Rearend Maintenance Checkup
Gear specialist Jim Cook tears into the center section of a Ford nine-inch rear for an inspection and rebuild. Inspecting and rebuilding your rear gears should be a regular part of your maintenance routine.
Gear specialist Jim Cook tears into the center section of a Ford nine-inch rear for an ins

Recently, while visiting the shops of Jim Cook Racing Gears and Transmissions, owner and gear specialist Jim Cook showed us the center section from a Ford nine-inch rear that a racer had sent in to be checked out after it had been damaged on the racetrack. During a wreck, the panhard bar had apparently broken loose from its mount and struck the pinion cover. There is obvious damage to both the cover and the seal, and rather than risk further damage, the racer wanted the entire works checked out. Cook said it wasn't a bad idea since it was nearly time for a gear rebuild anyway, and the racer could get a little peace of mind while saving himself some money.

Of course, even if you don't damage your rear gears on the track, the entire center section should be torn down and inspected periodically as part of a regular maintenance schedule. Exactly how often depends on several factors including the length of the races generally run, the traction available at the tires, engine power and even vehicle weight. Most lowerlevel racing classes can get by with an off-season teardown if there are no problems during the season, but for touring classes with longer main events and higher-horsepower engines you may require a midseason inspection.

So, follow along with Jim as he gives this rearend the once over.

  • Rearend Maintenance Checkup
    Cook pulls the seal out of the pinion cover. You can see the damage to the seal from an on-track mishap that caused the racer to send the entire center section in for inspection.
    Cook pulls the seal out of the pinion cover. You can see the damage to the seal from an on
  • Rearend Maintenance Checkup
    This unit features an internal oil pump that circulates the gear oil to an external cooler and then directs it back onto the ring gear for maximum cooling efficiency. These are a great idea but can get costly compared to an external belt-driven pump because every center section you carry to the track must be equipped with one.
    This unit features an internal oil pump that circulates the gear oil to an external cooler
  • Rearend Maintenance Checkup
    After disassembling the pump, Cook pulls the ring gear and locker and begins separating that assembly.
    After disassembling the pump, Cook pulls the ring gear and locker and begins separating th
  • Rearend Maintenance Checkup
    The teeth of the center unloader gears must be in good condition for the locker to work properly. These still look good. General wear from extended laps will cause the edges of the teeth to round off causing erratic locker performance.
    The teeth of the center unloader gears must be in good condition for the locker to work pr
  • Rearend Maintenance Checkup
    Cook always checks the strength of the locker springs. Most racers use 75 lb. locker springs, and Cook says any time a spring has lost 15 to 20 pounds of rating it is time to replace it.
    Cook always checks the strength of the locker springs. Most racers use 75 lb. locker sprin
  • Rearend Maintenance Checkup
    Of course, most of us don't have spring checkers laying around our race shops. If you don't, Cook says a good tip is to stand your old spring beside a new one. A worn-out spring (left) compresses and will be signifi cantly shorter than a new locker spring (right).
    Of course, most of us don't have spring checkers laying around our race shops. If you don'
  • Rearend Maintenance Checkup
    After checking the ring gear for cracks or excessive heat (it turns the teeth brown or blue), you can begin reassembly of the ring gear onto the locker housing. It can be tough to get the gear centered and fl at against the housing, so Cook recommends using three bolts with nuts threaded onto them. Thread the bolts loosely into the ring gear and then turn the nuts a bit at a time to slowly pull the ring gear into position.
    After checking the ring gear for cracks or excessive heat (it turns the teeth brown or blu
  • Rearend Maintenance Checkup
    Another trick is to use a long piece of threaded rod with fl at fender washers and nuts on either side to compress the locker assembly and springs so that it can be placed into the locker housing.
    Another trick is to use a long piece of threaded rod with fl at fender washers and nuts on
  • Rearend Maintenance Checkup
    Here, with the assembly properly compressed, you can see how simple it is to drop into place.
    Here, with the assembly properly compressed, you can see how simple it is to drop into pla
  • Rearend Maintenance Checkup
    Now, you can tap the rest of the housing into place, install the ring gear bolts to hold everything together and fi nally unbolt and remove the threaded rod to unload the locker springs.
    Now, you can tap the rest of the housing into place, install the ring gear bolts to hold e
  • Rearend Maintenance Checkup
    The ring gear bolts should be torqued to 70 lb-ft, which is practically impossible to do by holding the center section in your hands. You can use a vise to hold the assembly still while torquing the bolts, just make sure to use a pair of soft jaws (either brass or aluminum) in the vise and avoid clamping against the ring gear any tighter than necessary.
    The ring gear bolts should be torqued to 70 lb-ft, which is practically impossible to do b
  • Rearend Maintenance Checkup
    You should always check to make sure the locker locks and unlocks properly before reassembling yourM center section. You can only do this by loading and unloading the gears. Cook uses the inner sections of two old axle shafts- one of which is welded to an old steering wheel. The bottom shaft holds the assembly still while he uses the upper axle to test the locker.
    You should always check to make sure the locker locks and unlocks properly before reassemb