sorry another gear ratio question

[K5 Silverado]

Okay I found a 79 full size pick up it has a 12 bolt rear. It is a heavy half ton with a 400 motor. I dont know what it would have in the front if some one know maybe they could tell me. But what would the most likely gear ratio be in it? I search for a axel tag but couldnt find one. How much better is the 12 bolt compared to the 10 bolt.

 

[Hogback Fabrication]

The front could be either a 10 bolt or a dana 44. It doesn't really matter, they are very similar in virtually every way.

The gear ratio could be a bunch of different ratios, but I would guess that 3.73 was most common on 1/2 tons of that era. The only real way to check is to pull the cover and read the numbers on the ring gear.

The (truck) 12 bolt is marginally stronger than a 10 bolt. It has slightly larger axle shafts than early 10 bolts (pre '88 or so) and has the same size axle shafts as later 10 bolts. 12 bolt shafts and later 10 bolt shafts are both 30 spline 1.31" diameter shafts. Earlier 28 spline 10 bolt shafts are more like 1.28" IIRC.

The 12 bolt has an 8.875" ring gear while the 10 bolt has a 8.5" ring gear. The truck 12 bolt has tiny pinion bearings that are notorious for failing. The wheel bearings aren't notoriously reliable either.

In reality, there isn't much strength difference between the two. If you broke a 10 bolt, you probably would have broken a 12 bolt as well.

 

[imiceman44]

Okay I found a 79 full size pick up it has a 12 bolt rear. It is a heavy half ton with a 400 motor. I dont know what it would have in the front if some one know maybe they could tell me. But what would the most likely gear ratio be in it? I search for a axel tag but couldnt find one. How much better is the 12 bolt compared to the 10 bolt.

The 12 bolt is pretty much the same, has a bigger ring gear, and smaller pinion than the 10 bolt.
I wouldn't take that as a plus for either axle.
As for the front, 79 was still a mixed year so it could be D44 front or 10 bolt front, again no major difference.
Gear ratio i wanna venture and say most likely 3.73, but to confirm lift one tire mark the tire with a chalk line vertical at the bottom right where it touches the ground, and mark the driveshaft with a chalk line on the side from the yoke and to the axle housing.
Rotate the tire roughly 2 full turns and stop where the driveshaft line meets the axle line.
Multiply the number of rotations by 2 and you have the ratio:
If you turned the tire almost 1 3/4 turns then you have a 3.73
If you turned the tire almost 1.5 turns you have 3.08
If by any chance you turned little more than 2 then you have the rare 4.10
All that is assuming no one already changed gears on the axles.

 

[K5 Silverado]

yeah my 10 bolt is fine just has 4:11s and the front has 3:73 so the guy told me he would sell my both axels for 200 ther is no slop in the rear of the 12 bolt. I just want to match the gears and then later on do thew 3/4, 1 ton swap. Thank guys I really thank you for the help this site has given me.