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Discussion Starter #1
hey
im just curious to know why my mustang vibrates when it gets to 80 and higher, ive had my tires rotated and balenced and alligned, ive put good gas in it, ive put on a new airfilter, and the engine was just rebuilt last september, its a brand new rebuilt motor, and im wondering why its vibrating real bad when gets up to 80 and higher, im not an expert at cars, i just know the basic stuff, and i was just inquiring to see if any of you guys could help me out and give me some answers, thanks if you can help me out and tell me why its doing this, would some stp octane booster hurt my car if i put some in there? see i dont know much about cars so help me out here, oh yea i have a inline 6 200 cubic inch engine, 1 barrel carberator
Dan
 
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Discussion Starter #2
Could be the drive shaft is either bent or out of balance.
Or maybe just a bad U joint.
 
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what can i do to correct or stop it from vibrating? i would tell my dad, but he would get pissed at me for driving it that fast, so what can i do? what about the ocatane booster? would it hurt my engine?
 

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I had a similar situation on my wife's Sable - between 60 and 80 there was an auful vibration. Got the tires rotated and balanced and still the vibration. I decided to take the car to a high-end front end shop (they do trucks, hotrods and such) thinking maybe the wheel was bent. They "speed" balanced the tires to 120 mph. No more vibration. The guy said that normal balancing is done at about 50 mph.

The speed balancing is done on the car, so you actually get the entire hub assembly balanced on the car. Downside... if you take a wheel off the car, it has to be replace in the exact same spot - lugs and all. You may want to look into.
 
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Discussion Starter #5
Several things can be wrong. I had this trouble in my fastback, and it was annoying.

1.) Out of round wheel. No balancing in the world will fix that, you need to replace the wheel.

2.) Bent driveshaft. Replacement is the only real answer.

3.) Bad U-Joints. Easily replaced with a quality set.

4.) Bad output shaft bearings or shaft from transmission. Only real solution is to rebuild the transmission professionally and replace both if required. (This was my trouble along with a slightly out of round wheel.)

5.) If you have a stick, your flywheel may be out of balance. Easily fixed by replacing same, or try a good machine shop.

6.) If you have a stick, your clutch assembly could be defective and out of balance. Replace with a quality replacement.

Octane booster will not help this problem, don't waste your money.
 

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When you wheels were balanced did they use the large center hole or did they use an adapter into the lug nut holes. My experience back when these cars were new that the big hole is not in the center of the wheel assembly.
 
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Discussion Starter #7
In addition to what's been suggested, check motor and tranny mounts, especially tranny mount.
 

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I had this problem with my '69. Changing the tranny insulator ($9.00 at autozone) fixed the problem. I could not believe it.
 
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Discussion Starter #10
Yep, tranny mount insulator... made an amazing difference! Good luck.
P.S. I also checked my U-Joints and they weren't great... not a bad idea to replace them if you don't know when they were done.
 
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