hey I have a question. I have a 302, t-5 and an 8' rear. When I'm goin 70-75+ mph, I get some heavy vibration. I was thinkin maybe its pinion angle or (since I have different size tires front and rear with directional tires) I might need to get them balanced (its been 2 years now since I put em on). Is this a problem or are our mustangs just not supposed to go this fast? thanks in advance for the help
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check put the u joints

 

I had the same problem. Turns out it was a tire out of round. Yes it was a Goodyear Eagle F1 ZR. These things are like a couple of hundred dollars each so out of round was the last thing I thought would be wrong (115 lbs over the 26 lb limit). I would have them road forced and this will tell. Heres a chart that may help. Also check the U joints and drive shaft.
http://www.armorb.procarcare.com/inc...04/4fig15.html