Pontiac Repair: Pontiac Trans sport SE 91, pontiac trans sport, automatic gearbox

Question
My 3,1 automatic trans sport starts shaking with low frequense when the look up gets engaged around 25 km/h. Also around 50 km/h it shakes heavily. If i speed up it dissaperas more or less. Tires and weels are perfectly balanced. Could it be the drive shafts or is it the automatic gearbox end gear?
A wonderful car !
all the best
Sten

Answer
Hey Sten:

It could be either or both of them. You could have a bad CV joint or Tripod joint. You could have an internal transmission issue. The lock up you talking about usually is way after 25 MPH it's usually in the range of 35-40 when the transmission reaches 3'rd gear. You can do this there is a an electrical plug on the side of the transmission it's actually in the front of the van it has either 3 or 4 wires on it gently unplug it the plastic will be brittle and drive it to see if the problem is gone. If so then it an issue with the transmission torque converter lock up. if not then you have to look at other transmission issues. How's the fluid low burnt?? other factors you could have an issue with a motor or transmission mount that loose or broken causing the vibration when the engine toques forward and backwards. Back to the drive shaft issue if you make a sharp turn to either side doe it make a grinding/popping crunching noise? That would be a tell tail of a cv joint issue. Take a look at the boots to see if they are leaking grease out or they are ripped off altogether.. Without driving this and actually feeling it it's really really hard to tell you what's wrong. Good luck...