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Discussion Starter #1
I have a 68 coupe with a 289 and c4. I was on the freeway last night and as i approached 70 mph the car would start to shake if i put my foot into it. but when i let off the gas it would stop. at 60 this wouldnt happen. if i was coasting at 70 there was no shaking. also off the freeway at about 35-40mph, right after i shift into 3rd, if i barely put my foot in it enough to keep the same speed there is a shaking that i can feel in the shifter and the pedal which i am pretty sure is the engine. can someone help me out here?

1968 Mustang Coupe - Daily driver
289, holley 600 carb, holley street dominator intake, petronix ignition, Accel Super Stock Coil, Tri-Y Headers, 2 1/4" 2 chamber Flowmasters, C4 and 2.79 rearend
 
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Did you have it out of gear when you were coasting at 70? If so, I would suspect a driveline problem. It might need to be balanced and checked for trueness.
 
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The first and easiest thing to check would be th u-joints, but under power only suggests maybe the rear thrust bearing.

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"Sometimes a man's life can depend on a mere scrap of information."-The man with no name
 
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Discussion Starter #4
make sure your wheels are balanced and also if they are maybe a wheel weight fell off.
 
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