Hey Guys, I am replacing the old worn out (non orginal 8.2) in my 72. I was talking to another guy about swapping in the Chevy 12 bolt out of a '70 Chevelle. He said that I may need a longer drive shaft due to the shorter nose of the 12 bolt diff. Is this true? I have never head this before. Just want to find out for sure so I know before I install the rear diff. If it is shorter does anyone make a longer front drive shaft yoke or does the drive shaft have to be lengthend? He said the 12 bolt is about 1"-1.5" shorter. Any input???????? o No: Thanks, Mike
Should be the same length when the 12 bolt goes in. IF the rear in your '72 was original 8.5 & you were going to a 12 bolt Chevy rear, yes you would need a longer driveshaft. Seeing this more & more :spank: If some has built your 12 bolt Chevy rear with a 3R yoke from an 8.5 rear, it will mess up the above measuring. The 8.5 3R yokes are longer & when installed on a 12 bolt pinion, will require a shorter driveshaft than if a factory 12 bolt yoke had been used. :3gears: Roger
Thanks Roger, The current rear diff is an 8.2 out of a '68 Chevelle. This was in the car when I bought it 10 years ago. I believe all the '72 and later cars came with the 8.5" 10 bolt but not 100%. Don't want to sound stupid but you said if the car came with an 8.5" and a Chevy 12 bolt is swapped in I would have to lengthen the driveshaft. So could I use the longer rear yoke off of a 8.5" 10 bolt on the 12 bolt pinion and not have to lengthen the driveshaft???? :grin: Thanks, Mike
Mike, I have done this swap several times with original 12 Chevy rears. I don't have a d-shaft measurement for you because the cars did not have a d-shaft when I got them. I can tell you that when going to the 12 bolt, you will need to change the rear u-joint to a NEAPCO 3-3130 if you keep the stock 12 bolt yoke.
Mike, Hello. How long a drivshaft you need will depend on the yoke used on the 12 bolt. If it is stock 12 bolt Chevelle rear with Spicer 1310 yoke, or stock "Canadian" or "Pontiac" 12 bolt with the 3R yoke, your current driveshaft should fit, though you may need the adapter u-joint George mentioned. Touched on the 8.5 3R yoke subject, as they are longer & stick out the front of the rear further on a 12bolt. They will not take up the extra length on an original 8.5 A-body driveshaft. Some budget builders are now using the 3R 8.5 yokes on 12 bolts to get to larger diam u-joint, w/o buying a new $100+ yoke from aftermarket (Randy's or Toms). Have never liked the 8.5 yoke route on a 12 bolt as I like to be able to interchange with stock 3R yoked 12bolts. 4 of my A-bodys came with the 3R yoked 12bolts, & it's just easier if I need to pull & swap a driveshaft or rear out of one, that I don't have an odd ball in the mix. That said, my GT-37 has a disquised 8.5 (with a 12 bolt cover) going in it. It uses a driveshaft cut down 7/8" shorter than when it had its original 12 bolt :spank: :3gears: Roger
Thanks George, I have a Chevy 8.2" with the Chevy yoke now. I had to get two different u joints to make one that would work a few years back. That is good to know I can just get the correct one now. Who knows maybe the extra one I have will work as well. Guess I will just have to check it all once I get the 12 bolt bolted in. Thanks again, Mike
Thanks Roger and George, I think I am safe with what I have, but I will check it after install and do what I have to to get it right. You guys are great!!! Thanks again, Mike
This may be a day late, and a dollar short... but I've been sitting on an extra conversion ujoint. If you're interested in it, shoot me a PM... its just taking up shelf space ou:
