have a question regarding the turbo 400 slip yoke i need for my driveshaft. i have a turbo 400 out of a 70 pontiac in my 80 olds cutlass ,it has a 4.25 tailshaft housing on it .the shop building my driveshaft whats me to come down and get a couple different length yokes and bring them home ,slide them in the housing to see which one fits best .he said depending on the length of the yoke some could interfere with the speedo gear (which is about 5.5 inches back from the output shaft seal).i could do this but would require several one hour round trips to the shop i would like to avoid.with the suspension loaded it is 54.75 inches from the center of the rear joint to the rear output shaft seal (the measurement the shop asked for)seems there would be an easier way to determine the proper yoke length.thank you

 

With the 4.25 tailshaft housing you need the short slip yoke.

 

Was the core trans they are building a short shaft originally? If they are converting a long shaft to s short shaft, and using a output shaft with threads for a bolt on yoke, you may have interference. The Bolt on style shafts have a o-ring that requires a yoke with a counterbore, the splines don’t go all the way to the end. If you use a yoke without the counterbore (internal splines all the way to the end) the splines will bottom out on the machined groove for the o-ring. If that’s the case, you have 3choices: #1, get the right output shaft. #2, machine the yoke for a counterbore to clear the o-ring, or #3, grond or machine the o-ring groove from the output shaft.

The older short shafts are getting a little harder to find. The bolt on yoke style shafts are still pretty common. I don’t have the equipment to add the counterbore to a yoke, but I do have access to a lathe. I have also used a hand grinder to remove the o-ring groove from a fully assembled transmission.

If you need pictures to describe what I’m discussing, I can post some pics tomorrow.