They are the same length BUT be aware there are 2 different styles of u joints, inside snap ring or outside snap ring. That means the driveshafts won't interchange unless the matching yoke on the differential is used.
And also of course a TH400 uses a different yoke in the back of the trans vs. Powerglide or manual transmissions.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
Will the front yoke slide all the way into the trans and bottom out?
I had one years ago that I fought and fought with. Finally figured out the splines actually had a twist in them quite a distance into the yoke and that was the issue. It wouldn't bottom out in the tailhousing on the trans.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
Take your car and put it into a hoist with the rear differential hanging freely
Next, place the tail shaft into the transmission without a U joint in it
Next measure depth to ensure it will bottom out, once verified, pull the tail shaft out of transmission 3/4 to 1 inch, and leave it there, markit with masking tape or something like that.
Next measure the distance between the center of where the U joint caps would be , You have to visualize the center points both on the tail shaft and the differential. Would help if you had a buddy to help with this.
Once you have this measurement, mark it down , then check to make sure the tail shaft is still 3/4 to 1 " from bottoming out into the transmission.
Next comes the hard part, you have to lower the car and put the weight of the car on the rear differential and front end.
Well , if you successfully did lower the car and put it's weight on the differential and front end, repeat the measurements taken from the center of the U joint cups.
From my history, there should be about 1/2" to 3/4 " less , if this is the case , what I have done on projects is I push the tail shaft into the back of the transmission about 1/4" to allow 3/4" to reach bottom , then remeasure from center of cups to find your true length of the drive shaft.
This process has worked for me on a few occasions, it make not be the only or for that matter the correct way, but it worked
Good luck ,
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New Brunswick , 1950 Pontiac Silver Streak 2 Dr Sedan, 1967 Beaumont, 1985 Sierra 1500 One Owner
