How do I figure out what gear ratio I have?

[JFerg65]

Got this new 96 2500 suburban, well... used, how do I go about figuring out what gears I am running? Bolt pattern, vin code??

Any help would be appreciated. The only gear work I've ever done is replacing the pumpkin in a 1952 Dodge M37 military power wagon.

[DmaxMaverick]

Since you aren't the original owner, you can't rely on the RPO code (code list on a sticker in the glovebox).

If it has an open or locking diff (not limited slip, which would not be OEM for 1996), jack up one rear wheel (chock the other, and fronts). E-brake off and out of P, rotate the rear wheel exactly 2 full turns, and count the turns of the driveshaft (mark it with chalk, crayon or paint). The shaft turns will be the gear ratio. I don't think the 2500 Suburban was available with a higher gear than 3.73, but you should be able to calculate it if it's been changed, or I'm wrong.

[JFerg65]

Thanks so much!
I printed off the codes from the sight, went to my glove box and there it was!! I'm confident nothing in the drive train had been altered, since this was a fire department vehichle maintained through a county fleet managament system.

So I have 4:10 gears in the 2500. I've read that the 16 -17 I'm getting is all I'm gonna get, that is not good news. I really wanted to turn this into the 20+ MPG Suburban.

I'm I correct in assuming trying to switch out the gears will not be cost effective over time? I have read others running with 4:10's and others, also experience similar mileage. I know this has a lot more life in her considering she's only got 137,000 and change under her belt. I think I'll save for the starter upgrades, exhaust etc..

Thanks for the help

[DmaxMaverick]

Unfortunately, the ROI on gear changes are rarely good....and you give up performance. Unless you need to get rid of annoying highway engine screaming, there's really no gain. The engine is happy running the higher RPMs, so still, no gain.

[JFerg65]

Thanks for the confirmation! I can't begin to tell you how great this forum is!!! I really do appreciate all the answers to questions I've had so far. It definately assisting in keeping keeping my learning curve with my first diesel not quite as steep as I though it was going to be.

So, the 4:10s will remain, and on to the next project.

[Shikaroka]

My Suburban has 4:10s as well. I like to drive 70 and it's a bit loud for me at those RPMs. I've got a set of 3:73s that I plan on putting in, I just haven't had the time yet. I'm hoping to get a little more MPGs as well as tone her down some on the highway. Plus I figure, less RPMs may help the longevity of the motor a little.
I think if you can do the work yourself, it's not too costly.

[JFerg65]

let me know how the swap goes and what kind of results you get

[Shikaroka]

Sure thing.
I hope to get it done this summer. Hopefully by the end of July.