Rear gears for 77 trans am?

[Bscheit65]

Does anybody know what most 77 trans am 400 6.6 had for a rear gear ratio gonna change it too 323 think it has 273 but not sure anyone know for sure off top there head? Thanks

[Aus78Formula]

It'll only be a guess until you check. If not sure then what better way than giving an oil change, no messing around jacking up and spinning wheels and counting.

[1979 Black and Tan]

it's stamped on the rear end housing

[roadking77]

I think its marked on the pass side tube kinda facing towards the front. May be a lettered code.

[Bscheit65]

I looked both those places and still couldn’t find anything let you know what I find out putting 323 gears in it

[Aus78Formula]

I'd find out what they are before you swap them or you have based the decision on nothing.

[roadking77]

Did you scrape the tube down good and clean all over. From what I recall its not real obvious until you do some scrubbing. Someone had a chart (maybe butler) that had the codes to decipher the marks. I think there is a date code as well. I'll go out on a limb and say an "s" mark is for the 2:73, but dont hold me to it.

[Aus78Formula]

It's in every Service manual too. A 2.73 ratio Posi would have 2PU.

[Bscheit65]

Yeah I scrubbed it good with a wire brush still couldn’t find anything ended up opening it up it was a 2:41 couldn’t believe how low that was didn’t know they had that!

[b_hill_86]

Keep us updated or at least me lol. My 77 has that gear or the next up but smaller than 2.73. I’ve been debating 3.08 or 3.23 with my 4 speed. Really leaning to 3.23. Almost picked up a complete 3.42 axle since price was right but I didn’t wanna go that size.

[Aus78Formula]

That was lucky you checked. Goes to show you can't swap gears simply by guessing what it might be and then jumping a step or two whichever way you prefer. By the way, that's a 2 series carrier which only allows you to go 2.56, 2.73 and up are 3 series.

[Bscheit65]

Yeah I’m still gonna get 3:23 just have to save up a little more money I just need a different carrier since it’s not  273 or above which cost about $500

[Ryoko]

I changed my 74 from an auto to a 4-speed, but left the 3.08 rear end alone. It worked out very well for me and made for a nice cruiser.

[Bscheit65]

That is an option I’ve been playing with is converting to a manual