RING & PINION SETUP BASICS - MOTOR

RING & PINION SETUP BASICS

Photo courtesy West Coast Differentials

The prospect of installing and adjusting driveline ring & pinion gears can be intimidating for shops that don't routinely perform this task. Even if you farm this

work out to a specialist, you should understand what's involved.

W ith any automotive repair job, whether you're dealing with used or new components, it's critical to first clean those parts with solvent. Working with driveline ring & pinion gears is no exception. Let's get right to it.

Using a fine file, remove any burrs on the rear of the ring gear and carrier mounting surface, then clean the surfaces and housing to remove any metal particles, including any oil passages in the housing. Be sure to clean out any oil grooves adjacent to the carrier bearings. With axles removed, clean the axle tubes with solvent-soaked rags until they're absolutely clean. All seal surfaces should be inspected for imperfections. If necessary, polish seal surfaces with a fine-grit emery cloth and clean with solvent.

If you're dealing with a used ring & pinion set, whether rebuilding an existing axle assembly or installing a used set of a different ratio, inspect the back face of the ring gear for flatness. A slight taper may have occurred during heat-treating. Any taper or unevenness can be corrected by lapping the ring gear face on a flat glass plate with sandpaper or emery cloth.

Whether new or used, check the ring gear mounting surface for nicks or burrs and correct as needed to ensure a flush mounting surface.

When setting up a differential ring & pinion, the critical adjustments required include pinion depth, pinion bearing preload, gear backlash and carrier bearing preload. Go slow and pay attention to details. Expect to perform an initial test fitting and adjustment prior to final setup. As noted by West Coast Differentials (), pinion depth shims are placed either under the rear pinion race or on the pinion

shaft under the rear pinion bearing. During initial setup, try using the

original shim depth for your first attempt. The rear pinion bearing must be pressed on the pinion shaft and the pinion races must be tapped into the housing with a large punch so they seat evenly. Install the front bearing and carefully tap the pinion seal in place with a properly sized seal driver or an old race. West Coast Differentials notes that Ford 8- and 9-in., and GM 10.5- and 12.25-in. ring gears use a pilot bearing that must be tapped in, with a retainer for the Fords. Mount the ring gear to

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Jim Gibson

VDO - A Trademark of the Continental Corporation Illustration courtesy Richmond Gear

the carrier with a drop of red (highstrength) threadlocking compound on each bolt. Carrier bearings are pressed on the carrier and secured with green Loctite. Note that in Dana Spicer differentials, the carrier shims are located between the carrier and carrier bearings.

It's important to note that pinion bearing preload is always measured in inch-pounds at the pinion nut, so a quality, calibrated inch-pound beamor dial-type torque wrench is needed. Be sure to apply clean oil to the pinion nut washer surface during all assemblies and high-strength threadlocking compound (for example, red Loctite) on the pinion nut threads during the final assembly (not during initial test fitting).

Some designs feature a crush sleeve for setting pinion depth, while others require the use of preload shims. If the design calls for the use of a crush sleeve, it may be easier to initially install the pinion without a crush sleeve until the correct pinion depth

has been established. Always use a new crush sleeve for final assembly.

When installing a crush sleeve, slide the sleeve onto the pinion shaft and install the pinion through the rear of the housing. According to West Coast Differentials, the yoke usually must be tapped on while you apply pressure on the pinion gear head to hold it in place. Use an impact wrench or huge breaker bar to apply the torque necessary to crush the sleeve. Proceed very slowly so so as not to overload the bearings. The pinion preload will be zero until the bearings contact the races but will then increase very quickly. Again, use an inch-pound torque wrench to check the preload. If the pinion bearing preload exceeds the specified allowable range, install another new crush sleeve and start over. If the design calls for a crush sleeve, it's a good idea to keep a handful of these sleeves handy during test-fitting.

If preload setting requires the use of shims instead of a crush sleeve,

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Drive

Heel Coast

Toe

On a ring gear, the outboard area is referred to as the heel, while the inboard area is the toe. The drive side receives the push-force from the pinion gear. The shaded areas depict an ideal wear pattern.

first carefully clean the shims to remove any particles that may cause a false preload reading or cause the shim stack to change thickness over time as the vehicle is driven. Maintain a clean surface on your workbench while organizing shims to prevent contamination.

