66 Differential Question

[66cuda-s]

Hello. I have a '66 Barracuda Formula S that I am working on. I am a bit confused about the differential. It has the 7-1/4" non-Sure Grip with 9" drums. The Build sheet says that it came with a Sure Grip (code 408 ) with a 3.23:1 ratio (code 404). The front drum brakes are 10" and I would think that the rear would be the same. It looks like this axle was changed out at some point. Is there any way to tell whether the car came with an 8-3/4" axle? I would like to return the car to original as much as possible. My service manual implies that all Valiants (which I think includes Barracudas) came with 7-1/4" differentials. Even if the car came with a 7-1/4", I would like to upgrade that to the sure grip if possible (and 10" drums). Thanks.

 

[toolmanmike]

I dont think 7 1/4s had posi. That car was born with a 8 3/4 sure grip I'm sure. toolmanmike

 

[toolmanmike]

The 408 and 404 codes are correct for a 8 3/4 with a 3:23 gear. I'll bet
the rear end got switched at some time with one from a slant 6 car.
toolmanmike

 

[66340SEDAN]

Yes! 7 1/4 rears had a sure-grip that was optional, it is like the 8 3/4 ones except smaller. They are very hard to find, one of the mopar magizines ran a short article about them, they came across one in a 1968 225 Barracuda with a 7 1/4 sure-grip in a junkyard! I parted out a 66 Barracuda "S" that was very rusty, 273 hp, 4-speed, disc brakes and a 7 1/4 rear. Not sure if it was original that way but the car was mostly untouched. My dads friend has a 66 Barracuda "S" with a 7 1/4 rear that he owned since new, I thought it was not possible but who knows for sure, Chrysler did some strange things in the 60's! Not sure about the codes but that would tell you for sure, may want to do some research!