Vibration - where to look

[nicksr]

I was visiting my son at the Air Force Academy this past weekend. Last year I took him our 93 LC which now has about 260,000 miles on it.

While driving with him and my wife, I was sitting in the back seat and felt a very strong vibration. Definately not as noticable while sitting in the driver seat. he says it started "a little while ago".

Anyway, the vibration comes on at around 50-60mph and then subsides somewhat at about 70mph. However, at pretty much any speed above 50 if you take your foot off the gas, if the vibration wasn't present, it comes on strong as soon as you remove the gas.

What should I have him get checked out?

Thanks for any help.

 

[Ebag333]

U-joints been lubed or serviced lately? They're often the cause of vibes, they wear and start giving vibes, especially when low on lubrication.

 

[nicksr]

There were lubed approx. 5,000 miles ago. Of course, I didn't do it myself. So I am just going by what he requested they do and what they say they did.

How many miles are u-joints generally good for before they need to be replaced?

 

[Ebag333]

There were lubed approx. 5,000 miles ago. Of course, I didn't do it myself. So I am just going by what he requested they do and what they say they did.

That's probably not enough. Mine start complaining about every 3k miles.

How many miles are u-joints generally good for before they need to be replaced?

A long time, and they'll complain for a long time before they go out. I'm sure the u-Joints on mine are original (150k miles), and I'm sure people have gone well over 200k with original u-joints.

Lubing them properly will extend their life. Since that's easy and cheap, I'd start there and then start moving on to other things. I'd also check all your bolts and nuts while you're under there, make sure they're nice and tight.

 

[landtank]

the speeds sounds like a tire out of balance

 

[nicksr]

One can only hope it is something as simple as an unbalanced tire or u-joint that needs lubing.

Any other thoughts? Rear-end, tranny or transfer case?

it is seriously more noticable sitting in the back than the front. Which is probably why he thought it was no big deal. Of course, at 21 he thinks everything is no big deal.

One more year and then I get the truck back. I put too much money into this truck to let it just fall to pieces now.

 

[blzrfn]

the speeds sounds like a tire out of balance

Ditto! I had a nagging vibration around 60 mph and drove all the way to Miles City, MT (about 1000 miles) dealing with it. Got my tires balanced and rotated at one of my two options in town and the ride home was a lot smoother. Lube your DS, UJ, and get your tires rotated and balanced and see if there is any difference. Worst case scenario you are out under a bill and you have eliminated three potential causes.

 

[greentruck]

And a tire becoming out of balance often is because of a missing wheel weight.

Not always possible to see where something that's no longer there was in the first place, especially if it was some time ago. Sometimes you can see where it was clamped though.

 

[nicksr]

Turned out not to be the tires being out of balance. Instead, it was the front drive shaft needing to be rebuilt. Everything is humming right along now. At least it wasn't something major.