Troubleshooting driveline vibration 91

[RJB44]

Went to see the folks at a local Off-Road shop to see if they could help me diagnose a vibration issue. The issue is, when I accelerate from a stop I have a hard vibration throughout the truck. It is most noticeable under load between 10-30 MPH. It is still there at highway speeds (45-60mph), but not as noticeable. I have a 4-inch lift (all springs) and 35-Inch tires. I had the driver shaft professionally lengthened and balanced, but the problem is still there. I have replaced the u-joints a couple of times, no change. The guys at the shop suggested that I replace two motor mounts, the transmissions mounts, and add a set of traction bars. I can understand the mounts, if bad, but traction bars? My feeling is that something is wrong somewhere, and that traction bars are designed as an add-on, not something that will correct a driveline problem. The vibration is not present when not under acceleration.

Your thoughts?
Thanks

 

[gone huntin]

Has it been there since the lift was installed? Have you checked your angles? I had a vibration after installing a 4" lift on my "90 Suburban. I tried degree shims and drive shaft balancing, but I finally had to put a rear cv shaft in it from HAD to resolve it.

 

[4X4HIGH]

Sounds like improper u-joint angles. It is hard on a short wheel base vehicle to get the proper u-joint angles AND the proper working angle at the same time, you can usually only get one or the other. Having matching angles will eliminate a vibration but having more than the maximum u-joint working angle will eat u-joints. The solution is a CV driveshaft.

 

[Stomper]

U-joint angle sounds like the problem. Under acceleration your pinion angle changes (axle wrap) therefor making the vibration worse. The traction bar would help but it won't fix the problem and is more of a mask. I agree with Scott that a CV shaft would be the best fix....You'll still need to make sure that the angles are correct in either case.