Driveshaft lengths- what length do I need?

Discussion in 'U-shift em' started by CJay, Jul 1, 2017.

  1. CJay

    CJay Supercar owner Staff Member

    Need some help and a refresher course on 70-72 GS driveshafts....

    This is on my "beater" GS 455. What it had in it as of 2 weeks ago was a 455 with a short tail 400 and a swapped in 71/72 style 8.5" rear. Before the driveline got removed, I noticed that there was a lot of yoke hanging out of the tail shaft. Maybe a couple of inches. It was definitely the wrong yoke as it wasn't the stubby T-400 style yoke but the longer variety. And it had a weep hole which kept making a mess under the car if it sat for a week. The driveshaft I have in there is of unknown origin.

    Now, the new driveline Im installing is the same 455 but with a 71 Muncie M21 (big output) and Im swapping in the original 1970 8.2 3.42 posi.

    My question is- what length driveshaft should be in the car with the T-400 and 8.5" And what length driveshaft do I need for my Muncie and 8.2 swap over?

    Im thinking the tail shafts wind up in the same location regardless of what transmission is installed, but has to do with the rear? I remember the 8.5 requires an inch and a half shorter shaft but Im looking for the factory lengths to determine what I have and what I should be looking for
     
  2. Bigpig455

    Bigpig455 Fastest of the slow....

    So by the service manual, the TH400/8.5 should be 54.2 from u-joint center to center. Add .2 for the M20 (54.4) and subtract.. what do we agree on .5-.75? for n 8.2/8.5 swap? I think net anything from 54.5 to 54.0 should be about right...
     
    Last edited: Jul 2, 2017
  3. CJay

    CJay Supercar owner Staff Member

    Thanks Rhett! I never thought to look in the manual for lengths. Just went out and checked what I have. Its 54" so I think Im golden.
     
  4. Bigpig455

    Bigpig455 Fastest of the slow....

    Here we go - from the 71 manual for posterity.....we can thank Ken Geis from Everyday Performance for the .jpeg.
     

    Attached Files:

    Davis likes this.

Share This Page