bad shake in rear of truck from 55ish to 65 ish

[colonel mustard]

heres the truck specs.

1982 k5
14 bolt swap
6" lift
double cardon high angle driveshaft.

the shake: its a left to right feeling out of the rear of the truck. its not through the steering wheel at all. at 50ish mph it is at its worse and smooths out out (but not all the way) around 65ish mph. sounds like a balance issue right??

before the 14 bolt swap there was no shaking, so that eliminates the driveshaft being a source....but maybe not the pinion angle.

right now my pinion points DIRECTLY to the tcase tail shaft. I used a 6* shim to make this happen. my first thought was maybe taking out the 6* shim and using a 4* shim. im thinking maybe underload, the springs are soft enough to change the pinion angle enough to cause the shake....just a thought

im using balance beads. I have used them for years....8oz per tire per manufacturer. the driver rear only has 4 oz in it however. the order was wrong and I haven't received my corrected weight in the mail yet...but could only 4oz cause this much shake ???

also, I believe it from the shaking, I have developed a pinion seal leak. blahhhhhh. so if anyone has advice on replacing the pinion seal I would love to hear it. is it a good idea to replace the pinion bearing as well? thanks in advance.

 

[Customblue]

I would think that it would be a driveline issue not a balance issue if it has caused your pinion seal to go bad.

 

[dvdswan]

Check for dried mud on your inside rims.

 

[colonel mustard]

Check for dried mud on your inside rims.

did that but it actually has been doing it since before I took it wheeling. I trhink im going to try a lesser degree axle shim and see if that heps

 

[colonel mustard]

update:

I removed the 1" tcase spacers the previous owner installed. im assuming he installed them to correct pinion angle at one time. removing the spacers raised the tcase 1" and changed my pinion angle by 2 degrees. the shake is much less now but still there. now, however it feels like a balancing issue. I will add the rest of the 4oz of beads in the driverside rear tonight and see if that helps. my suspicion is it will.

 

[Frankenchevy]

Could be coincidental that your pinion seal started leaking, but that points more to driveline vibration than tire balance. Tire balance usually produces an up and down vibration because that’s the plane it travels in. I’d think that’d cook your shock before your pinion seal. When was the last time your pinion seal was replaced?

Mine didn’t leak at all, but the truck sat for over a year while working on it and I believe it just hardened. A leak started a few weeks after I put it back on the road and kept getting worse. New seal, new u-joints, problem solved. My situation was more simple due to the stock nature of my truck's driveline angles.

I don’t think you want the pinion pointing straight at the t-case. When you’re driving forward, it’d make sense that the axle housing rotation would be counter to the tire rotation—so as the tires rotate top towards the front of the vehicle, the axle would rotate top towards the back of the vehicle. That would point the pinion even higher up, maybe even starving it of lubrication, but I may be way wrong. Just thinking through it using physics.

 

[75gmck25]

I had very pronounced side to side vibration at about 40 mph with a Dodge I used to have, it it turned out to be belts in the tire that had broken loose. If you drove it slowly forward or jacked it up and rotated the tire, you could seen the tread pattern swing left and right as the tire rotated.

Bruce

 

[Frankenchevy]

That sounds unnerving Bruce, did you replace those puppies immediately?

Steven , one thing I forgot to mention, though you’re probably ahead of me on this, is all your suspension stuff since you’ve recently swapped axles. After a few hundred miles, you’re supposed to recheck torque on everything...ubolts, etc.

And I believe your tires are brand new, but if not...what Bruce said.

 

[TubeTruck]

Is the 14 bolt a full float or semi float? If semi I would check for a bent axle shaft. Maybe a bent hub?

 

[Badger505]

I would check the tires. I have issues in with the beads getting moisture and clumping together.

 

[Badger505]

I would check the tires. I have issues in with the beads getting moisture and clumping together.

 

[Knuck55]

My experience is that when you have a drive line issue the frequency of the vibration in much faster than a wheel balance issue. In other words your driveshaft is making many more turns than your wheels are so it will be more of a fast vibration rather than a shake. Wheel balance issues are much more pronounced in the 45 to 55 MPH range. Hope this helps.

 

[Richard Schultz]

Check your clearance on your ring and pinion,sounds like something is loose.

 

[shiftpro]

I don’t think you want the pinion pointing straight at the t-case.

This is fine with the CV off the transfer case and regular U joint at the bottom, slip joint in the drive shaft.
But under load or torque the pinion shouldn't point any higher than the CV in front. If you have really flexy springs and no traction/anti wrap bar then a big foot in the carb will allow the pinion to point above the CV and vibration can be felt. But this wouldn't happen on the highway normally.

Steve check if your pinion is pointing a little higher than the CV. It could be possible the torque around 50 mph has the pinion pointing a bit too high. You can mount a GoPro underneath and video the pinion while you take your truck through it's paces.

 

[Rusty Nail]

Four ounces of tire balance is an absolute ASSLOAD.