10 bolt ring/pinion question

[kodiakisland]

I'm working on a 91 jimmy for my 15yo son. It has 10 bolt front and rear with 3.42 gears and auto trans. He will not be doing any hard core wheeling in the next few years, mostly highway/ mild off road while learning to drive.

In the next few weeks we will be pulling the front axle to replace ball joints, tie rods, drag link, rotors and calipers, and also putting in skyjacker 2.5in springs. The plan is to find some 16X8 wheels and run 33in tires.

Will the carrier have to be changed when going lower than 3.42, or is that only 12 bolts? What is the best choice for a gear change, 3.73, 3.90, or 4.10? Again, this will be mostly driven on the road 65mph max. I'm leaning toward 3.90s.

I figured as long as I have the axle out I might as well change out the gears. I plan to take the axle to a shop and have someone who knows what they are doing replace it, as I think it's above my ability.

 

[fmstruck]

You should be able to get a thick gear, if nothing else. If you have a 700R4 tranny, I would go 4.10s at least. That still leaves the final ratio at 2.87 through the overdrive.

 

[kodiakisland]

What do you mean by a thick gear?

 

[fmstruck]

The reason that there is a break between carriers is because the deeper the gear, (higher numerically) the smaller the pinion is. When you make the pinion smaller, the ring gear has to move toward the pinion. On the 3 series carrier, for instance, the ring gear mounting surface is located further to the left, or further from the pinion gear centerline. On a 4 series carrier, that mounting surface is moved toward the pinion centerline. A thick gear allows you to run a 4 series gear on a 3 series carrier without using a spacer.