TAC Tech => Tips & Tricks => Topic started by: Bscheit65 on February 04, 2019, 11:47:25 PM

Title: Rear gears for 77 trans am?
Post by: Bscheit65 on February 04, 2019, 11:47:25 PM
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
Title: Re: Rear gears for 77 trans am?
Post by: Aus78Formula on February 05, 2019, 07:02:29 AM
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.
Title: Re: Rear gears for 77 trans am?
Post by: 1979 Black and Tan on February 05, 2019, 12:37:23 PM
it's stamped on the rear end housing
Title: Re: Rear gears for 77 trans am?
Post by: roadking77 on February 05, 2019, 05:33:12 PM
I think its marked on the pass side tube kinda facing towards the front. May be a lettered code.
Title: Re: Rear gears for 77 trans am?
Post by: Bscheit65 on February 06, 2019, 01:01:50 AM
I looked both those places and still couldn’t find anything let you know what I find out putting 323 gears in it
Title: Re: Rear gears for 77 trans am?
Post by: Aus78Formula on February 06, 2019, 01:17:03 AM
I'd find out what they are before you swap them or you have based the decision on nothing.
Title: Re: Rear gears for 77 trans am?
Post by: roadking77 on February 06, 2019, 08:09:06 AM
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.
Title: Re: Rear gears for 77 trans am?
Post by: Aus78Formula on February 06, 2019, 08:11:52 AM
It's in every Service manual too. A 2.73 ratio Posi would have 2PU.
Title: Re: Rear gears for 77 trans am?
Post by: Bscheit65 on February 10, 2019, 11:31:14 PM
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!
Title: Re: Rear gears for 77 trans am?
Post by: b_hill_86 on February 11, 2019, 12:05:02 AM
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.
Title: Re: Rear gears for 77 trans am?
Post by: Aus78Formula on February 11, 2019, 03:08:21 AM
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.
Title: Re: Rear gears for 77 trans am?
Post by: Bscheit65 on February 11, 2019, 10:29:13 AM
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
Title: Re: Rear gears for 77 trans am?
Post by: Ryoko on February 11, 2019, 05:20:02 PM
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.
Title: Re: Rear gears for 77 trans am?
Post by: Bscheit65 on February 12, 2019, 12:45:13 AM
That is an option I’ve been playing with is converting to a manual
Title: Re: Rear gears for 77 trans am?
Post by: firebirdparts on February 23, 2019, 04:00:52 PM
2.41 is the most common for a 77 T/A, for what that's worth.  It's typical.

I suppose though, since you need another carrier, you ought to think about a brand new one.  I pulled out a lot of ruined spider gears when we were parting stuff out.
Title: Re: Rear gears for 77 trans am?
Post by: Aus78Formula on February 23, 2019, 07:00:41 PM
Also, look for entire rear axles with the diff you want. It's easier to set up or simply to fit as is, use it as an excuse to change leafsprings etc if needed. Generally, if you feel the diff ratio isn't quite ideal, then it's often more work than the result to simply go one step unless fine tuning, the results would still be similar, unless that's what you are after.
Title: Re: Rear gears for 77 trans am?
Post by: highway star on March 01, 2019, 03:06:43 AM
https://www.summitracing.com/parts/etn-19559-010/overview/

AND

https://www.summitracing.com/parts/msr-a3079gmtk
Title: Re: Rear gears for 77 trans am?
Post by: Garry on March 03, 2019, 03:05:20 AM
If you're not going to be excessively hard on it you might be able to use a spacer with your 2 series carrier. You can buy ring gear spacers through summit or jegs.

(http://image.superchevy.com/f/8844523+w667+h1000+q80+re0+cr1/p113376_image_large.jpg)

Quote from Super Chevy

"Ring gear spacers like this steel unit from Summit can be used to mount a 3-series gear on a 2.56-style carrier. The carrier has a thicker inside-diameter gear register that offers more surface area than other carriers, so Moore feels this is not a bad compromise. Summit offers this steel spacer with ARP bolts for under $30."

Title: Re: Rear gears for 77 trans am?
Post by: Garry on March 03, 2019, 03:21:38 AM
When I say excessively hard I'm talking about any form of boost.
Title: Re: Rear gears for 77 trans am?
Post by: Fbird on July 30, 2019, 09:34:47 AM
a couple of centuries ago they used to make a "thick" gear just for this situation!! been a LONG time now but 3.42 and 3.73 were always the typical swap.