Another vibration thread?

[Chris Ziemer]

My 82 K5 has a pretty decent vibration at about 15 mph. I searched the threads and just didn’t see anything that hit home.
I’m at a bit of a loss here. 4” lift, springs and blocks (on when bought). It had the stock driveline (w/slip yoke), so I took it in to have it balanced and lengthened (came with new u-joints). Done and done. Still vibrating. Took the driveline back, re-balanced it. Done. Still vibrating. Then I flipped the driveline 180 degrees. No change. Balanced tires. No change.
It vibrates about 65mph too, but that’s about warp speed for me.
Replaced the trans mount, but that actually just increased the angle, b/c the old mount was oil soaked and sagging.
Vibration at 15 and 65mph. Related? Any advice is very welcome.

 

[obijuank5]

Usual suspect is rear driveline related. After a 4” on a blazer a CV style rear driveshaft can get rid of those vibes. Typically the lift kits would come with instructions to lower the trans crossmember to help with these vibes.
That’s not a great way of doing it long term but it is an option for you to see if it changes your outcome.
Change position of the trans crossmember relative to frame and see if it changes your vibes.
This is just a test to see if lowering the crossmember alleviates these vibes.

 

[Blue85]

Measure the angles - T-case output and axle pinion. With the transmission in neutral, check for play in the slip yoke. As @obijuank5 said, you're probably at the point where it may never be perfect with a stock-type driveshaft, but knowing the angles is the place to start. Are you running 1330 yokes? You're probably above the "rated" working angle for the joint and the only thing that helps with that aspect is lengthening the driveline - i.e. S.Y.E. SYE + CV is the ultimate solution, but you don't know yet if you'll have to go that far.

Also, if you can borrow a set of wheels and tires as an experiment, that might be worthwhile.

 

[ZooMad75]

East way to tell if it’s the rear shaft angles. Yank the shaft out kick the t-case lever in 4 high and lock the hubs in. Go for a drive.

If the vibration is gone you have a problem out back. Like the others had said usually the combo of 4” lift with a slip yoke t-case output is going to end up with horrible u-joint angles.

It’s odd to me that length needed to be added to the rear shaft.

In a perfect world you’d have no more than 2 degrees difference between the two angles. It’s probably off much more than that.

I’d also had a pretty noticeable rumble noise on deceleration that I though was the fresh knobby tires I had. It was not the tires. It was the rear u-joint trying to escape the yoke at the axle. It partially succeeded as I coasted to a stop. Drove home with the front drive and bingo the noise was gon on decel and no higher speed vibration either.

Just remember to shove something over the end of the slip yoke housing to keep it from loosing fluid.

 

[Chickntrk]

Use an angle finder and measure the angle at the front u joint and the back I joint, they need to cancel each other….sometimes people add shims to the rear which makes the angle at the pinion less than that at the t case and actually causes vibes. CV driveshaft the pinion should be in line with the shaft, regular shaft the pinion angle and the t case angle need to be the same to cancel each other.

 

[Blue85]

East way to tell if it’s the rear shaft angles. Yank the shaft out kick the t-case lever in 4 high and lock the hubs in. Go for a drive.

Just remember to shove something over the end of the slip yoke housing to keep it from loosing fluid.

Yeah, this can work, assuming everything is good with the fro t driveline. Also kind of critical to find some way to hold the fluid in (disclaimer: I have done it). Still not first step before checking the angles.

Use an angle finder and measure the angle at the front u joint and the back joint

Right, like was already said.

 

[Wes Harden]

Has lift blocks, some if not most come with an angle built in. I'm sure the lift kit builder just guestimates the angle.

 

[83ChevyK5Blazer]

When I did the first lift on my k5 it was a 4 inch block lift out back. It gave me driveline vibrations.

 

[Chickntrk]

Has lift blocks, some if not most come with an angle built in. I'm sure the lift kit builder just guestimates the angle.

On the other hand if it doesn’t have angle built in that could be the issue as well….4” with no pinion correction would almost certainly give vibes on a blazer

 

[dyeager535]

Has lift blocks, some if not most come with an angle built in. I'm sure the lift kit builder just guestimates the angle.

Except that won't fix the angle at the t-case. You will reduce the working angle of the joints, but you introduce the problem of mis-matched u-joint operating angles.

OP, if this stuff is new,

 

[Wes Harden]

not saying it was the solution. Just another angle to think about that may or may not be helpful

 

[dyeager535]

As said earlier, measuring the angles is the first step, really just speculation until that happens.

4" lift with such a short driveshaft generally seems to be a bad idea without a CV, or at least doing something to get the angles more appropriate like dropping the t-case. But even then, the angles need to be right.

 

[ramack]

My 82 K5 has a pretty decent vibration at about 15 mph. I searched the threads and just didn’t see anything that hit home.
I’m at a bit of a loss here. 4” lift, springs and blocks (on when bought). It had the stock driveline (w/slip yoke), so I took it in to have it balanced and lengthened (came with new u-joints). Done and done. Still vibrating. Took the driveline back, re-balanced it. Done. Still vibrating. Then I flipped the driveline 180 degrees. No change. Balanced tires. No change.
It vibrates about 65mph too, but that’s about warp speed for me.
Replaced the trans mount, but that actually just increased the angle, b/c the old mount was oil soaked and sagging.
Vibration at 15 and 65mph. Related? Any advice is very welcome.

Stupid question. Is it a new issue, started after the lift, etc?