1972 C10 G80 Rear axle code: gear ratio - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Cesar Diaz · 03-14-2017, 05:24 PM

I have a 1972 LWB C10 w/ 402 Engine, 4 on the floor M49 turbo Hydra matic has a G80:Not Open Diff – Positraction / Limited Slip / Typ. Gov-Lock

description from sierra gear and Axle)

I'm trying to figure out the gear ratio, I am am a novice working on this truck with my son, def not a gear head. So forgive my ignorance. I tried doing multiple searches all over the forum.

thanks

geezer#99 · 03-14-2017, 05:51 PM

THere's a gazillion threads out there. Even some youtube vids.
https://www.google.ca/webhp?sourceid...ulling+cover&*

**Already Gone** · 03-14-2017, 07:25 PM

Quote:

Originally Posted by Cesar Diaz

I have a 1972 LWB C10 w/ 402 Engine, 4 on the floor M49 turbo Hydra matic has a G80:Not Open Diff – Positraction / Limited Slip / Typ. Gov-Lock

description from sierra gear and Axle)

I'm trying to figure out the gear ratio, I am am a novice working on this truck with my son, def not a gear head. So forgive my ignorance. I tried doing multiple searches all over the forum.

thanks

WE all try to help each other on this site and a lot of times by helping someone out we learn something new ourselves. I am a little confused . You say you have a 4 on the floor and M49. M49 is a 3 speed auto trans. So are you saying someone has puled the auto trans and put in a 4 speed manual? Anyway I'm attaching a chart with the power train specs for a 72 C10. As the chart shows no big blocks with 4 speed manuals in a C10. If your truck came from the factory with a402 and auto trans you would have a 3:07 ratio.

**jocko** · 03-14-2017, 07:41 PM

G80 only indicates posi, not ratio. If you have no other gear ratio callout on the SPID, and the SPID says 402 and M49, then your truck came with a 3.07. Having said that, the only way to know what you have today is remove the cover and count the pinion and ring gear teeth and do a little division. As Greg stated, M49 is the TH automatic trans, so your trans has been changed out at some point. Does your steering column have the boss with the pinhole where the automatic shift lever would have been removed (am assuming it's gone)?

03-14-2017, 05:24 PM	#1
Cesar Diaz Registered User Join Date: Jun 2016 Location: Stevenson Ranch, CA Posts: 62	1972 C10 G80 Rear axle code: gear ratio I have a 1972 LWB C10 w/ 402 Engine, 4 on the floor M49 turbo Hydra matic has a G80:Not Open Diff – Positraction / Limited Slip / Typ. Gov-Lock description from sierra gear and Axle) I'm trying to figure out the gear ratio, I am am a novice working on this truck with my son, def not a gear head. So forgive my ignorance. I tried doing multiple searches all over the forum. thanks

03-14-2017, 05:51 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,736	Re: 1972 C10 G80 Rear axle code: gear ratio THere's a gazillion threads out there. Even some youtube vids. https://www.google.ca/webhp?sourceid...ulling+cover&*

03-14-2017, 07:41 PM	#4
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,975	Re: 1972 C10 G80 Rear axle code: gear ratio G80 only indicates posi, not ratio. If you have no other gear ratio callout on the SPID, and the SPID says 402 and M49, then your truck came with a 3.07. Having said that, the only way to know what you have today is remove the cover and count the pinion and ring gear teeth and do a little division. As Greg stated, M49 is the TH automatic trans, so your trans has been changed out at some point. Does your steering column have the boss with the pinhole where the automatic shift lever would have been removed (am assuming it's gone)?



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