How To Find The Gear Ratio Of A Rear End

How To: Decide the Rear Axle Ratio

How To: Determine the Rear Axle Ratio

Rear Axle Ratio

The rear axle ratio of your car is instrumental in determining which transmission gear set is best suited for your car. It is also important to know the ratio every bit well as tire size to make up one's mind which speedometer gear y'all need and so your speedometer reads accurately. By following these directions, you lot can make up one's mind what the axle ratio is in your machine.

Determining a Rear Axle Ratio of a Posi Rear

Rubber kickoff! Chock the front tires and then your car won't slide off the jack stands and so raise the rear of the car with a hydraulic flooring jack and place heavy duty jack stands on either side of the rear beam housing. Lower the car onto the jack stands.
Turn the commuter'southward side tire a quarter plough counterclockwise to remove the slack in the drivetrain.
With a piece of chalk or masking (painters) tape make about a 6" line along the driveshaft that can be easily seen from the side of the car and make another mark on the tire. It's good to make this mark in a place that is easy to line up, like the edge of the wheel well or the 12 o'clock position.
Rotate the tire counterclockwise while counting the number of times the driveshaft rotates until the tire has completed one complete turn. (You may need a helper if you can't rotate the tire and run into the driveshaft at the same time.) Be as accurate equally possible.
The number of driveshaft rotations will help you lot determine your rear axle ratio. For instance, if it turned 3 and a half times, it's a 3.50:1 ratio. If information technology turned iv and a quarter times, it'due south a four.25:1 ratio.
Remove the tape/marks from the driveshaft and tire, heighten the rear tires over again and remove the jack stands before lowering your car back to the ground. Remove the chocks from the front tires.

Determining a Rear Axle Ratio of a Non-Posi Rear

Jack ane wheel off the ground, put the transmission in neutral and take the parking break off. ***Be certain to use jack stands nether the axle for prophylactic precaution***
Mark the bicycle and the drive shaft with chalk or masking tape.
Plow the wheel TWO revolutions and count the number of driveshaft turns.
The number of driveshaft rotations volition aid you decide your rear beam ratio. For example, if it turned three and a half times, information technology'due south a iii.l:1 ratio. If it turned 4 and a quarter times, it's a 4.25:one ratio.
For meliorate accuracy, turn the wheel 20 times and divide by 2 for your rear axle ratio.

If yous are unsure whether you take a Posi Rear or not

Jack both wheels off the basis and turn one wheel.

If the opposite wheel turns the same direction or doesn't turn at all, then the rear axle is posi or express slip.
If the opposite cycle turns the opposite management, then it'due south probably an open up rear beam (non-posi).