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.

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....

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.

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

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...

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.

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

Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true
 

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.

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.

Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true
 

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

Re: I think my C10 rear axle has a 2.5? rear gear ratio / is this true
 

Thanks for the information guys.