tttm2 Posted July 1, 2020 Share Posted July 1, 2020 Hey guys, I’m just looking for some input, I have a 1972 Monte, modified, running a 555 ci big block, a th400 manual shift transmission, I’m having problems I think with the driveshaft, it is the original one. I changed the transmission yoke to a strange yoke that fit the th400, (and having said all that the car hasn’t run since 1993 when I took it completely apart and that driveshaft has moved 3 times to different houses) I have a massive shake at around 60 miles an hour when I accelerate hard, definitely in the drivetrain. Any ideas? And to install the current driveshaft I have to load the rear suspension in order to get it in. Quote Link to comment Share on other sites More sharing options...
tttm2 Posted July 1, 2020 Author Share Posted July 1, 2020 3 minutes ago, tttm2 said: Hey guys, I’m just looking for some input, I have a 1972 Monte, modified, running a 555 ci big block, a th400 manual shift transmission, I’m having problems I think with the driveshaft, it is the original one. I changed the transmission yoke to a strange yoke that fit the th400, (and having said all that the car hasn’t run since 1993 when I took it completely apart and that driveshaft has moved 3 times to different houses) I have a massive shake at around 60 miles an hour when I accelerate hard, definitely in the drivetrain. Any ideas? And to install the current driveshaft I have to load the rear suspension in order to get it in. And happy Canada Day!!!!🇨🇦 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted July 1, 2020 Share Posted July 1, 2020 The driveshaft length for a BBC/th400 12bolt is shorter than a th350. It should measure 54 1/2 from center of driveshaft u-joint to center of driveshaft u-joint. Just the shaft. Not to the end of the yolk. Also, the yolk should be "short" design. This is if you are using the stock style short tail th400. That being said, how is the tire balance? 60mph is usually tire balance. When you installed the strange yolk did you check the backlash on the gears again? Hope this helps. 1 Quote Link to comment Share on other sites More sharing options...
Blackhawk Posted July 2, 2020 Share Posted July 2, 2020 How are your engine and transmission mounts? Do your u-joints have any play? Was the driveshaft balanced with the new yoke? Quote Link to comment Share on other sites More sharing options...
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