for some reason, my 2wd coupe has vibration above 70 mph and just doesnt want to stay on the road sometimes... what can cause this?

A few things can cause vibration on higher speeds...

 

First off, an out of balanced wheel, a bent rim, a CV axle with a lot of play (lateral, not longitudinal), a worn tie rod end, a blown strut causing vertical vibration from the uneveness of the road....

 

You need to be more specific. Does it do it all the time, just between certain speeds, what have you done to try and correct this? I'd go get the wheels balanced first and foremost, then go from there.

Try rotating the tires, see if it changes anything. Then go from there on checking the rest of the suspension.

Try rotating the tires, see if it changes anything. Then go from there on checking the rest of the suspension.

+1, and same for caboobaroo's comment.

 

Tie rod ends, ball joints, steering rack bushings, and even strut bearings (the rubber bits at the top) can all contribute to this problem, but its most commonly a wheel and tire issue. Knowing you, the wheels and tires are PROBABLY not the problem (I am pretty sure he has mentioned this to me in the past, and I KNOW he has gone through tires in the time we've talked)

 

The HTKYSA has a great walkthrough on inspection your steering and front suspension, one bit at a time. If you are relatively certain the wheels and tires have nothing to do with it, and you feel like throwing a little money at it, buy new tie rod ends and new ball joints, and change them. Its probably time, even though shes only got 100K she IS 20 years old, and so is the grease in those joints.

 

You MIGHT wanna check the steering rack bushings before just replacing those bits; jack the car up, put it on stands, lock the steering wheel, and try pushing and pulling each wheel with all your might, while watching the steering rack where it is bolted to the cross member. If it moves at all relative to the chassis of the car, then your bushings could use replacement.

 

In all honesty, the best chance is that its a little bit of all of the above... but the only way to tell is to tear a little further in.

i just had a tire on my 84 gl that would only vibrate at 50 mph, the strut was blown, the tire was a little out of round, weird, after you got up to 60 or so it would quit.

My axle nuts were loose. Guess I forgot the "second re-torque" I've always had to do on axles for some reason.

 

Thank goodness for the simple fixes, aye?

 

Now to go fix the other problems