at about 80 my rear begins to vibrate on my 88gt. its got the fiero store rear control arm kit and the shocks seem ok but arent new(though, have been replaced at some time). dont know how to go about looking into it so i was wondering if there were any common problems.

axles have no(minimal) up and down play when lifted in the air or loaded on the alignment rack, there are those bearing/seal things installed on my trans.
bearings in the rear have no play at all

any ideas would be great.

If the tires have a lot of miles on them they could be out of balance. As tires wear their balance does change.
Bad tire, Check for bulges or bubbles on the sidewalls.
You could have lost a wheel weight or have a slightly bent wheel. (Did you hit any large pot holes lately?)
Ball joint possibly going bad or just very worn.

Since it is happening only at that high of speed I would look closely at the tires and wheels.

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[This message has been edited by Oreif (edited 02-01-2008).]

the 2 obvious - are wheel balancing & condition of the struts.
and - for more fun - one will wreck the other. and, there is also ball joint & tie-rod ends - but you'd have other issues with these also - klunks & pushing one way on gas, and the other way off gas.

No tie rods on 88

quote Originally posted by Robert 2: No tie rods on 88

yeah....I always forget about the 88's.....

I agree,one of your tires is out of balance or out of round (slaming on the brakes and laying rubber in the road will do this).You may have thrown a tire weight, (sometimes you will see a discoloration on the edge of the rim where the weight was).Inspect your tires for uneven wear.You might try greaseing the ball joints (if you have them on the 88?).