[tekuhn]

Originally Posted by 360Rocket

Not exactly sure why it isn't working but ??? I have no idea, maybe a difference in the carriers? It came originally as a one wheeler 3:08 from the code on the axle tube? Unless I am reading that wrong? So it started as a 3 series carrier from the factory. The axles that came with the carrier ended up being too long as well.

I think you might need to do a little detective work here. Reading between the lines of your post, with the 4.XX gears, were you using a standard Pontiac 3R u-joint and not a hybrid? All 12-bolts regardless of gear ratio would accept the same pinion yoke. By that I mean it will physically bolt on, regardless of which u-joint it's sized for. If your 4.XX gear set and your 3.XX gear set are not allowing you to use the same yoke, then there is a problem. Are both pinion gears the same bearing diameter and cut with 30 splines? You mentioned the new 3-series carrier coming with axles that were a different length. It's true that the '64-'67 A-body 12-bolts were about 1 inch narrower than the '68-'72 and had axles that were correspondingly shorter. (BTW, Pontiac went 1 inch wider two years earlier in '66). Again, your original axles should work with either carrier. Are both sets of axles retained by C-clips and with the same diameter and number of splines? Did both ring gears have the same bolt pattern and bolt circle diameter? I believe these should each fit the others carrier, although the thickness would not be correct. The only difference between a 3-series and 4-series carrier would be the ring gear offset to maintain alignment with the different pinion gear head sizes. A 12 tooth pinion head is necessarily larger in diameter than a 9 tooth. At some point you can't maintain proper ring and pinion mesh by varying the ring gear thickness and it's necessary to move the ring gear offset with the carrier.

I guess if you have this gear swap complete and working properly then you're all set, but if this is still in progress, I'd strongly recommend you thoroughly inspect all these parts and make sure you know what you're working with. All part numbers as well as dimensions and spline counts are readily available on the Internet. Start with the part number for your differential housing and take it from there so you know what you've got.