Differential Drive Pinion and Drive Gear


There are two types of carriers used in differentials: the removable carrier and the integrated carrier. The procedure for replacing the ring and pinion gears (or drive gear) is similar for each type. Remember, to service an integrated house usually requires that a case spreader must be installed on the differential housing.

After the ring and pinion gears have been inspected and before they have been removed from the differential assembly, check the side play. Using a screwdriver, attempt to move the differential case assembly laterally. Any movement is evidence of side play. Side play normally indicates that as the result of loose bearing cones on the differential case hubs, the differential case must be replaced.

After removing the differential from the housing and prior to disassembling the differential assembly, measure the runout of the ring gear. excessive runout can be caused by a warped gear, worn differential side bearings, warped differential case, or particles trapped between the gear and the case.

  • Runout is checked with a dial indicator mounted on the carrier assembly.
  • The plunger on the indicator should be set at a right angle to the gear.
  • With the dial indicator in position and its dial set to zero, rotate the ring gear and note the highest and lowest readings. The difference between these two readings indicates the total runout of the ring gear. Normally, the maximum permissible runout is 0.003 to 0.004 inches (0.0762 to 0.1016 mm).
  • To determine if the runout is caused by a damaged differential case, remove the ring gear and measure the runout of the ring gear mounting surface on the differential case.
    • Runout should not exceed 0.004 inch (0.1016 mm).
    • If the runout is greater than that, the case should be replaced.
    • If the runout is within specifications, the ring gear is probably warped and should be replaced.

Replacement Procedure

  • A ring gear is never replaced without replacing its mating pinion gear. If one gear is damaged, they must both be replaced.
  • On some types of differentials, the drive pinion gear can be removed by unbolting it from the housing. On other types, the pinion nut and flange are removed.
  • After the pinion gear is removed from the housing, check the pinion bearing.
  • Ring gears are bolted to the differential case.
    • Some ring gear assemblies have an excitor ring, used in antilock brake systems. This ring is normally pressed onto the ring gear hub and can be removed. If the ring gear assembly is equipped with an excitor ring, carefully inspect it and replace if it is damaged.
    • When installing a ring gear into the differential case, make sure the bolt hole are aligned before pressing the gear into place. Pilot studs made from cutoff screws with a hacksaw slot for a screwdriver are a good idea.
Pilot studs assist in installation of a ring gear.
    • If a ring gear is being replaced, it can be heated in oil to make it easier to install on the case.
    • The ring gear must be installed perfectly flat. While pressing the gear, pressure should be evenly applied. Likewise, when tightening the bolts, always tighten them in steps and to the specified torque. These steps reduce the chances of distorting the gear.
Torque the ring gear screws.
  • Before reassembling any components in the differential:
    • Clean all parts in solvent and blow them dry.
    • Coat all parts with differential oil prior to assembly.
  • During reinstallation, examine the gears to locate any timing marks on the gearset that indicate where the gears were lapped by the manufacturer.
    • Normally, one tooth of pinion gear is grooved and painted, while the ring gear has a notch between two painted teeth. If the paint marks are not evident, locate the notches.
    • Proper timing of gears is set by placing the grooved pinion tooth between the two marked ring gear teeth.
    • Some gearsets have no timing marks. These gears are hunting and do not need to be timed. Non-hunting and partial non-hunting gears must be timed.
  • Adjust the pinion bearing preload and the pinion gear depth, gear backlash and gearset patterns.