vibration while driving

[Anonymous]

66, mustang coupe 200 6 cyl auto,4 new tires balanced, all new front end parts uca, lca,coil springs, etc. front end lineded up at shop.rear recently rebuilt, moter idles perfect but while driving from about 20 mph on up feels like a bad vibration coming from floor . steering is smooth ,no shimmey in wheel. any suggestions on what to check. i was thinking driveshaft. thanks for any help , mike

 

[BIGREDRASA]

Get underneath and wiggle the driveshaft, to check for worn out U-joints. You don't want those breaking while you're out, specially the front one. Think polevault.

 

[Anonymous]

I agree, either u-joints bad, shaft is bent or ballance weight fell off.
Try taking it up over 20 mph on a vacant road, take it outa gear and turn of the motor, BUT don't turn the key so far the steering locks.
If it still shakes its the drive shaft.
My Ranger did this but not untill 50 mph, one bearing in the cross was compleatly shot, luckly the yokes were just fine.