Gear specialist Jim Cook tears...
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.
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.
Cook pulls the seal out of...
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.
This unit features an internal...
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.
After disassembling the pump,...
After disassembling the pump, Cook pulls the ring gear and locker and begins separating that assembly.
The teeth of the center unloader...
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.
Cook always checks the strength...
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.
Of course, most of us don't...
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).
After checking the ring gear...
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.
Another trick is to use a...
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.
Here, with the assembly properly...
Here, with the assembly properly compressed, you can see how simple it is to drop into place.
Now, you can tap the rest...
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.
The ring gear bolts should...
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.
You should always check to...
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.
As long as the pinion gear...
As long as the pinion gear and its bearing look good, it can be reused. If that is the case, not removing the shims and crush sleeve should ensure the pinion depth will still be correct. Of course, don't forget to check the bearing race inside the front cover. It should be free of scratches, gouges and heat marks.
Don't forget that even if...
Don't forget that even if you use an oil pump to cool and move lubricant around in your rearend, it doesn't work until the car starts moving. Protect the bearings with a liberal coating of white lithium grease.
They may be more expensive,...
They may be more expensive, but Cook recommends using a quality Viton pinion seal to minimize leaks.
The internal oil pump is actually...
The internal oil pump is actually driven off of the pinion gear. It requires a special pinion with a hex cut into the end of it, and the pump's driveshaft slots into the end of it. Cook says he purchases his pumps and pinions from G-Force South in Asheboro, N.C.
Be careful when installing...
Be careful when installing the spanner nuts so that they do not get cross threaded in the housing.
Cook says he tightens the...
Cook says he tightens the spanner nuts while turning the ring gear until he starts to feel some drag and then backs off a bit, which should at least get you close to the correct backlash. After that, you can use the spanner nuts to move the carrier laterally to increase or decrease backlash.
Backlash should be checked...
Backlash should be checked in at least four places around the ring gear with a dial indicator. With the pinion gear held steady, you should have between 0.008 and 0.010 of play in the ring gear. If your backlash changes signifi cantly at different parts of the ring gear, that's a sign that the ring gear isn't seated snugly to the carrier all the way around.
Once your backlash is correct,...
Once your backlash is correct, paint a section of teeth with gear paint and spin the gears several times to check the pattern. Use a rag and squeeze the pinion shaft while spinning the ring gear to provide some resistance-this will provide a more accurate pattern.
Cook finishes assembly of...
Cook finishes assembly of the oil pump. He says that unless trash somehow gets into the system he rarely sees any real wear in these types of pumps.
The last step before buttoning...
The last step before buttoning everything up is to wire-tie the bolts. This is definitely a step not to be overlooked because once the center section is installed in the rearend, it's impossible to check and make sure vibrations haven't caused the bolts to loosen.
Your pattern should show the...
Your pattern should show the gears mesh on the bottom portion of the ring gear teeth. This is different from a passenger car where you would normally want the pattern to be centered, but in a high-horsepower racecar, the extra horsepower will push the pattern toward the center in real-world use.