I'm curious Joe, did you lift the truck off all fours and run the truck to see if you can see any vibration at 50 mph? Not sure if you have shops near you that build street rods, they can tell you real fast if the engine is offset or not. They deal with that stuff all day long. Good luck bro...

 

I set the angle of the rear end at 3 degrees up which paralleled the 3 dgrees down from the tranny. Could it be that it is fine up to a certain speed but after that speed is flexing up enough to change the pinion angle to cause an inherent vibration? Am running four leafs on the spring pack for the rear.

 

No Ed and that is probably my next move. Have beat this horse until it is dead and don't seem to be gaining on it.

 

I really doubt it! I have the same setup on my truck Joe and it doesn't have the shimmy at any speed. My rear end is at about 4 degrees from the tranny. I don't think 1 degree will do anything. Come to think about it my leaf springs are shot in the rear too. There shouldn't be any flex at 50mph and there is no torque happening at that speed. Something is causing the vibration at cruising speeds?

 

I'm gonna make a phone call for ya, I'll email you later.
Ed

 

thanks Ed appreciate it

 

Hey just curious, are your U-joints in "Time" I've seen shops shorten drive shafts, and not get the U-joints in line with one another, and cause all sorts of vibrations? Just a thought? You don't think you have a bad U-joint or something along that line do ya? Let us know

 

Joe, what is your gut feeling? Are you making the problem better? You're starting to make me think it might be something else that driveshaft. A buddy had a new car years ago that he thought had a trany vibration at 40 mph and above. It turned out, on the third visit to the dealer, to be an off-center wheel. Keep us posted. Jag

 

I know that you have been over your truck countless times in the last year or so fighting this problem. The frustration level must be through the roof. It might be time to take a step back, take a few deep breaths and start from square one.

A buddy of mine was fighting something similar, Jag's posting just brought it to mind. He built a Daimond T roll back truck on a large truck chassis. The truck had a vibration about cruising speed....65 or so. He messed around for about a year and a half, replacing tires and wheels (not cheap for a couple ton truck) re-analyzed the driveline, etc.....pretty much everything you have done. One day we were working on it and had the rear of the truck up on stands with the rear wheels removed. With the truck running in gear you could actually see the run out of the rear drum. Of course since this was a large truck axle with a full floating rear axle, the rear hub/drum assy was a huge monster (which translates into expensive) He had to pay almost $400 each for new rear hubs. Basically the machining process back at the factory wasn't very acurate and the center hole wasn't in the center, causing a wobble of the rear hubs.

I think the suggestions of putting your truck up on stands (good sturdy ones) and seeing if you still have a vibration is a great idea. That would eliminate the front wheels. Try it with the tires and wheels on the truck and with them removed.

Don't overlook the simple things, if you're like me you're prone to overthinking the situation and overlooking the small things

Bobby

 

Make sure that at speed your drive shaft isn't hitting the trans. The pig comes up and makes it ever so much shorter when under power. If you were close to all the way in you could be going in and the yoke bottoming out.
Max

 

Engine offset is not a problem unless the crank centerline is not parallel to frame. Fortunately the frames in our trucks are straight and parallel, so you just need to measure from the crankshaft pully centerbolt to the frame and from the center of the tranny output shaft to the frame to see if it is parallel. If that checks out then the next thing to do is to pull the driveshaft and have the balance and straightness checked. (AND that the ends are in phase!) then replace the universals, running them out of alignment before may have damaged the bearings. One more thing, when you reset the pinion angle you did do it at normal ride height with the full weight on the wheels, right? For those following along, you need to do this on a drive on lift, or lacking same put the truck wheels up on 4 equal height drive-up ramps until you check the angle and tack the axle perches in place. The pinion angle should match the engine crankshaft angle at normal ride height, they should NOT point directly at each other!

 

Bias ply tires are notorious for being out of round or the belts slipping.

 

Joe, AX has some excellent info here... If I recall? Didn't you have the driveshaft shortened or something and then balanced? Maybe they didn't put back together correctly and the ends are not in phase as AX and Truxx mentioned. Just a thought!

 

Thanks guys for all the advice, yeah am pretty frustrated. Plan tonight to put the rear up on stands and remove the tires and see what I have. Am starting to think it may be axle, have almost eliminated everything else. Will keep you posted.

 

Joe,

Once you get it on the stands have someone run it up to speed while you check the tire and wheel assy for runout. Then repeat the process witht he wheels removed and looking at the drums for runout. Finally, remove the brake drums and check the axle hubs for runout as well.
It's not unheard of to have a brake drum out of round or out of balance.

Bobby