My '98 2500 4x4 has developed a vibration underneath that happens above about 60 MPH. It's not a tire balance kind of vibration, but a kind of humming grinding feeling that I can feel through the floor and a little bit through the pedals. It kind of feels like it would if one of the front tires were a super-aggressive off-road tread or something--just a humming feeling. I thought perhaps it was the 4x4 disengaging incompletely, so I moved the lever and it seemed to make it a little better.

It happens at very light throttle, just above coasting on the highway. I know it's not the transmission, because it happens at the same speed, OD on or off. Would U-joints be a slight, high-frequency humming vibration? Could it be the transfer case, maybe if it were low on fluid (it drips a little, but certainly not enough to drain it). What does a U-joint feel like when it's going bad?

The crappy thing is that it wasn't doing this three weeks ago before it went to the dealer for a totally unrelated problem. Although they did replace the rear brake lines...

Any thoughts?

 

wheel bearings? or a ujoint

 

I thought wheel bearing but the only way I know to check one is to swerve from side to side to see if the noise changes. He said it does it at 60+ mph.......and that might be dangerous.

 

What about the automatic hub locks? I am finding lately that when I go around tight corners, my tires chirp as if it's not fully disengaged from 4WD. It looks like the locks are merely vacuum operated--that doesn't seem like the most robust system. Do these things have problems in that department? It would probably explain why it came on after a trip to the dealer--during the tow, the driver put the transfer case in neutral. Right after that, I started noticing the vibration. How do I know it's fully disengaged?

Thanks!

 

is your 4wd light still on. if your getting a vib on the hiway like that. the first thing i would do is have a buddy stand next to you truck and see if the front driveshaft is turning when your driving past him. if it is and your 4wd light isnt on the the t case might be stuck in 4wd still. ive left it 4wd with my front axle disengaged and it will make the same kind of vibration at hiway speed. around town i coulnt tell. other then that it could be your rear shafts u joints or a few other things

 

No, the 4WD light is off. I even went to a parking lot, put in in 4WD (lo and hi), then neutral, then back to 2WD and backed up. No problems, except the damned vibration. I can definitely feel it most through the steering wheel, so I gotta believe it's in the front end somewhere. I'll have someone stand next to the truck and see if the shaft is turning. If it is, then what?