I think my C10 rear axle has a 2.5? rear gear ratio / is this true - The 1947 - Present Chevrolet & GMC Truck Message Board Network

G-NUT · 03-21-2018, 01:47 PM

I was given a rear axle from my mother-in-law's boyfriend; it came out of a 1984 Chevrolet C10 2wd that he's had for years, but it's been sitting in his field for quite a few years. I just tried the whole mark the drive shaft yolk and wheel hub and spin / count thing from all the YouTub videos I've found, and what I seem to come up with is 2.5? . I have an open diff. I've never heard of a truck having a gear ratio higher than 2.73s. So is there a 2.5? that would have been in the truck. I asked the guy I got if from if he'd ever changed them out and he said no. There is no tag on the axle to help me identify what they might be.

**mongocanfly** · 03-21-2018, 03:15 PM

easiest way is pop the cover off and count the teeth....then divide...
my 85 had 2.73s...I thought that was high as tney went on trucks....

G-NUT · 03-21-2018, 04:50 PM

Took the cover off just a bit ago. Found a part number on the edge of the ring gear. The number is as follows:
W GM 1235401 16 41 10 83

Also, I counted the teeth on the ring gear and pinion gear:
Ring gear had 41 teeth
Pinion gear had 16 teeth.

Found a part number on my axle tube: BN3 G300 1
And two part numbers on my center chunk, one on the left and right of the center: what looks like GM36 on one side and looks like maybe 14055251 or 405525 on the other side. Not sure what those mean.

Keith Seymore · 03-21-2018, 05:00 PM

41/16 = 2.56, so that's pretty conclusive.

2.56 was the base axle in some configurations.

K

https://www.gmheritagecenter.com/doc...olet-Truck.pdf

**mongocanfly** · 03-21-2018, 05:12 PM

wow! 2.56s....I never knew they went that high on trucks...and I thought my 2.73s were high...

G-NUT · 03-21-2018, 05:40 PM

Thanks for the info.

I'm wanting to change to a 3.42 and a limited slip. Can I do this with this 10 bolt 8.5 axle that contains an open diff and 2.56 gears? I've read some say you can while some say you cannot.

**mongocanfly** · 03-21-2018, 05:47 PM

use the rpm calculator before you decide on gearing..http://www.csgnetwork.com/multirpmcalc.html

**Captainfab** · 03-21-2018, 11:05 PM

You will just have to determine what series the carrier is for the 2.56 gears and whether or not there is a 3.42 gear set for that series of carrier. One of the many differential parts suppliers should be able to help you figure it out. According to what I'm seeing from both Yukon and Richmond, the carrier will need to be replaced with a 2.73 and lower carrier. You may want to verify that.

Quote:

Originally Posted by G-NUT

Thanks for the info.

I'm wanting to change to a 3.42 and a limited slip. Can I do this with this 10 bolt 8.5 axle that contains an open diff and 2.56 gears? I've read some say you can while some say you cannot.

61K10 · 03-22-2018, 01:45 PM

If going with a posi you are going to replace the carrier anyway. no problem.

**mongocanfly** · 03-22-2018, 02:15 PM

^^^^agreed^^^^....new diff/new gears...problem solved

G-NUT · 03-22-2018, 05:02 PM

Thanks for the information guys.

03-21-2018, 01:47 PM	#1
G-NUT Registered User Join Date: Apr 2014 Location: Baldwin County, Alabama Posts: 163	I think my C10 rear axle has a 2.5? rear gear ratio / is this true I was given a rear axle from my mother-in-law's boyfriend; it came out of a 1984 Chevrolet C10 2wd that he's had for years, but it's been sitting in his field for quite a few years. I just tried the whole mark the drive shaft yolk and wheel hub and spin / count thing from all the YouTub videos I've found, and what I seem to come up with is 2.5? . I have an open diff. I've never heard of a truck having a gear ratio higher than 2.73s. So is there a 2.5? that would have been in the truck. I asked the guy I got if from if he'd ever changed them out and he said no. There is no tag on the axle to help me identify what they might be. __________________ '84 Suburban C10 Silverado - laying pinchweld to the ground on 22/24. /Porterbuilt / Accuair / Bonspeed / Landsail / Auburn Gear / Richmond Gear / Moser / Raybestos / ProMaxx / Edlebrock / Street Demon / Taylor Wire / K&N / MSD / KillMat / SOLD: 1985 GMC Sierra Classic 2500 3+3 Crew Cab Long Bed

03-21-2018, 03:15 PM	#2
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,663	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true easiest way is pop the cover off and count the teeth....then divide... my 85 had 2.73s...I thought that was high as tney went on trucks.... __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver Last edited by mongocanfly; 03-21-2018 at 03:35 PM.

