How to Determine the Axle Ratio in a Dodge Ramby Don Bowman
When determining the axle ratio in a Dodge Ram for the purpose of changing to a different ratio, several things should be considered. On newer vehicles, the shift points in the transmission, the speedometer and the cruising rpm will change accordingly. On four-wheel-drive vehicles, both the front and rear ratio must agree. The higher the number of the ratio, the lower the gearing. For instance, a 4:11 gear means the driveshaft will turn 4:11 times for every revolution of the tire. Conversely a 3:50 will turn three and a half turns to every revolution. A high number will give more acceleration and less top end, with the reverse for a smaller gear.
Look on the rear axle carrier housing for a metal tag with the gear ratio stamped on it. In lieu of a tag, proceed to the next step.
Raise and support the truck on jack stands. Place the drive pan under the carrier housing cover. Remove all the 13mm bolts in the cover on the housing, using a socket.
Pry the cover off slowly from the bottom, pausing to allow the gear oil to flow into the drain pan slowly. Put the transmission in neutral.
Rotate the tire while counting the number of teeth in the large ring gear. Do the same for the small pinion gear in the front of the ring gear. Divide the smaller number into the larger number. This is the gear ratio.
Clean the gasket off the cover with the gasket scraper. Use a clean cloth to clean the sealing out edge of the cover. Place a bead of RTV sealant around the outside circumference of the cover in the sealing area. Allow the RTV to dry until it skins over enough that it can be touched lightly without sticking to a finger.
Install the cover and the 13mm bolts and tighten. Fill the carrier with gear oil through the access plug on the side. It will be full when the gear lube begins to run back out of the access hole.
Things You'll Need
- Floor jack
- Jack stands
- 3/8-inch drive ratchet
- 13mm socket
- Drip pan
- Two quarts of gear oil
- One tube of RTV silicone sealant
- Clean rags
- Gasket scraper
- Common screwdriver
Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).