hi sages- never been up against these exact symptoms in 50 years of wrenching. when car is warmed up and have traveled at least 15 miles @ 50 mph , i get a chattering and shaking when i release the clutch in 1st gear(m 47). at all other times clutch releases smoothly if on trips of less than 15miles. next day when car is cooled off - no problems. clutch is not slipping. wish these cars had a bolt on inspection cover on the bottom of the bell housing to easily inspect the clutch, like many american rwd tanks. anyway had two theories- 1st universal joints on front and rear of driveshaft are shot-did the rock up and down and left to right test on them and there is no movement. 2d checked engine mounts and mounts on transmission- no movement, cracks or deteriorated rubber noticed. uncle moe said check the lubricant in the trans and differential. doubt this could be the problem since there is no trans or rear gear noise or hard shifting. if the mounts were bad or a u joint was shot, wouldnt this symptom be fairly constant? have replaced u joints usually to cure this problem or occassionally shot mounts but this was on american tanks(dodge, ford). dealer said it was the clutch disc not releasing on the input shaft spline which his clutch job for only $2000 would take care of. moe said he was full of kweet. sounds like the cleaners to you? thanks tons for your guidance oldduke