lifted K5 vibration

[kujo]

i have a 4" trail master lift in my 90 blazer.. i hated the look of it sitting lower in the rear than the front from saggy stock rear springs so i added a leaf so its sitting pretty level now.. the problem is when i get up to 45-50mph it starts to vibrate a bit.. the lift in the rear is just blocks and they werent angled to raise the pinion.. i know this can cause vibration in some lifted rigs and shims are available to fix it, but i wanted to check with other blazer owners first.. i added 1" to the driveshaft also, ive done this many times with no vibration in other lifted rigs, thats why im not jumping to buy shims before i rule out the shaft..

to lenthen the shaft i cut it in our metal band saw (perfectly strait) after marking it so it was aligned the same as stock.. i machined a piece of steel that was the same size as the shaft in the center for the 1" addition, then stepped it down on each end so it was a tap fit inside the pipe for 1.5", and welded evenly all the way around as close to the rear joint as i could.. i also bored the inside so its perfectly ballanced.. like i said, ive done this before with no vibration, not to say its not the problem.. its also a bit worse when the hubs are locked and i didnt cut the front shaft, thats what leads me to believe it may be pinion angle..

basically what i want to know is if anyone had vibration they needed to fix with shims from a 4" lift and if so what shims did you use? i was leaning toward the 6* shims.. thanks

 

[gone huntin]

I had the same problem when I put the lift on my '90 Suburban. I tried shims, had the driveshaft lengthened, same stuff you did. Finally, after reading alot on here, I had H.A.D. build me a cv driveshaft for the rear and I haven't had any vibrations since (almost 6 yeaars now). You have more severe angle than I do because of your shorter wheelbase, so you would really benefit from one.

 

[4X4HIGH]

The problem with lifting a short wheel base rig is driveline angles and u-joint working angles. The t-case output and the rear axle pinion need to be parallel to each other and at the same time the working angle of the u-joint needs to be 3* or less. In a short wheel base vehicle it is nearly impossible to achieve both at the same time. The correct fix is a CV driveshaft but that also requires the pinion to point directly inline with the driveshaft (while driving, so 2* down from being inline is usually a good number so that it is pointing straight at the driveshaft while driving). If you don't want to spend the cash right now on a CV driveshaft i would first attempt dropping the t-case down about 1"-1.5" using a solid length spacer between the frame and crossmember. If this doesn't help much then add a rear axle shim.

I had the same issue when i lifted my rig and even after dropping the t-case and shimming the axle i got tired of going through u-joints so i finally bought a HAD CV driveshaft and now the problem is completely gone.

 

[kujo]

where do i get this HAD shaft? i dont even want to attempt the highway with it like this, i hate when something isnt perfectly smooth.. i already dropped the t case an inch, so i guess the next step is the shims or a new shaft.. thanks for the replys guys

 

[4X4HIGH]

You can reach HAD (High Angle Driveline) at www.highangledriveline.com or their phone number is 1-530-877-2875.

 

[kujo]

awsome, there is alot of good reading there.. now that i looked at that shaft, it looks alot like the stock front shaft with the cv joint.. has anyone put a slip yolk on the end of a front shaft and lengthened it to fit the rear? i have an extra front shaft, if its doable ill give it a shot..