How do I determine what my rear end ratio is? I suspect that mine is 3.55, but how can I find out for sure?

 

There should be an option sticker on the underside of the hood that has the differential options for what rear end (yours should be Dana 80) and what ratio. Odds are you have 4.10's. There might also be a tag on one of the cover bolts that has the ratio on it. Otherwise you can always pull the cover off and count teeth on the ring and pinion gears, then divide the big by the little. Also, with 4.10's you will run about 2000 rpm's at 60mph

 

check the rear diff cover on the top left corner, thats where mine has it imprinted on.

 

Pop the hood and look at the tag pasted to the underside of the hood, it shows all drivetrain build options including the gear ratio.

That should be it unless the truck has had the hood replaced or someone jacked with the rear.

 

My 97 2500 4x4 automatic does not say what ratio it has on the sticker and unfortunately for me I didn't do my research before purchase and I ended up with 4.10's. (I really, really wanted the 3.55's) I thought that if it had 4.10's it would have said so on the sticker because most of the ones I had seen did - but mine didn't. My tires are 265's and I run just above 2000 rpms at 65 mph.

 

You can also request a copy of the build sheet from Dodge and they will email it to you within a day or two. That is how I confirmed that my truck did indeed have the 4.10's and other things.

 

I couldn't find a sticker on mine, but I just drove it and it turns about 1800 RPM at 60. It seems like it also turns 2000 RPM at 65. Being a dually, it probably has the 4.10 rear end. I once went to a Dodge dealership and they had the whole history of my truck (where it was bought, recall bulletins, etc) in the computer. I could probably give them the VIN number I find out.

 

My 92 turns ~2050 at 70, so you may well have 3.54s.

One other way to tell is to jack up the rear end and mark (or just make a note of) the pinion yoke and tire. Turn the wheels til you get one full turn of each wheel, keeping track of how many times the yoke turns. If it turns 3-1/2times, you have 3.54s; a little over 4x, and you have 4.10s. You will likely need a helper or monkey arms if you have an open diff- turn one wheel and the other wheel turns the opposite way, leaving the pinion stationary.

Daniel