Choosing a differential gear ratio.....

[Jrake248]

Hello all. I'm new to this group and fairly new to the world of Broncos. I acquired a 1968 that I'm doing a complete frame off restoration build with. My knowledge is fairly limited, but I'm a do-it-yourselfer. I'm in the process of purchasing the items to build front and rear axles. I'm running a Coyote swap with 10r80 and planning on running 35-37" tires. Most of the driving will be done on the street or highway, but I'll be doing some minor off roading and ripping in the dunes a bit. Front end will be a Currie Dana 44 and rear will be a Ford 9". Basically, my question is, given the 3 options of 4.10, 4.56, or 4.88 which one would suit my needs the best. Thanks

 

[Yeller]

welcome to the addiction


4.88 would be my choice with 37’s and 4.56 for 35’s. If unsure which tire, 4.88 works for all of them.

 

[Broncobowsher]

The 10r80 has a ton of overdrive. You can run a lot of gear and work great.

Our work truck has the 10r140 and the final overdrive is comparable, and that cruises just fine with stock tires and the stock 4:30 gear.

You are planning a much taller tire, but a lighter vehicle. 4.88 is the right ballpark.

The really wide spread of gearing in the 10r makes it much more forgiving to picking the axle ratio.

 

[lilthom]

I have a good set of front and rear 4.88s with lockers available.

 

[Speedrdr]

I have a good set of front and rear 4.88s with lockers available.

Sent you a PM.

Randy

 

[Apogee]

The 10R80 has three overdrive gears, with the final OD ratio in 10th being 0.64:1, taller than even the 0.67:1 in the AOD, so gear accordingly. You could easily run 5:13 gears and still have room to go numerically lower with Ø35"-Ø37" tires, not that there are that many lower gear options for the D44 (5.38 and 5.89?). Unless you're going to build it for the salt flats and top speed, 4.88 or 5.13 would be my choice, noting that I geared my axles with 4.88's with an NV4500 (0.74:1 OD) and Ø37" tires, and that's with a clutch, not a locking torque converter, mated up to a reasonably torquey 351W.

 

[Yeller]

I'll counter that some. nice part about the 10spd is that 9th is a nice short step, its supposed to shift, so you can get away without gearing for optimum performance at higher speeds, the gears are there. For example, a new raptor and raptor R both use 4.10:1 axle gearing. Now they make more power, and are boosted for more low end torque but they have the same trans, and same proposed tire size. A new bronco with less power, slightly more geared towards normal offroad and commuting with 35" tires uses 4.7:1 axle gearing, so you don't need to optimize per the old rules with a 10 speed.

 

[Madgyver]

4.88 for 37"s you have OD

 

[fordguy]

Don’t fear the gear

 

[EB70]

5.13's

 

[DirtDonk]

So are you having both axles built custom for you? Which means you have to choose your gear ratio ahead of time?
What gears are in the existing differentials?
Would be nice if they were at least low enough to drive, but the point I’m getting to is, why not build the vehicle and run just the rear with the gear of your choice and see how you like it.

Drive it around in 2 Wheel Dr. for a couple of weeks and make your decision based on actual experience.
That way you save a bunch of money and hand wringing. And while it does extend your project slightly, you’ll probably be happier in the end.

Just a thought, while you’re still in the planning stages.