Bronco Nation

What gears do I need to buy?

Kid witha 89
Dec 13, 2021

Rank III

Dec 13, 2021

I have a 1989 base model fourth gen and the rear axle just went out. I've been looking into buying a limited slip and possibly lowering the gear ratio. What gears should I look at buying? I'm not sure what the front axle is, but I know I'm going to have to change those gears too if I change the others.
Last edited by a moderator: Dec 13, 2021

Rank 0

Dec 13, 2021

#1
Kid witha 89
I have a 1989 base model fourth gen and the rear axle just went out. I've been looking into buying a limited slip and possibly lowering the gear ratio. What gears should I look at buying? I'm not sure what the front axle is, but I know I'm going to have to change those gears too if I change the others.
There are a few variables at play. The main one is tire size and the other is intended use. In general If you are going for 35” you want a 4.56 or higher number.
Kid witha 89

🏜️Devastation caused by Elevation 🏜️

Dec 13, 2021

#2
DDaniel
There are a few variables at play. The main one is tire size and the other is intended use. In general If you are going for 35” you want a 4.56 or higher number.
Very True! Tire size is the key factor, I use to have years ago a Laredo CJ7 Jeep in which I wanted to add Larger tires, I added 35" tires I knew I had to change the front end and back end ring and pinion gear ratio.
I was running stock gears I believe 3.73s and my speedometer was off approximately 16 MPH.
I added 4.56 gears and it was almost spot on, however several years later I added 40" Gumbo Monster Mudders and that bogged me down a little bit, but it wasn't enough to make me change my gears again. Still could do some pretty good wheelin in them.
*632* Days to get A 2021 - 2022 -
2023 Big Bend - 2 Door 2.3L Velocity Blue, Squatched, Mid package, Running Boards, Roof Rack, and Engine Block heater.
DDaniel, Kid witha 89

Rank III

Dec 13, 2021

#3
DDaniel
There are a few variables at play. The main one is tire size and the other is intended use. In general If you are going for 35” you want a 4.56 or higher number.
I want to be able to run 33s, right now it just has 31s. I plan on buying a 2 inch leveling kit from Skyjacker, it should almost completely clear 33s. So should I just replace the rear end with stock gearing? (because the rear end is dead). Or should I get new gears for the front and rear and gear it down?
BroncOitis

Rank 0

Dec 13, 2021

#4
Kid witha 89
I want to be able to run 33s, right now it just has 31s. I plan on buying a 2 inch leveling kit from Skyjacker, it should almost completely clear 33s. So should I just replace the rear end with stock gearing? (because the rear end is dead). Or should I get new gears for the front and rear and gear it down?
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I’d verify the gear ratio, but you can probably get away with stock gearing. If you plan on towing or any substantial off-roading you would benefit from deeper gears. I would suggest 3.73 at a minimum, 4.10-4.27 if you plan for towing or off roaring.
Kid witha 89

Rank III

Dec 15, 2021

#5
The stock gearing is 3.55 right now, but I was thinking of going down to 4.10. Thanks for the advice

🏜️Devastation caused by Elevation 🏜️

Dec 15, 2021

#6
Kid witha 89
The stock gearing is 3.55 right now, but I was thinking of going down to 4.10. Thanks for the advice
In my opinion a 4.10 front and rear with 33" tires would be ideal, however "I'm not an expert at this," I'm just basing it off my past experience.
*632* Days to get A 2021 - 2022 -
2023 Big Bend - 2 Door 2.3L Velocity Blue, Squatched, Mid package, Running Boards, Roof Rack, and Engine Block heater.
Kid witha 89

Rank III

Dec 15, 2021

#7
BroncOitis
In my opinion a 4.10 front and rear with 33" tires would be ideal, however "I'm not an expert at this," I'm just basing it off my past experience.
That's what I was thinking too, based on other peoples comments and some other forums and stuff I've read online

Rank VI

Dec 15, 2021

#8
I got the Badlands, Auto, and it has 4.43 gears in it. Plenty of power, and I’m averaging 19.5MPG Around my little rural town, 18.5 on the highway and toll roads.

Rank III

Dec 15, 2021

#9
Padams7
I got the Badlands, Auto, and it has 4.43 gears in it. Plenty of power, and I’m averaging 19.5MPG Around my little rural town, 18.5 on the highway and toll roads.
I got the custom, auto (c6 tranny) and it has 3.55 gears in it. No power at all, I'm averaging 15mpg in town, maybe 16 on the highway.

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