I've posted this before, and I am stumped. I put new tires, (10 ply Sumitomo Encounters), on my all stock '96 4x4. It had a slight vibration on the old tires as well. The vibration, (which comes and goes and isn't felt in the steering wheel), was worse with the new tires which I had re-balanced 2 more times. I replaced the center bearing, all 3 universals, and had on of the best suspension guys in the area look it over. All looked good except for my lousy shocks. I hoped the old shocks were so bad they couldn't dampen the springs, so I installed a set of Bilstein shocks today. The issue is still there. It almost HAS to be the tires...or am I overlooking something?

 

You didn't mention wheel bearings... how old are they? How much play do they have?

 

The front bearings aren't all that old. Not much play at all. I bought the truck from my Dad who bought it new. It has around 123,000 miles on it. It's an odd feeling vibration. The sensation is almost like going down a washboard road while towing an unloaded trailer. It feels like almost all of it is coming from the rear of the truck.

 

I've seen wheel bearings that are toast at those miles.... but you should be feeling it in the steering.

Check ujoints, driveshaft hanger bearing, pinion bearings (usually seal leaks too.)

 

The center bearings and universals are brand new.

 

Sorry, I didn't read your first post thoroughly enough

Is it under acceleration, coasting, deceleration? Going straight or turning?

For the pinion, just grab the yoke and try to force it up/down and side to side, just to see if there's play.

Maybe rotate the tires?... see if the problem moves around?

 

We recently did the rear 2 piece drive shaft universal joints and center bearing on my son's 2001 dually, afterwards he complained of a vibration. WE looked everything over but the vibration remained. WE had to install a new yolk and pinion seal and while we had the drive shaft down we discovered that the slip joint between the two driveshafts was too tight. While removing the center bearing race we had slightly flattened the male end that has the splines, we tried cleaning up with a file but was still too tight so finally took an angle grinder to the very end and all was good, vibration gone.

 

Generally there are only two types of vibrations.....and will be from completely different sources too.
Slow wobbly vibrations described like a washing machine on a spin cycle are related to slower moving components like tires, brakes, bearings, etc...

Fast harmonic vibrations described like a massaging tool are related to faster moving components like engine, transmission, driveline, u-joints, etc...

Which one would you say yours is?

 

I would say slow and wobbly. I feel it under braking sometimes as well. It's really an odd sensation.......almost a loping feeling. It doesn't have to be going very fast to happen. It comes and goes, but you feel it more often than not.

 

Sounds like bad tires or tires out of round or tires separating internally. "New" doesnt mean they're good, especially with some cheap tires available.

My suggestion would be to take it back to the tire shop and tell them you want these new tires road force balanced to determine whether or not the casing needs to be 180* on the rim or if there's a tread/casing separation issue which a road force machine should be able to detect.

In saying that, check and see how much weight they used to balance the tires. If you see more than a couple ounces per tire or side then thats an indication that the tire is just too out of round to balance correctly, or the techs dont know what they're doing.

Another thing to look for is cross balancing of the weights. If there's more than one weight on one side of the tire and are not together but rather placed far from each other, that means the tech doesn't know how to balance a tire.

 

They're Sumitomo Encounter tires, and according to the reviews, they're pretty good. That doesn't mean I got a lousy set, though. They were originally force balanced. I took it back and they checked them again, moving one tire 180 degrees. Didn't fix anything. I took them to a small, independent shop that has a reputation for fixing issues. They made it better, but the tech said it took more weight than he was happy about, and he "thought" that 2 of them were slightly out of round. I've played with pressures, rotated them and the problem still exists. Thanks for the input!

 

WILD GUESS would be u joint timing

https://www.youtube.com/watch?v=gmV4qwLfOMY




















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It went back together in the same orientation we took it apart. I did notice while under the truck that the rear is actually a bit offset to drivers side, which seems odd. It's never been wrecked, so I assume it's a factory thing.

 

Drums could be out of round and/or balance. If they ever got hung up and hot it's easy to warp them.

 

Driveline always looks a little off as the differential doesnt sit exactly in line with the transfer case.

And another way to inspect tires is to jack up the rear axle and set it on stands. Then with someone in the truck "whom you trust", start the engine and put it in gear with you watching the rear tires for movement and roundness. If there's any hop from weight issues you should see it. Again, I cant stress enough that you need to be safe doing this because if the truck comes off the jacks then because of the immense 300 lbs of off idle torque the Cummins generates, the truck will continue to propel itself forward no matter if you have your foot on the brake or not. The only way to stop it would be to shut the engine down.