74 Duster - I want new gears! 3.91

Sure Grip is the Mopar name for a LSD (Limited Slip Differential). Also known as a "Posi" by the great unwashed.

Simply stated, limited slip diffs apply drive to both rear wheels. This is advantageous in that you get better grip and make pretty parallel stripes on the tarmac under heavy acceleration :). The Sure Grip diff was normally an extra cost option back in the day. The 8 3/4 was available as a Sure Grip or a "single spinner".

To determine what you have, jack up the rear end, put the car in neutral and spin a rear wheel by hand. If both rear wheels turn in the same direction, you have a Sure Grip. If the two wheels turn in opposite directions, you don't.