Help, bad vibration

I need some help. I have a 1947 IHC truck. It's sitting on an 85 s10 frame. 327 350 turbo 10 bolt open rear. Here is the problem, when I'm driving the truck at about 35MPH and higher I get a real bad vibration. You can feel it in the steering wheel, in the floor, as a matter of fact the whole truck seems to vibrate. When you get off the gas it seems to lesson but not much. The vibration happens in all 3 gears when the truck is vibrating and throw it into neutral and coast the vibration goes away. I thought it was wheel bearings, i replaced all 4. It must be something in the drive line. Any help, suggestions, or advice on what could be the cause of the problem would be greatly appreciated.
Thank you,
Rod

 

Investigate your drive line angles, condition of the drive shaft (phasing and balance and universal joints) there are plenty of threads on the HAMB regarding this.

 

my first guess would be wheel balance, then front end pieces (tie rods, links, pitman arm ect.) Then Driveshaft balance.

 

it is usually what you just worked on........ that being said, chronisterracing is a good place to start

 

Its going to be either the drive shaft itself, pinion angle, or the u-joints from what you're describing.

See, when you put it under load (gas pedal depressed) you are causing it to either bind, or have the u-joint throw itself off balance which will cause the nasty vibration. When you let off the pedal, the shaft may be slipping into the 'safe' space in the joint which allows it to no longer vibrate.

You may also be out of whack with your pinion angles as well, since it does vibrate under load and not when you let off the pedal. I believe when you set up the rear it is supposed to have a slight 'down pitch' on the input yoke on the rear end, which allows it to move up to either zero or 1 degree when under load. However, you springs shouldn't allow the rear to move that much unless they are extremely softly rated. And, I'm talking about leaf springs here, so if you're using a 4-link and coil overs, you probably won't have this problem or issue.

My advice is to check the U-joints. Chances are you'll find your problem with them. Post pictures of your setup and the driveline and we may be able to help you more from there.

 

How far in is your driveshaft yoke into the 350? If it is really in there it may be possible that under load the yoke could be bottoming in the transmission. Just a thought.

It definitely has something to do with load, as it does this at various speeds and in lower gears.

BTW: Fix it, and put on Beachboys GOOD VIBRATIONS! LOL

 

I also would think the problem is with the drive shaft. Check u-joints, angles, and if the u-joints are in time with each other.

Neal

 

As already stated, definately would check the u joints.

 

I had a simular situation in a 68 Charger..turned out the Previous owner put the wrong torque converter in..it wasnt balanced.

It sounds like a drive train balance issue somewhere..Drive shaft, Torque converter, harmonic balancer..
miss matched parts

also check see if your torque converter bolts are tight

check your U joint phasing..

or U joint not aligned correctly when installed

 

exhaust pipes could be comming in contact with the frame.when you let off the throttle the engine relaxes down so to speak,check the p*** side.

 

Thank you all for your time and help! I will take a look at all of your suggestions. Again thank you for youir help, it's greatly appreciated. Rod

 

Sounds like u-joints. Also check the rear pinion bearing. If that seal is leaking, could be that rear u-joint.

 

make sure torque convertor bolts are tight .also check u joints