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Author Topic: Rear Axles: How to Identify Sure-Grip And Gear Ratio  (Read 26190 times)

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Reggie

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Rear Axles: How to Identify Sure-Grip And Gear Ratio
« on: January 02, 2008, 10:29:38 »

How to Identify Sure-Grip And Gear Ratio

How To Identify A Sure Grip (Limited Slip) Differential

A limited slip differential provides better traction than an "open" type differential by automatically transferring power to the wheel that has the best contact with firm ground. Through the years, all of the major car manufacturers had their own names for the limited slip design - most notably General Motors' "Posi-Trac".  The term "Posi" has now become a generic term for limited slip differentials, regardless of the make.  Sure Grip is Chrysler's name for the limited slip differential. It was introduced as an option in 1958 with Chrysler's 8.75" axle assemblies.

Types of Sure-Grips Used By Chrysler

  • Between 1958 and 1969, Chrysler used the Dana Power-Lok design, which used clutches to provide the differential locking action.
  • From 1969 forward, Chrysler used the Borg Warner Spin Resistant design which used a spring-preloaded cone friction arrangement for the locking action. This design was later sold to Auburn Gear, so it is now usually called the Auburn style. The Auburn design was used in all M-Body 8.25" differentials that were ordered with Sure-Grip.

How To Tell If You Have A Sure-Grip

  • Check the fender tag under the hood. If it has "A38" or "AHB" listed on the tag (depending on the year), your M-body was formerly a cop car . Cop car M bodies almost always had Sure-Grip rears. If your M-body is not a former cop car, you probably have an "open" type rear and not a Sure-Grip.
  • Pull the oil fill plug. If you can see springs inside the differential carrier, it's a Sure Grip.
  • To check manually:
    • Block the front wheels.
    • On level ground, jack the rear of the car up so that the rear wheels are off the ground.
    • Put the rear of your car up on jackstands (good ones), and make sure that your car is stable.
    • Place the gear selecter in "N" for neutral.
    • Disengage the parking brake.
    • Turn one wheel and observe the other wheel.
    • If you have a Sure Grip, turning one wheel will turn the other wheel in the SAME direction.
    • If you do not have a Sure-Grip, the other wheel will turn in the OPPOSITE direction.

How To Tell What Gear Ratio You Have

To properly determine your gear ratio, you will first need to know if you have a Sure-Grip style rear or an "open" type rear.

  • Sure-Grip Differential - Both rear tires must be off the ground if you have a Sure-Grip.
    • Chalk mark a spot on the diffential housing.
    • Chalk mark the driveshaft and align it with the mark on the housing.
    • Chalk mark a wheel where it will be visible.
    • TURN THE REAR WHEEL.
    • Count the number of times the driveshaft spins for ONE revolution of the rear wheel.
    • This number (including fractions of turns) is the gear ratio.     
                                                                                 
  • Open-Style Differential - You MUST leave one rear tire on the ground if you have an open differential. 
    • On level ground, jack one side of the car so that only one rear tire is off the ground.
    • Support the raised side on a jackstand (a good one), and make sure that your car is stable.
    • Place the gear selecter in "N" for neutral.
    • Disengage the parking brake.
    • Chalk mark a spot on the diffential housing.
    • Chalk mark the driveshaft and align it with the mark on the housing.
    • Chalk mark a wheel where it will be visible.
    • TURN THE REAR WHEEL.
    • Count the number of times the driveshaft spins for every TWO revolutions of the wheel.
    • This number (including fractions of turns) is the gear ratio.

Sources:
« Last Edit: January 08, 2008, 16:05:59 by Reggie »
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