03-21-2018, 04:50 PM	#3
G-NUT Registered User Join Date: Apr 2014 Location: Baldwin County, Alabama Posts: 163	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true Took the cover off just a bit ago. Found a part number on the edge of the ring gear. The number is as follows: W GM 1235401 16 41 10 83 Also, I counted the teeth on the ring gear and pinion gear: Ring gear had 41 teeth Pinion gear had 16 teeth. Found a part number on my axle tube: BN3 G300 1 And two part numbers on my center chunk, one on the left and right of the center: what looks like GM36 on one side and looks like maybe 14055251 or 405525 on the other side. Not sure what those mean. __________________ '84 Suburban C10 Silverado - laying pinchweld to the ground on 22/24. /Porterbuilt / Accuair / Bonspeed / Landsail / Auburn Gear / Richmond Gear / Moser / Raybestos / ProMaxx / Edlebrock / Street Demon / Taylor Wire / K&N / MSD / KillMat / SOLD: 1985 GMC Sierra Classic 2500 3+3 Crew Cab Long Bed

03-21-2018, 05:00 PM	#4
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,213	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true 41/16 = 2.56, so that's pretty conclusive. 2.56 was the base axle in some configurations. K https://www.gmheritagecenter.com/doc...olet-Truck.pdf Attached Images __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ Last edited by Keith Seymore; 03-21-2018 at 05:10 PM.

03-21-2018, 05:12 PM	#5
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,663	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true wow! 2.56s....I never knew they went that high on trucks...and I thought my 2.73s were high... __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

03-21-2018, 05:40 PM	#6
G-NUT Registered User Join Date: Apr 2014 Location: Baldwin County, Alabama Posts: 163	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true Thanks for the info. I'm wanting to change to a 3.42 and a limited slip. Can I do this with this 10 bolt 8.5 axle that contains an open diff and 2.56 gears? I've read some say you can while some say you cannot. __________________ '84 Suburban C10 Silverado - laying pinchweld to the ground on 22/24. /Porterbuilt / Accuair / Bonspeed / Landsail / Auburn Gear / Richmond Gear / Moser / Raybestos / ProMaxx / Edlebrock / Street Demon / Taylor Wire / K&N / MSD / KillMat / SOLD: 1985 GMC Sierra Classic 2500 3+3 Crew Cab Long Bed

03-21-2018, 05:47 PM	#7
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,663	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true use the rpm calculator before you decide on gearing..http://www.csgnetwork.com/multirpmcalc.html __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

03-22-2018, 01:45 PM	#9
61K10 Registered User Join Date: Feb 2012 Location: pleasant valley--placerville ca Posts: 3,039	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true If going with a posi you are going to replace the carrier anyway. no problem. __________________ 1961 chevy K10 my build is------------61K10 build

03-22-2018, 02:15 PM	#10
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,663	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true ^^^^agreed^^^^....new diff/new gears...problem solved __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

03-22-2018, 05:02 PM	#11
G-NUT Registered User Join Date: Apr 2014 Location: Baldwin County, Alabama Posts: 163	Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true Thanks for the information guys. __________________ '84 Suburban C10 Silverado - laying pinchweld to the ground on 22/24. /Porterbuilt / Accuair / Bonspeed / Landsail / Auburn Gear / Richmond Gear / Moser / Raybestos / ProMaxx / Edlebrock / Street Demon / Taylor Wire / K&N / MSD / KillMat / SOLD: 1985 GMC Sierra Classic 2500 3+3 Crew Cab Long Bed

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