Holy Moly ... I don't mean to hijack this thread but maybe this will add to the discussion. I have the exact specific symptom U9000 cited ... a vibration at approx. 45 - 50 mph, in the seat of my pants suggesting something out of whack at rear of truck. The vibration seems to be lessened when under load i.e. 2500# truck camper:

Here's what's been done to solve it so far without any success:

• driveshaft balanced;
• 2 complete sets of tires balanced, rotated and swapped around etc.;
• all new u-joints;
• alignment;
• new upper and lower ball joints;
• new anti-sway bar bushings;
• new rotors/brakes/calipers;
• various seals etc.

Nothing has worked. Also, I do not see anything leaking underneath. If the pinion bearing is going bad, could it create this vibration without showing a leak?

Chasing this vibration is costing me time, money and my sanity!!!

All thoughts welcome!

 

You should have started a new thread, for sure.


This is kind of my internet rule #27. "When vibration occurs, it's always a tire, but nobody on the internet has ever heard of a vibrating tire."


Discuss amongst yourselves.

 

There are a LOT of things that can cause a vibration. To avoid confusion, I split this off into its own thread.

 

I too usually think tires when there is a vibration issue. However, I think it's safe to say we've eliminated the tires as the vibration source. I have two sets of tires mounted on separate rims. We've mixed and matched every possible combination and completely re-balanced all 8 tires twice now. This did not solve the problem which led to all of the other work being perfomred a step at a time. Still no luck.

 

So thinking about this further, does it vary with throttle input?

If it's less with a greater load you don't have a bearing problem. Almost sounds like a driveline angle issue. 2,500 lb load will squat the truck and alter your driveline angle, that can cause or resolve vibrations if something isn't right.

 

I think Tom has something you should check out. Does the truck have a lift?

 

I have been chasing a vibration issue also. I just figured it was the weight I had in the truck but it turns out my tranfer case was 1qt of tansfer case fluid low. Its much better now

 

Hi guys, no lift on the truck, stock tires. The diff and tranny fluids are clean and right where they should be. Not sure about the transfer case ... is there a separate way to check this?

You can see from the low mileage, it's a bit of a creampuff and from the overall mechanical and cosmetic condition, it appears it was not used as a work truck. The vibration is mostly affected by speed ... and somewhat by load. There is no difference whether I am feathering the throttle or sticking my toe into the skinny pedal (which I do rarely).

I usually drive with no/very light load (except for a full size Leer bed cap - guessing about 300#) and driving unloaded is when the vibration is at its worse. It occurs like clockwork between 45 mph and 50 mph. It "eases" into the seat of my pants vibration as I approach 45 mph from zero and gradually decreases vibrating as I go above 50 mph. At speeds above and below the cited range ... no vibration whatsoever. You really don't feel it in the steering wheel ... another clue it is coming from the rear?

Under load (i.e. our 2500# truck camper), it behaves the same but the overall vibration is less intense (maybe half the feeling) ... but it is definitely there. The rear end drops about 3.5 inches with the camper unit and our cargo trailer on hitch (300# tongue weight).

Since the vibration occurs in both no load and load situations, wouldn't this eliminate the driveshaft angle theory?

 

Jack the rear off the ground and you'll eliminate tires completely. You said you checked the diff oil? Any metal besides the little bit of normal sludge? If you have a bad anything you'll have some metal there, depending how bad on how much you will see. Shift the trans manually, so you are in a different gear at that speed. A bad bearing will be constant and not come and go at different speeds. It may be noisier with or without throttle. If you vibration is at a certain speed only you likely have a balance or angle issue.

 

What about when you're off the throttle completely?

 

That might be a hint. A load causes the rear to squat, which changes the drive shaft angle. That would point to U-joints being the issue, but you changed those.

Have you checked your carrier bearing (if your truck even has one)?

 

There was a recent thread (almost exact same symptoms) in the Excursion forum (I think) and the answer was a dry slip joint on the driveshaft. Lubed it up with moly greez and Viola' ! Vibration gone. Hope it's as easy as that.

 

Dry slip joint, or, what about a u-joint that's binding up?

 

I'd lean towards doing this too. If nothing else its the cheapest option available to start at first.

 

I'll give this a shot ... can't hurt. The ujoints shouold be fine as they were just replaced but I'll check those again too.