My car is a 1970 396 SS with a TH400 trans. When I shift from park or neutral into drive or reverse there is a lound banging noise in the driveline regardless if my foot is on the brake or not. Could there be a problem in the transmission converter or in the transmission itself ? I ask this question because:

1. The drive shaft has new universal joints, transmission slip yoke, differential pinion yoke and it has been balanced.

2. The differential has been completely rebuilt from pinion to ring gear, all new bearings, seals and both axles. This was a precision rebuild.

3. The car idles steady in park at 600 RPM.

It seems to me that all that is left is the transmission and converter to look at in this dilemma. I can not be sure if the converter or trans are pure stock. As such I do not know what stall spedd the converter might have. When I first got the car, I thought that the rear end might have a hight gear as the shifts seemed to be close together and snug. But when I got into the rear end, I discovered that the gear ratio was 2:73. So there it is..........any suggestions or cures for the banging and lurching???

Russell

I had a problem similar to that with our '76 Chev Truck. It had a very healthy 355 and a TH-350 trans that would bounce your head off the back window if you were not ready when it shifted. One day I got in to head to the local cruise spot. I put it in reverse and I heard a very distinctive 'clunk'. Turns out the flexplate had cracked in a complete circle around where it bolted to the crankshaft. This may not be easily seen with the motor/trans in the car. But it is just an idea for you to check out. I have pictures of the flexplate after I pulled it out. Kinda scary knowing the night before I was making regular 6,000rpm shifts.

Charles

Hey Charles..........that flex plate sounds scary and I am going to do my best to check that out. I am sure that my car has had many owners and experiences so everything is up for grabs. I also got a private message relative to excessive line pressure in the trans that can cause this situation. If the intake manifold vacuum, going to the vacuum modulator on the trans is insufficient, it can cause the modulator to operate in a manner that places more line pressure in the transmission, hence it causes it to engage hard. Remembering of course that the vacuum is highest at idle and drops off as the speed of the engine increases. If there is not enough vacuum at idle this situation can arise when dropping the trans into gear. How about that!! This of course is if everything is for the most part stock, such as the stall speed on the converter and the guts of the trans. Before I go any further, I am going to check the vacuum to the modulator and the line pressure in the trans. The vacuum should be about 15-18 inches at idle and the line pressure 90-100 lbs at idle.

Thank you Charles for your information about the flexplate. If any one can add to any of this information, help me out. I am going to try and check this out before monday as my wife Linda is dragging me out of town for two weeks. I'll let you know how I am doing...........Russell