Ive got a 70 challenger 4 speed dana car and i drove it for the first time this year the other day when it got warm i went about three miles and it started jumping in the ass end like it had a knot on one of the tires so i changed tires and it done the same thing so i changed the u joints front and back and drove it and for about 3 miles it done fine and then it started jumping up and down again like maybe a axle bearing or something is getting hot and then starts to hop up and down in the ass end has anybody had this problem or have any suggestions any info is greatly appreciated thanks.