I do believe my torque convertor has gone bad on my 68 turbo 400. I am getting vibrations when I get the speed up to 40mph. I thought at first it might be the ujoints, but I took the drive shaft to a drive shaft guy here in Houston and he said the drive shaft was bad and needed a new one. He made me a new one and of course the vibration is still there. I did not think the shaft was bad because I could not feel the vibrations coming from the rear which has a 308 in it.

I jack the car up and put jack stands on all 4 corners. I started the car and speed up the engine to about 2000 rpm and I was getting vibrations even without putting it in gear. Next step I then disconnected the convertor and pushed it backwards into the transmission. Started the car again without the convertor being connect and the vibration was gone which lead me to believe the convertor might be bad. Also before I recall that once I would put the car in reverse it would make a sound like the engine was idle to high which it is not. The transmission has no problem at all changing gears so that is why I am leaning to a bad convertor which I think they very seldom go bad but I do believe this one is. Ok my question is which is a good torque convertor to buy. My engine is a stock 455.

Gary

 

Before replacing the converter, you might try reclocking it.

Reinstall the converter bolts, start the engine and try to duplicate the vibration. If it’s gone, put a paint mark on the converter and flexplate. If you ever need to remove the transmission, be sure to reinstall the converter in the same spot.

Still vibrates? Remove all the bolts, turn the converter 120* and reinstall the bolts. Start the engine and check for a vibration. Still there? Turn the converter another 120* ( make sure you turn it the same direction, and not put it back in the original location!) and try again. You might get lucky.

 

Thanks for the reply Matt

I am fairly certain that convertor is bad especially after I separated the convertor from the flex plate. Once i did that and started the car the noise I was hearing and feeling went away.. Once I bolted the convertor back on the vibration came back and I did not even put the transmission in drive. So I ended up pulling the trans and ordered a new Hughes Convertor from Summitt. Before I ordered the convertor I called Hughes tech support and they also thought my convertor had gone bad and suggested I get either their GM4FUEL or GM4xtm-1.. I had to also give them the specs on the cam in the car to match the specs to the convertor. I would be the first to tell ya that I never knew the size of the cam needs to be included in the equation when selecting a torque convertor.

I ended up ordering the Gm4xtm-1 from Summitt because it was rated at about 2000 stall versus the GMfFUEL which had about 1200 rating stall. But the tech whose name was Kevin at Hughes said either one should be fine with my application and either one would match my bolt pattern.

 

Hughes builds nice stuff.

Before installing the converter, drop the trans pan. Make sure the old converter wasn’t tearing itself apart. If you find a bunch of metal in the pan, plan on having the transmission inspected. Whatever crud and debris that’s on the existing fluid and trans will get pumped into your new converter and contaminate it.