Ring and pinion gear swap-Worth it?

[CheyLadd]

I have a 72 4X4 shortbed with sm465 and 31" tires. Glovebox says 3.73's but after looking at the rpms I should be turning, it is showing rpm's for 4.11 instead so some PO swapped them out at some point. As you know 1st or L is useless except for 4 wheeling.

Here is my question: Is it possible to gear it such (say with 3.08's) that 1st or L becomes a real 1st gear, thus giving me all 4 usable gears. I don't offroad with it much so I am not concerned about having a crawler gear. I have heard that there are no synchros in 1st. Does that make it too hard to use? I would really like to make the truck more drivable on a daily basis so I am just looking at options right now.

[Burt4x4]

I have been driving a SM465 sence 1993. Started with 3.73s 33s first gear or granny gear is very deep. You can certainly use it on take off, then switch to second gear almost right away so even if you swap out to 3.08 you could still takeoff in second from a stop. I don't think diff gears are gonna change your 465's behavior much.
You cannot down shift from second to first while rolling..well with a bit of grinding you can get it in hahahaha Second to First has no syncros.
Just tell your brain you have a 3speed with granny low

[Yukon Jack]

Yep, gotta agree with ole' Burt - a gear swap isn't going to make any difference with your granny gear.

[Blazer1970]

If you are using a factory tach, it is most likely not correct. All of them that I have seen read at least several hundred RPM high.

[og350]

well i have a 71 4x4 with 4.11's with 35's and it had the sm465 with the 205 when i bought it. it really screamed over 50 in fourth. i didnt have a tach so no clue on the r's. i swaped it for a th400 with a 208 and put in a tack. i like it alot better. at 70 it sits just under 3000 rpm. it is not at fun as the stick but i didnt like shifting that much. good luck i am going to do gears this winter so let me know what you do.

[72 CustomCamper]

Granny will never act like a normal 1st. Granny is 6.55:1 and 2nd is 3.58:1...


Chuck

[CheyLadd]

I am using an aftermarket tach and am pretty sure it is accurate. I guess using 1st is out of the question so now I have to decide about swapping gears simply for the lower rpms on the freeway. Are there any good how-tos on gear swapping? The only quote I got was $1600 for both axles and it would take a lot of gas to make that pay for itself. I have done a lot engine wise but have never been into a differential and worry about not knowing terminology.

[Blazer1970]

Originally Posted by og350

well i have a 71 4x4 with 4.11's with 35's and it had the sm465 with the 205 when i bought it. it really screamed over 50 in fourth. i didnt have a tach so no clue on the r's. i swaped it for a th400 with a 208 and put in a tack. i like it alot better. at 70 it sits just under 3000 rpm. it is not at fun as the stick but i didnt like shifting that much. good luck i am going to do gears this winter so let me know what you do.

Not sure what you accomplished here, but the SM465, TH400, NP205 and NP208 are all direct drive (1:1) in high gear. The motor would actually turn higher RPMs with the TH400 since there is slip in the torque converter.