Gear change ?

[Dan-K]

This is a continuation of an earlier thread (Swap Meet Score) . Can I run a 3.42 gear ratio with a 4 series carrier via a shim etc ? I picked up an Eaton true-trac #913A315 at a swap meet with a 4.10 gear set on it . I would prefer not to go that crazy with the gears as I dont have overdrive . Can I use a 3 series gearset on this unit or am I going to have to use the 4.10s ?

[cj847]

Assuming it is for a 12 bolt, You can use 3.73 gears on a 4 series carrier. That is as numerically low as you can go.

If I recall correctly from my jeep days, you can shim a 4 series gear to work on a 3 series carrier, but not vise versa (The pinion gear is a small diameter on 4 series gears, so the carrier is thicker, to move the ring gear towards the pinion).
The jeep vendors actually sell "thick" 4 series gears for this vs a shim.

[Mike C]

Spacer, not shims. Shims are on the outside of the bearings to adjust backlash and preload. But a higher numeric gear can be run on a lower carrier with a spacer. But I would not recommend it.

3.73 is the carrier break for the truck "4" series carrier as mentioned above, 3.07-3.42 for the "3" and less than 3.0 for the "2" series carrier.

For cars, you can get a thin gear to run 3.73 on a 4 series carrier (car break is 3.90 and up for the 4 series) I did not find a thin 3.42 gear for the trucks when I Googled FWIW.