Rear differential gear swap 93' f-150 2x4 - Ford Forums

ductmasterd · 05-03-2009, 19:11

Hi, my differential broke today and needs replacement. It's code is S824B, meaning it's an 8.8" with a 2.73 gear ratio. I have a manual transmission
(M5OD R2 4x2) I was wondering, how would changing the gear ratio to a lower gear (I had 3.73 in mind) change the driveability of the vehicle? Would it affect the transmission in any way?

Thanks in advance
-Dave

Steve83 · 05-05-2009, 00:07

That's not what that code means. That's where it was built.

No, the axle gears don't affect the trans. A numerically higher ratio will make the tires turn over a little less for each driveshaft rev, meaning you'll feel more acceleration at low speeds, and but it'll rev higher at high speeds, meaning you probably won't be able to go as fast. Depending on which engine you have, how it's tuned/running, and how you drive, that could be good or bad. If you're using oversized tires, this swap could balance them out & bring the truck closer to its original feel.

ductmasterd · 05-05-2009, 14:22

Thank you Steve for the reply.

I'm running 31 x 10.50 x r15 BF Goodrich MudTerrain
Engine is a 4.9l EFI straight-six.

I was hoping to find a BW T-18 to stick in there and ditch the 5 speed.

**360ci** · 05-05-2009, 20:28

2.73 is rather low. A 3.73 is a good jump. You might see better mileage around town due in part to less clutch slip and more low end torque. Highway mileage will suffer a bit of course, as to be expected. I think you'll like the 3.73. If you plan on increasing tire size further (32-33") I'd get the 4.10s installed.

Yukon Gear & Axle is a good informative site for gears. I got a 4.56 front and rear setup a couple years ago and haven't had any problems!

Steve83 · 05-05-2009, 23:01

My '83 Bronco has a '95 4.9L, '78 NP435, 3.08, 32x11.50R15, and it does pretty well. I can tow anything with wheels (up to an 18-wheeler-sized dump truck) and a lot of things without (a house off its foundation, a construction office trailer, a 40hp tractor, a 30yd construction dumpster...), but I can also set the cruise over 100mph.

So I doubt you'll be happy with such low gears. The lowest I'd go would be 3.55, but for me, even that is too low. I could barely hit 90 when I used them. Yeah, the takeoff was GREAT, but the speed was pitiful.

Why are you so anxious to ditch the OD? Most people WANT it, although most try for the ZF (M5OD-HD) instead of the Mazda that you have. However, havack (BroncoData) put one in his 5.0L Bronco and loved it.