Determining Gear Ratio

tinyfootprints · January 4, 2011

I bought a used a 2007 Sierra SLT Crew and noticed that some of these trucks have an optional 3.73 ratio and some have the standard 3.42. Is there an easy way to determine which ratio my truck has?

GMstrong · January 4, 2011

I think you have the 4L65 with the 3.73s

Stevens03 · January 4, 2011

Look in the glove box for the RPO codes, look for GU6 = 3.42, GT4 = 3.73, or GT5 = 4.10

Most likely will be one of the 3 options. And the trans is the 4L60e 4-speed trans, not the 4L65e. That one hasn't been used since 2004-5. The Vmax (6.0L) used the 4L70e if your wondering.

GMstrong · January 4, 2011

the 4L65-E (RPO M32) Was used in the 6.0L vortec 4L65 is just a up to date 4L60 they used it in the 05-06 gto and the 05 corvettes,gmc sierra 1500 and 2500 and also the denali.

jim brock · January 4, 2011

The above options are the best. If none of that works for you, jack up the rear end. Mark the driveshaft and the rear wheel. Carefully rotate the driveshaft counting revolutions until the wheel makes a complete rotation. It the driveshaft rotates a little less than 3-1/2 times your in the 3.42 ballpark. If it rotates 3-3/4 turns it might be a 3.75. Take your time with this for accurate results.

Stevens03 · January 5, 2011

the 4L65-E (RPO M32) Was used in the 6.0L vortec 4L65 is just a up to date 4L60 they used it in the 05-06 gto and the 05 corvettes,gmc sierra 1500 and 2500 and also the denali.

Its not an update.. its a heavy duty version of the 4L60e... and was only used for a year or two. The 4L70e replaced it.

mc7719 · January 5, 2011

Look in the glove box for the RPO codes, look for GU6 = 3.42, GT4 = 3.73, or GT5 = 4.10

tinyfootprints · January 5, 2011

Look in the glove box for the RPO codes, look for GU6 = 3.42, GT4 = 3.73, or GT5 = 4.10

Most likely will be one of the 3 options. And the trans is the 4L60e 4-speed trans, not the 4L65e. That one hasn't been used since 2004-5. The Vmax (6.0L) used the 4L70e if your wondering.

Thanks! RPO code is GT4 so my ratio is 3.73. I am looking at running some 33" Mickey Thompson ATZ's and was hoping I didn't have the 3.42 since that would mean new gears as well.

nickvrebel · January 5, 2011

it would be best to jack up the rear and count the rotations anyway, I know the purchaser of my old truck would be surprised if they open the rear diff and find out that although the RPO codes indicate the truck has a 3.42 open diff., in reality there is a Eaton Limited Slip (LSD) with a set of Yukon 3.73 gears in there lol

MonkeyBiz · February 24, 2011

Look in the glove box for the RPO codes, look for GU6 = 3.42, GT4 = 3.73, or GT5 = 4.10

Most likely will be one of the 3 options. And the trans is the 4L60e 4-speed trans, not the 4L65e. That one hasn't been used since 2004-5. The Vmax (6.0L) used the 4L70e if your wondering.

Curious what you guys make of this. I have the original window sticker for my truck. It says that it has 4:10 rear end. Glove box has a GT4 RPO. Vin number on sticker matches truck...

Gone Again · February 25, 2011

Look in the glove box for the RPO codes, look for GU6 = 3.42, GT4 = 3.73, or GT5 = 4.10

Most likely will be one of the 3 options. And the trans is the 4L60e 4-speed trans, not the 4L65e. That one hasn't been used since 2004-5. The Vmax (6.0L) used the 4L70e if your wondering.

Curious what you guys make of this. I have the original window sticker for my truck. It says that it has 4:10 rear end. Glove box has a GT4 RPO. Vin number on sticker matches truck...

I would tend to believe the RPO code. Have your dealer run the VIN to make sure!