Hello. I have a 70 F-100 with a 390 and a T85 overdrive 3 speed transmission. I have an issue when I let out on the clutch to take off in first gear. When I get about halfway off the clutch, there is a loud thump under the truck, almost like it slips for a second and then drives. It did it several times today for about 5 minutes and then it quit after driving it and getting it warmed up. It was very cold here today, so I don't know if that made it worse but it was worse today than it has been before. I can feel the gas pedal move some too when it happens. It almost reminds me of a broken motor mount but I don't think it is as they are fairly new mounts. Plus the fact that it quit after warming up. Just wanted to see if there was any thoughts on the subject. Thanks

Dan

 

sounds like bad motor and/or transmission mounts .
gas pedal moving is a tell tale sign !

 

That's exactly what I thought but I put the jack under everything yesterday and didn't see anything separating. I don't know, maybe I didn't jack it up enough. Plus the clutch shudders pretty bad sometimes when it's cold and wondered if that broke a mount.

 

Have you checked the U-joints??

Crawl under the truck and grab the drive shaft,... twist it.... does it twist?

Grab drive shaft at each u-joint ,...one at a time. push it fore and afet, left and right against the cross of the joint ,... if it moves,... replace joint.