74 Differential Stamp for 3:36 gear ratio - AX vs LR?

[Victor S.]

Hi All -

74 had two differential codes for the 3:36 that model year - both AX and LR.
Were these the same rear ends or were AX/LR installed on different engine/trans configurations? Im wondering if AX was heavy duty (or some other difference) for specific cars - but I have not seen anything documenting this.

Thanks,
Vic

[Duke W.]

Both are Positraction since that became standard on all AXLES in 1971. The difference would be one was for a small block and the other for a big block, but the NCRS Spec. Guide does not specifically state this.

AFAIK the ONLY difference between big and small block axles in that era are the side yokes. Small block axles use the "strap-type" side yokes and big blocks the "cap-type" side yokes. All other axle parts are identical for both small and big blocks.

I note that the NCRS Spec. Guide shows both AX and LR for '75 even though there was no big block option that year. Whatever the '73-'74 big block axle code is, there were probably some left over from '74 production and those not transferred to service parts were installed in '75 production, probably early on.

In the early C3 era there were as many as 18 different axle codes. By '76 is was down to six and two by the end of the C3 production. From a logistics and inventory management standpoint it certainly made sense to reduce the number of axle configuations as some were for very low production option configurations.

BTW, the "differential" is not coded. It's the AXLE that's coded. The DIFFERENTIAL CASE that mounts the ring gear, differential gears and, Positraction mechanism if so equipped, is mounted to the DIFFERENTIAL CARRIER, which is the large external casting that you see. Button it up with the AXLE COVER, and you have a complete AXLE.

Duke

[Victor S.]

Thanks Duke much appreciated - any info on which one (LR/AX) went in the big block?

[Duke W.]

I don't know, but if you have a '74 the code and side yoke type should provide the answer. If you don't have a '74, maybe someone who has one can chime in.

Duke

[Robert R.]

Hey Vic,
I checked the build sheets from my 74’s. The small block, 4sp. car with a 3.36 rear has the LR code and my big block, automatic car with a 3.08 rear has the AW code. I assume your big block car with a 4sp and 3.36 rear has the AX code.
Take care,
‘Bob

[Tom R.]

Hey Vic,
I checked the build sheets from my 74’s. The small block, 4sp. car with a 3.36 rear has the LR code and my big block, automatic car with a 3.08 rear has the AW code. I assume your big block car with a 4sp and 3.36 rear has the AX code.
Take care,
‘Bob

Great illustration of the utility using 73-82 build sheets to confirm build options!