81 SX4 vibration at around 75mph....Solved!!!

[shanebo]

Hey guys I just had a quick question about a vibration my new 81 sx4 4 spd, full time 4x4.  It runs a drives great up to about 70. at 70 it starts getting a vibration that i would compare to driving on a washboard road or a real gnarley rumble strip the dash really shakes but and its pretty loud yet it really doesnt seem to shake the whole car...it still handles ok if that makes sense. Pigonawing has a similar post but mine seems a little different. once you cross the 70 mph mark the vibration gets worse the faster you go...under 70 mph it rides like a cadillac...I was wondering if I put the car up on jackstands and ran it up to 75 if I could get it to reproduce that vibration.

[WoodenBirdOfPrey]

I'd be pretty cautious about putting it on stands and running it fast.  If it's because something in the drive line or a wheel/tire is out of balance it could end up being a lot worse without any load on it.  With that, there's a chance of it shaking off the stands and chaos will ensue.

Have you checked the wheel bearings?  I had a work van that was like that, at slow speeds it was fine, but at highway speeds it would start humming/vibrating almost exactly like the sound of rumble strips.  As the bearings got worse and worse, it started happening at pretty much any speed over 15 or 20 and would be so loud it was difficult to talk to the person sitting 3 feet away.  In that case it was the front passenger side wheel bearing, and the only time it would get quiet was when I turned one direction (I think it was when I went left) it would get quiet momentarily like nothing was wrong.  Also going over a sharp hill where the van sort of floated up off the suspension it would get quiet for that split second as the weight lifted off the bad bearing.

[shanebo]

Heres a shot of the rear end...it looks pretty wet, do ya suppose somthing in the rear end is causing this? Ive had rear ends go out before and the made a growling sound...this is totally silent, until you hit 70 that is....

[shaggimo]

After a frontend shake down, if nothing seems obvious, look towards your tires. How old are they? When was the last time balanced? I have had tires on my car that were perfectly smooth up to a specific mph, then they would rattle your teeth loose. I balanced the tires, no more shake. I have to re balance my jeep tires a couple times a year for this issue as well.

[eaglefreek]

I agree that I would start with a tire balance and work your way form there. Try to find someone that uses a Road force machine and hopefully they know how to use it correctly. Tire shops want you in and out. They don't charge a whole lot to balance tires so they aren't going to spend a lot of time on your tires. The little experience I have with tire balancing was when I was in high school auto mechanics class. I would take the time to break the bead of a tire and spin it accordingly until I got it close to zero without weight. However the teacher would show us with an on the car balancer, how a balanced tire may still not be right once on the car.
Here's a interesting read regarding Road Force balancing. http://www.tundrasolutions.com/forums/tires-and-wheels/96268-road-force-balancing-what-questions-ask/

[recomer]

I have a vibration on mine when I get above 60 and it settles down around 70. I'm thinking tire balancing as about 8000 miles have been put on it since we got it and haven't rotated the tires. Going to try and get them rotated/balanced this week to see if this sorts mine out

[captspillane]

If it comes and goes as you accelerate, replace the steering stabilizer first. If it comes and gets worse directly as you increase speed, it has nothing to do with the steering stabilizer. Eagles are prone to a resonance issue and that stabilizer is more important in an Eagle than any other car.

[ozarkrebel]

BE SAFE!!!!!  When you have a vibration the safest thing to do is check out all parts, especially when it comes to your steering components. Even if you find one part is bad (ball joint, tie rod end, steering stabilizer, etc.) go ahead and check the other parts as well, you may just find other parts are wore just as bad, which is usually the case. Replacing one part to see if the vibration goes away and ignoring the rest is just plain ignorance. You are gambling not only on your own safety, but you passengers and everybody else who happens to be in your path when a steering part lets go.

[shanebo]

It seems to do it regardless of accleration....Its that 70mph mark that seems to be where it starts...Im going to jack it up in the garage and give ita good looking over and see if I can find any worn parts.

[craigp29690]

I agree with tire balancing as the first place to look.  Then I'd look to rod ends, pitman arm and ball joints keep going from there. 

[shanebo]

I got all up under it today and the u-joints look good. The tires are very evenly worn...Some of the bushings are a little dry rotted but nothing alarming...however a replacement in the near future would be a good Idea. The pitman arm looks pretty good...almost like it has been replaced in the past few years...Tire balance is the first on my list...then I can work from there

[Eagle1984]

Mine does the same thing. Though it seems to be coming from the back only. Has gotten a little better since replacing the back shocks, not it is more around 75-80mph when it does it.

[shanebo]

Come to think of it the back shocks look pretty worn out....I bought a new set for the front, I should probably quit being so cheap and replace the rear ones too. Ill try anything at this point....thanks for the input ill pick up a set this weekend, even if its not it....it sure can't hurt anything.

[Rucuss]

I'm currently having a simaler issue in my wagon when I hit 40mph it vibrates mostly from the rear then nothing till 70mph and only when in gear. Just ordered new u-joints so I'm going to start there.

[shanebo]

Im curious to see what you find out with that. I poked around and did the jiggle the drive shaft test but didnt find anything conclusive. Please keep me posted as to your findings. If it fixes yours ill change em in a heart beat..by the way, is yours a stick or an automatic?