

Re: Random vibration
 

Well done. Now if anyone comes on this thread and suggests a bad fan clutch, or out of balance fan (or converter) - or flexplate or harmonic balancer - you can disregard them.

Keep up the good work!

K

Re: Random vibration
 

at that speed and bench n bed moving, its the rear tires. just cause they were balanced doesn't mean they checked the rim run out. 1 good pot hole can bend a rim.

Re: Random vibration
 

I thought that about my stockers, so bought new wheels and tires, still there, highly impossible that the new ones are bad too and create the same vib. all of your suggestions are great. My rig is 2x4 so the transfer case issue i can rule out. i honestly think its either the driveshaft or yokes, after reading the sheets posted from Keith I can see how time can create bad shaft angles with run down joints.