Question about determining Axle Ratio

**wtlyn72** · 03-08-2008, 10:28 PM

Hi,

I'm looking into the towing specs on my truck per the users manual. With my truck type, there are two options listed under axle ratio (3.73, 4.10). Can anyone tell me how to find out what the axle ratio on my truck is?

Thanks,
Theresa

**Pete95Sierra** · 03-08-2008, 10:40 PM

what kind of truck is it? someone will help you here for sure dont worry...

**wtlyn72** · 03-08-2008, 10:44 PM

Thanks. It is a 2003 Silverado 1500HD v8 6.0l crew cab with 4 x 4.

Theresa

**95CTburb19** · 03-09-2008, 12:36 AM

in the glovebox you will see a sticker with a series of number/letter combinations. These are RPO codes and you can look up online what they stand for then match that to the ones in your glovebox.

**MrShorty** · 03-09-2008, 08:08 PM

Correct, if you're certain the gears are the same as installed at the factory, you can use the RPO codes to determine what was installed at the factory.

Alternatively, you can jack up the rear end, rotate the tires through one revolution if you pick both tires up, or through two revolutions if you only lift one tire, and count the number of times the driveshaft rotates.

**84fiero123** · 03-09-2008, 08:59 PM

I really do need to post that RPO list I have on here, it is 180 pages long though.

Here is a link to a RPO decoder on the web courtesy of our friends with corvettes.

http://s-series.org/rpo/

**hunky** · 03-10-2008, 07:59 AM

Go to the dealership,give him your VIN number,he can then give you the info. you are looking for.

**dwill3015** · 03-10-2008, 10:34 AM

I wonder if we have any GM techs here that can do VIN decoding. Here is a link to a VIN decode I had done on my Silverado on a diesel truck site. It is very detailed.

**WhosDatGuy** · 03-10-2008, 04:37 PM

My rear end is not factory, the elderly gent that I bought the truck off forgot the ratio, how can I find out what gears I'm running.

Cheers

**MrShorty** · 03-10-2008, 05:48 PM

Originally Posted by WhosDatGuy

My rear end is not factory, the elderly gent that I bought the truck off forgot the ratio, how can I find out what gears I'm running.

Cheers

Method 1 (If you need to change the diff fluid anyway): Open differential. Count the # of teeth on the ring gear and the # of teeth on the pinion gear. RG/PG=gear ratio

Method 2: Jack up both rear wheels. Put transmission/transfer case in N. Rotate rear wheels through one revolution while counting the # of times the driveshaft rotates. DS rotations/tire rotations=gear ratio. Often times, I prefer to jack up only one rear wheel and count the DS rotations through 2 rotations of that one tire. 2*DSrotations/tirerotation=gear ratio. I often prefer this because, with an open diff (or anything that behaves like an open diff like the stock G80) there might be some question with both wheels in the air if both wheels rotated exactly together.