Vibration at freeway speeds?? Help

[platapus]

I have a 79 K5 w/ 4" lift and 35s. At about 40MPH on up it begins to vibrate the truck, in a pulsing pattern. It runs smooth, the grows into an annoying vibration then tappers back down over the corse of about 10 secs. It does this over and over. I has done this since I bought it about a year ago.

I just put a new crate motor in it. I figured it was tire related, so I put brand new rims and tires, still no help, I had the drive shaft legthened to the proper size for a 4" lift (this was never done) and had the drive shaft rebalanced. THis helped a little, but I still have the same problem?

I have locking hubs, so the front drive train does now move at all while driving.

What else could it be. could the rear axle shafts be bent? or un blalaced?

 

[bigblazer87]

How's your pinion angle?

 

[onetonbb74]

do you have swampers, thatll do it for sure brand new or not. If your transfercase is a np203, it spins the front shaft the entire time you drive and that could be the culprit.

 

[onetonbb74]

id check the tow on the front axle and any/all steering components for loose or damaged parts as well as the shackle bushings as these always get overlooked. Im pretty sure its the swampers, i drove accross country in a 79 pickup a couple years ago and no vibrations at all until 80mph+ on stock tires 235/75/15's. Everything changed when i put 36" swampers on the same truck with no lift and the shimmying vibes started even when the tires were brand new.

 

[Cornfield creations]

I have a 79 4" on 33's. I had pretty bad vibes until I gave jesse at HAD a call. With my 1350 CV shaft, I can cruise at 90 with very little vibrations. Not saying I do, just that it can if wanted to.

 

[BL1TZKRIEG]

can a worn slip yoke cause a vib ?

 

[dhcomp]

yep

 

[platapus]

I have tsl/sx. IT also vibrates the same way with my MT baja belted. I havw a NP 203 with a convertion kit. I have a new drive shaft, new CV joints, and the entire setup was just rebalanced yesterday.