379 peterbilt problems

All new U-joints and hanger bearing. Wheels are good. It feels to me like it's more than just shaking... even at slow speeds when I hit bumps, even small ones, the whole truck shudders. Almost like I have no suspension. And of course it shakes at highway speeds too. Even on smooth roads. I had this problem with a 97 pete I used to have. I never found the problem with that one. Wound up trading it in. Thanks for the help... there has to be a solution. It really doesn't feel like a driveline problem. It feels more like suspension but all that is new too. Changing the bushings back there is what started this problem.

 

Are the shock absorbers ok? Is the diff lock released all the way? How about a loose yoke or loose wheel bearing? What about the ride height or leveling valve? If I think of anything else I'll post it here.

 

Yeah, new shocks, New diff. New leveling valve. Ride height is good. Yokes and wheel bearings all tight. Thanks!

 

Have you checked the wheel assy. For runout both radial and axial. Sometimes the hubs or wheels can be worn which will cause an off-centered installation. Check the drums also to make sure that they are centered on the hub. Keep in mind there will always be some runout but what you are looking for is more along the lines of excessive runout. Hope this helps and good luck to you.

 

Sometimes on older Pete's if someone doesn't drop the air suspension under a heavy load and just pulls out it can bend the leveling arm and throw off the suspension causing it to act like the divider is screwed up. Look to see if it's been bent.

 

Also in rare cases the arm will flip over and needs to be removed then put the way it was. I saw a guy trying to figure out why it was like that one day at a drop yard but he could not fess up that he didn't drop the suspension and just pulled out under a heavy load. His leveling arm flipped around.

 

I don't know if you're talking about a driveline vibiration or a suspension problem. You mentioned your problem started when you did rear suspension bushings. Did you take the driveshafts out at that time? Did you pull them apart? If you did, you may have put them back out of phase. Doing this will cause all kinds of trouble, and unless you look close, everything will look right.



Look at the driveshaft I posted. Notice that the u-joint caps that are mounted in the driveshaft section are both lined up exactly with each other. If out of phase, the shaft will have been put back 1/4 turn off. The u-joint caps will still align, but one end will be the cap mounted in the driveshaft, and the cap on the opposite end will be the one mounted in the yoke. Even experienced mechanics have done this before by dropping just one end of a driveshaft and sliding it back together without noticing the wrong caps are aligned.

Even if the right caps are facing each other, make sure they are exactly aligned. They could be one spline off, or the shaft could be twisted causing mis-alignment.

 

I'm with Davidlee. Sounds like a tire problem, probably a drive tire or wheel out of round. Shakes are more of a tire issue. Driveshafts spin about 4 times faster than the tires. Any problems with the driveline is felt more like a buzz or hum. Driveline vibrations usually change with engine load, or being in gear vs neutral.

 

Well, I've put on all brand new Michelin XDN2 Drive tires. Still shaking, shuddering when I hit bumps. Just a steady shaking when I'm on smooth highway. I'm convinced it is a suspension problem. Has anyone ever heard of "Spring Balancing?" That is something that was mentioned to me today but the guy didn't know exactly what it involved. Just that he had heard about it. Someone else said something about adjusting the springs? I also had the alignment checked and it is on the money. All three axles.

Had the driveshaft straightened and re-balanced at Randy's Driveshaft Service in Houston. They also put it in phase. Then I replaced the short driveshaft between the rear ends with a brand new one from Peterbilt. All new u-joints and hanger bearing.

 

Do your brakes pulse when slowing ? I wonder if a warped drum could cause this.
Did you balance your new tires ? see them spun on the machine yourself ?