GM Axle ratio?

[Fishin4Life]

I was looking through the manual for my towing capacity on my 98 GMC sierra that I bought recently and it goes by motor and then by axle ratio. Where does a guy go about finding the rear axle ratio?

[boatfixer]

If you do not have the original invoice, ask a GM dealer to run the vin number and they should be able to tell you, airjer would probably know about this though.

[Macgyver55]

You can manually check the ratio by jacking the rear wheels off the ground, (be safe, use jack stands etc) put a mark on the drive shaft where it is easily visible. Then turn the rear wheel exactly one turn while counting the amount of times the drive shaft turns. That will be your ratio.

Typical ratios for GMCs would probably be either 3.08..... 3.23.....3.42 or 3.73. A 3/4 ton may have a 4.10 but they arent as common.

[Fishin4Life]

Nope just bought it used and it didn't come with the original invoice. Maybe I will try that, makes sense.

Thanks!

[Valv]

Some vehicles have a tag inside glove compartment with all the accessories codes, paint code and gear ratio.

Otherwise look on the rear "pumpkin" differential bolts, there should be a tag, clean it up and that will tell you exactly the ratio

It will say 4:10 or 3:73 or 3:55 etc.

[Fishin4Life]

I checked the glove box first (easiest of course) no ratio there, I will have to check the pumpkin later on or tomorrow. If its not there I will spin the wheels and count I guess

Thanks for all the help

[Dan Thiem]

Look in the glove box like Valv said. Find the G #'s. G80= limited slip, GU2 is 3:42, I think, just guessing, I'm not at work. Just find the G#'s in the glove box and call any GM parts dept. Ask them what RPO the G numbers are. That should do it.

[Fishin4Life]

Hey thanks Dan, I found a GU6, googled it and it came up a 3.42, glad that mystery is solved. For some reason that has been bugging me. LOL