What rear ends years/tranny combinations are directly compatible without any modifications? I am looking to swap out the rear end on my 70 BB 4spd with another gear ratio and am interested in the mechanical differences that would make the swap more complicated than a direct bolt-on.
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Tony -
Re: C3: Rear-end Compatibility
1963 to 1979 are all the same rear end, with minor differences.
Small blocks up to the '70s used u-bolt retainers on the inner u-joints while big block used bolts and caps. In the 70s, the small block used the cap setup also. As long as the rear you buy has the u-bolt/cap with it, it won't matter if it is different than yours.
The rear spring mounting bolt changed diameter size. I'm not sure of which year, but '78 and '79 are definitely smaller. This may have occurred a couple of years earlier. Again, this is minor. If you are buying from an individiual, they may have the bolts still or you can get them from Chevy. 7/16-14 x 3-5/16 Grp 8.900 in the Illustrations section of the '82 P&I Catalog, however, I don't have a section 8.900 in the parts.
Automatics used a larger pinion yoke, using the "400" u-joint size. Manuals used the "350" size u-joint. If you run into that, you have two choices:
- change the yoke and also the seal or the new yoke will leak
- use a 350/400 u-joint. One such is Neapco 1-0153 which you should be able to cross reference to other brands. It was also used in some Ford trucks and some larger GM cars in the '60s. While good parts stores and driveline specialty shops will know what a "350/400" u-joint is, AutoZone, Pep Boys, and so one will stare at you like you are from outer space.
Practically speaking, there are lots of 3.08 rears if you are looking for better mileage and highway usage. However, most will have the larger yoke for the Turbo 400 automatic. Lower ratios (3.70, 4.11, etc.) will commonly have the smaller yoke as they tend to be in manual cars.
It is all an easy swap. -
Two bolt sizes, two mounting plates
I mean to expand more on the '63 to '77 and '78-79 rear end bolts. The 7/16-14 x 3-5/16 is for the '78 and '79 rear. The earlier rear took a 9/16 bolt.
There were also two mounting plates - one for small holes #457977 (78,79) and one for large holes #3817582 ('63-'77).Comment
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