by Larry Shepard
(Taken from Jeep, Dana & Chrysler Differentials: How to Rebuild the 8-1/4, 8-3/4, Dana 44 & 60 & AMC 20)
The biggest advantage of the basic Sure-Grip or limited-slip in acceleration situations or racing applications is that it divides the available power/torque between the two rear wheels. This allows more power and/or torque to be put to the ground and used to accelerate the vehicle harder and quicker whether cornering or going in a straight line.
One of the first steps in using a rear-wheel-drive vehicle in acceleration contests or racing is to determine whether it has a Sure-Grip. If it does, the next step is to determine if the Sure-Grip that you have is still good. Sure-Grips do wear out.
The simple test for a Sure-Grip versus limited-slip differential is as follows:
• Jack up the rear end of the car and support it on jack stands. Both wheels must be off the ground. Confirm that the parking brake is off and that the transmission is in neutral.
• Position yourself so you can see both rear wheels/tires at the same time (under the car), near the ground, ahead or behind the tire. The routing of the exhaust pipe has a lot to do with the best location.
• Rotate the left-side tire counterclockwise.
• If the right-side tire rotates in the same direction, this indicates a limited-slip differential. The following is a more detailed test for the correct installation and function of the standard-type limited-slip differential. Remember that this procedure may not work for lockers and spools.
• Raise the rear axle off the floor, so that both tires are completely off the ground. Support the rear on jack-stands. Double-check that the parking brake is off.
• With engine off, place the transmission in park (automatic) or first gear (manual).
• Grip the tire with both hands and try to rotate the tire/wheel (in either direction). Consider using gloves.
• If you find that it is extremely difficult or impossible to manually turn either wheel, the limited-slip differential is operating properly.
• If you find that it is relatively easy to continuously turn either wheel, it means the differential is not performing properly and should be removed, replaced, or rebuilt.
Jack up the rear of the car and support it on jack stands. With the engine off, and the parking brake off, try to rotate the wheels. Use both hands.