How To Find Your Rear Differential Gear Ratio

May 22, 2019 | Trucks

Ever wonder how to find the gear ratio for your rear differential? This will help you find your gear ratio on a Ford or GMC/Chevrolet Truck.

First, you’re going to need to locate the manufacturer’s sticker on your truck with the code. Here is a video that will show you where to find that sticker:

Ford places their sticker on the driver’s side door at about thigh height. It’s visible when you open the door (usually on the door frame).

GM has a sticker placed in the glove box. If your GM vehicle doesn’t have this sticker (sometimes they don’t unfortunately) you may need to take your VIN to a dealer ask them to look it up for you.

Second, cross-check the code on your sticker with the ones listed below. This is usually a little easier on a Ford than GM. I’ve listed below all the axle codes that I am aware of for these manufacturers. Keep in mind if your rear differential has ever been modified or replaced with another, these codes may no longer represent your actual rear differential gears.

Ford Axel Codes and Their Corresponding Information

2004 Ford Super Duty Axle Codes:

31 — 3.73 non-limited slip, F-250/Excursion
32 — 4.10 non-limited slip, F-250
41 — 3.73 non-limited slip, F-350
61 — 3.73 non-limited slip, F-350
73 — 4.30 non-limited slip, F-450
75 — 5.38 non-limited slip, F-450
78 — 4.88 non-limited slip, F-450
81 — 3.73 non-limited slip, F-350
88 — 4.88 non-limited slip, F-350
95 — 5.38 non-limited slip, F-550
98 — 4.88 non-limited slip, F-550
C1 — 3.73 limited slip, F-250/Excursion
C2 — 4.10 limited slip, F-250/Excursion
C3 — 4.30 limited slip, F-250/Excursion
D1 — 3.73 limited slip, F-350
D2 — 4.10 limited slip, F-350
D3 — 4.30 limited slip, F-350
E2 — 4.10 limited slip, F-350
E3 — 4.30 limited slip, F-350
EW — 4.10 limited slip, F-350 (ambulance package)
F1 — 3.73 limited slip, F-350
F2 — 4.10 limited slip, F-350
F6 — 4.56 limited slip, F-350
G3 — 4.30 limited slip, F-450
G5 — 5.38 limited slip, F-450
G8 — 4.88 limited slip, F-450
GW — 4.88 non-limited slip, F-450
K5 — 5.38 limited slip, F-550
K8 — 4.88 limited slip, F-550
KW — 4.10 non-limited slip, F-550

2007 Ford Super Duty Axle Codes:

37 — 3.73 non-limited slip
3L — 3.73 limited slip
41 — 4.10 non-limited slip
43 — 4.30 non-limited slip
48 — 4.88 non-limited slip
4L — 4.30 limited slip
4N — 4.10 limited slip
4W — 4.10 limited slip (ambulance package)
53 — 5.38 non-limited slip
5L — 5.38 limited slip
8L — 4.88 limited slip

2008 Ford Super Duty Axle Codes:

35 = 3.55 non-limited slip
3J = 3.55 limited slip
37 = 3.73 non-limited slip
3L = 3.73 limited slip
4L = 4.30 limited slip
4N = 4.10 limited slip

But wait…. there’s more. Here’s another chart. Brace yourself.

Thanks Ford. For all that code.

GMC / Chevrolet Axel Codes

RPO is the acronym for “Regular Production Option.” I’ve included some GM codes for front axels too, just in case you need it.

There you have a lot of rear differential axle codes. Hopefully the code you’re looking for it listed above… or it might really grind your gears. Pun intended.

Dodge or Chrysler… sorry, I got nothing for you.