70cutman

I have a 70 cutlass with a 350 that I'm putting a 455 along with a 400 short tail trans. Also going in is a 12 bolt rear end from what seems to be a 69-70 gto with 4:56, but i wiuld want to change gears to 3:73.
Would any one be able to tell me what parts I would need and what changes to make if any?

2blu442

You'll need a different driveline length, and the TH400 has an electrical kickdown switch mounted to the gas pedal vs the TH350 with a mechanical cable. You'll likely have to change the speedometer drive gear in the transmission once you get the rear end gears and tire size decided. That's what comes to mind for me, others will have to add what I've missed. Physically everything bolts up and should be a straightforward swap. John

70cutman

Would you happen to know where I can pull that drive line, or would I be better off cutting and balancing the one I have?
Also, where can I find the switch and assembly for the gas pedal?

70cutman

here are some pics

70cutman

Here are some pics
If the Trans is a short tail, do I still need to get a different driveline?

jensenracing77

i don't know what that rear end is but a th400 with an O type (12 bolt cover) needs a 54 1/2 to 55 inch drive shaft. not sure your rear end will be the same length from a Pontiac. if you don't have one you will need a yolk for a th400.

70cutman

the cast id on it reads 3869278. supposed to have been from a gto. when I google search that id it says its from a 70 gto. I def know its a 12 bolt in and out.

joe_padavano

The Chevy 12 bolt uses a different driveshaft length than the Type O axle. Yes, even the short tail TH400 needs a different driveshaft.

Since you have to relocate the trans crossmember for the TH400, you will need to change the front and intermediate e-brake cables.

And DO NOT buy "455" motor mounts unless you change the frame mounts. If you keep the 350 frame mounts then use the matching 350 motor mounts.

70cutman

is the 70 gto 12 bolt the same as the chevy 12 bolt? (iow does the same apply?)

joe_padavano

If they are both 8.875" ring gear axles with twelve bolts holding the ring gear to the carrier, then yes. GM made a number of different axle housings with twelve bolts holding the cover. Contrary to popular belief, the "twelve bolt" designation really refers to the number of bolts holding the ring gear.