Sometimes when Im driving 50-80mph my car will shake violently (like driving over the shoulder bumps on some highways used to get your attention). Once the shaking starts, it gets worse when I give it more gas but goes away if I let off the gas and then accelerate again. This does't happen all the time either. Could it be a faulty gear transition? I have a automatic tranny. I have also noticed it does't happen when Im cruising but only when I accelerate when Im already cruising at 50mph+.

 

Have you had an alignment done recently? It could also be your drive shaft-it doesn't have to be out much to cause problems.

 

I had the same problem when I first bought my car. Had to change every single piece of my front end suspension. Tie rods, ball joints,adjusting sleeves, gas struts, strut cartridge, shocks, lower control arms, idler arms, sway bar, computerized wheel alignment and all bushings. Also had new brakes not rebuilt and wheels and tires. Now I can let my steering wheel go at 100 miles per hour and she runs straight as an arrow for at least a half mile. Remember these cars are made for handling so if the handling is screwed up then the car is no fun to drive. Besides that when your car is shaking like that wonder what else it is messing up.

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86 Camaro Black SS Coupe, T Tops, Flowmaster, Custom Paint, Dunlop Road Kings S/R tires, Wheel Country Directional Chrome Wheels,new charcoal & gray interior including seats and door panels, new carpet and headliner, complete front end suspension rebuild, new Valve seals, and more mods to come
http://www.angelfire.com/sports/niterider/86camaro.html
Morgan_Andre@hotmail.com

 

It could very well be as simple as your tires needing to be balanced, or broken belt in the tire or tires etc. I will tell you what happened to me, I bought new valve stem caps for my car (Skulls) they were heavy. It said on the package when I bought them, that they may cause the tires to be off balance. Well sure enough, between 60-70 MPH the car vibrated in the front pretty bad. I automatically thought I had some big front end problems. So I removed the caps, and put the regular little black plastic ones back on, and no more problem. So it might be simple. Good luck man.
Take care
Mike

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Maybe Ill get my wheels alinged. Like I said, this doesn't happen all the time. Even at high speeds it only happens on a few occasions. Still I will get my wheels balanced and tires algined. BTW, what is involed in balancing and aligning?

 

As HUMMER suggested sounds like maybe a bad U-JOINT.I would check this first since it wouldn't cost any thing.Balaning is simply where they put the tire on a tire machine that spins it up to speed and detects any vibration and then shows the man where it needs weight to counter to vib.Simply put.Alignment they hook up four for pieces of equipment(don't know exact name) to your tire on a four wheel algin.Again there is a machine to read if your tires are pionting where they should be.There are three settings Caster,Camber,Toe.There's a specific setting for all cars and they would set it to specs.Someone else may beable to make it a little clearer but should give you an idea.

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1991 1LE Z28 355cu 5SPD (ORIGINALLY 305 BEST E.T. 14.186@99.86mph)NO PASSES ON 355 YET.MINI RAM INTAKE,AFR 190 HEADS,10.23:1cr 24# SVO INJECTORS,BBK 52mmTB,AFPR
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Sounds to me like the torque convertor clutch is chattering as it tries to unlock when you try to accelerate in cruise at 50 to 80 mph, it will stay locked at low throttle settings but they unlock to give you better acceleration when you give more throttle, my 93 chev truck only does this with a heavy load going up hill at about 80 mph so i havent worried about it, if yours is bad at lower speeds and loads you may want to ask one of the trans experts on the transmission board here about it. Good luck, Dave