Re: Rear end with Ultramatic

Posted by Eric Boyle On 2008/7/14 1:06:41

Simple procedure for determining rear axle ratio: jack up the entire rear end of the car, so that both wheels are off the ground. (Making sure the car is out of gear and the front wheels are chocked so the car cannot move) Now, turn the rear wheel so the valve stem so it's on the bottom. This is where a helper will come in, take a piece of chalk and mark the driveshaft with a line that you can see easily. Have a friend turn the wheel ONE revolution forward, and watch the driveshaft, counting the turns. It will most certainly end up past 3 or 4 turns, so you'll have to do an "educated guess" here. If it turns 3 and a half times, you have a 3.54 gear ratio. If it turns a little over 4, it's a 4.10. A simple, but effective way of determining gear ratio. As always, be very careful while under a lifted car, as anything can happen at any moment.

This is all a "gear ratio" is, how many turns the driveshaft makes per one revolution of the wheel.

If I remember correctly, if it's an open differential (non-positrac) you only need ONE wheel off the ground.