weird vibration at high speed?

Hello all. I was driving my New(new to me) 95 blazer today, when it started vibrating, not only did it vibrate, it had a weird bassey sound to it. I though i had gone on to a new pavement and not noticed it, but if i gave it more(or less) RPMS it didnt do it anymore.

What could it be?

Thanks

2WD or 4WD? What speed is it noticeable?

4WD

umm it starts in maybe third gear(anywhere from 55-75 MPH)

edit

and its always when i try to slowly gain speed
it will hit a certain RPM(always varies) and then do it.

U-joint on the rear drive shaft is where I would start. and if one is bad, change them both

How much do those cost?

My cousin is a Mechanic, i could have him take a look.

And if its not that?

http://www.autopartswarehouse.com/details/QQChevroletQQBlazerQQMoogQQBall_JointQQ19951996QQM OK5289.html

edit

is that it ^^^^?

anyone?

No, that is a ball joint. There is a universal joint on each end of the rear drive shaft. Usually less than $20 each.

if you have a relitive that is a mechanic that can look at it, do so.
the u-joint is just a start but of course with any type of problem there are simularities to a point.
As for cost, u-joints are about 20 ea. plus instalation of whatever the going rate where you live. Again, have your mechanic look at it and give you a deffinate answer. You could even just check your tire pressure for starters, some vibrations can be caused by that as well.
out of ballance tires, bad front end parts,U-joints stabilizer bushings/sway bar bushings or even a bad tire.

He's going to look at it. He said it could just be the tires

So we'll see what happens

Thanks

Had my cousin look at it. He just told me that if it were the U joints, that it would probably be heard whenever in motion, not just in a high gear. He told me its probably my alignment, and when i get new tires(soon) to tell them to realign the wheels....

In the early stages of U joint wear, the vibration is only noticeable at either 35MPH or 70MPH depending on which joint is worn, (front or rear). U joint vibration or sound will decrease on decelleration and increase on acceleration but usually remains within a few MPH of the those speeds. It's possible that the wheel alignment is out of specs, or there are worn parts which can both cause tire wear, but, tire noise is usually heard/felt starting about 20 MPH and increases with speed. Tire induced vibration usually starts around 45MPH and also increases in intensity as speed increases. From your description of the symptoms, check the U joints first.

Hahah
Thanks man. my cousin is just becoming certified. So he needs some experience.

Thanks alot. What should i do about them? Are they dirt cheap? Easy to install? I dont want to go up there to have him do it....(nor do i want to pay outof the ass to get it fixed lol)

If they're worn, they need to be replaced so that other parts are not damaged needlessly. U joints usually are under $20 each, they're not difficult to replace, IF you know what you're doing ;) Some auto parts stores have machine shops. If you remove the driveshaft and bring it to them, they'll replace the joint(s) for you. That way you'll at least save the labor cost to R&R the driveshaft.

How much would a shop charge to do it. Just me taking my car in and barking out orders at them lol

Depending on the labor rate in your area, flat rate is around 1.3 hours for one joint, and 1.7 hours to replace both joints, plus the cost of the joint(s). Call around for an estimate, they'll tell you within a few bucks how much it would be.

Seems like you're novice to this? If you decide to take the shaft off as old master suggests, make sure that you mark the shaft and the rear end so that it gets reinstalled the same way it was removed. Last time I checked, joints and installation with shaft removed was just under $100 where I live.