"Old Smokey" needs TLC
 

I have a 79 300td that upon acceleration feels like the tire is out of round in an extreme way.Goes away when I get to 20mph or a little less. I first thought it might be the caliper or a bad cv. It is on the right rearside.This car has been sitting for quite some time. I have cleaned the fuel system and put another glow plug relay and started when cold for a while. So, in the midst of pulling the glow plugs the number one broke leaving the sleeve and element inside. I am now wondering why I am wasting my time with a car I paid $100 for but, since I put new tires on it and love the w123 style I would like to get "Old Smokey" on the road again.

i would
 

check the half shafts. park the car in a way that removes all drivetrain tension from the half shafts: set park brake and put tranny in neutral. then grab halfshafts and try to wiggle. they should not wiggle at all. if they do then that is a problem. could be causeing your humpa humpa sound.

tom w

btw be careful with the glow plug. you dont want that falling into the engine. you could bend a rod or hole a piston.