Slide the shim pack over the pinion shaft to the shelf. West Coast recommends using the original shims on the first assembly, or adding .003 in. to the original preload shims to make up for the bearings settling into the housing.

Gradually tighten the pinion nut in increments to a final value of approximately 250 ft.-lbs. Recheck preload with an inch-pound torque wrench as you go, between nut-tightening increments, to avoid damaging the bearing. (Don't immediately tighten to full value, and keep rechecking preload.) If the preload is too tight, remove the pinion gear and add shims so the bearings will not be as tight against the races. If the preload is too loose, remove shims so that the bearings will be tighter against the races and increase the preload.

Once you've achieved the proper preload, lightly tap both ends of the pinion to seat the bearings, races and yoke. Once the pinion has been seated, recheck the pinion preload with your inch-pound torque wrench.

Insufficient carrier bearing preload allows the carrier to move when under load; this can cause the back-

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Illustration courtesy Richmond Gear

Checking Distance

2.468

Place Shims Needed to Get to the Required Pinion Depth in These Locations

Checking Distance

Place Shims Needed to Get to the Required Pinion Depth Between Bearing Support & Housing

These are examples of the checking distance between the axle centerline and the pinion on typical GM and Chrysler applications (left) and on Ford 9-in. applications (right).

lash to open up. West Coast notes that carrier bearing preload is not specifically measured, but a good, tight fit is important in all differential designs. Backlash is measured by mounting a dial indicator to the housing with the plunger set perpendicular to the ring gear teeth. While holding the pinion yoke steady, rotate the ring gear back and forth. Backlash will generally change about .007 in. for each .010 in. the carrier is moved. To decrease the backlash, move the carrier closer to the pinion centerline; to increase the backlash, move the carrier away from the pinion centerline. Backlash may be adjusted by threaded adjusters or with the use of shims, depending on the design.

Typically, backlash for a street application will be in the .007- to .009in. range. The backlash adjustment for GM and Dana applications is typically accomplished with the use of shims placed behind the carrier bearing cups.

Once the gears are initially installed, paint the pinion gear teeth with a gear-marking compound or machinist's dye to check gear-to-gear tooth contact patterns. Rotate the ring gear several times by hand and inspect the ring gear teeth. If the witness pattern shows heavy on the "toe" (inboard area of the ring gear), subtract shims. If the pattern is heavy on the "heel" (outboard area of the ring gear teeth), add shims. Ideally, the contact pattern should be seen in the

middle area of the teeth. Resetting the pinion depth may be necessary as well.

If the carrier features a threaded screw adjuster design, first lube the adjuster threads with oil on both the housing and the adjusters. While holding the races on the bearings, place the carrier in the housing. Install the carrier caps according to the marks made during disassembly so the threads are seated evenly on the adjusters. Note that third-member differential designs require a 10- to 12-in. spanner wrench to tighten the adjusters. West Coast notes that Chrysler differential designs require an extension bar and special spanner to access the adjusters through the axle tubes. Tighten both the left and right adjusters evenly by hand until they're fairly tight. If the backlash is excessive, tighten the left adjuster until the backlash is correct; if the backlash is too tight, tighten the right adjuster until the backlash is correct. If necessary, loosen one adjuster and tighten the opposite adjuster. Once the desired backlash has been achieved, both adjusters must be fully hand-tightened. The final adjustment requires tightening the left adjuster, since the ring gear is forced away from the pinion gear while under load.

Differentials that require shims may need them between the carrier bearing races and the housing,

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Illustrations courtesy West Coast Differentials

Too Deep

Heel

Coast

Heel

Coast

Too Shallow

Heel

Coast

Heel

Coast

Drive

Toe Drive

Toe Drive

Toe Drive

Toe

Acceptable

Heel

Coast

Heel

Coast

Drive

Toe Drive

Toe

Heel

Coast

Toe Drive

Heel

Coast

Heel

Coast

Heel

Coast

Heel

Drive

Toe Drive

Toe Drive

Drive Toe

Coast

Heel

Coast

Toe

Drive

Toe

Heel

Coast

Heel

Coast

Heel

Coast

Heel

Coast

Heel

Coast

Heel

Coast

Drive

Toe Drive

Toe Drive

Toe Drive

Toe

Drive

Toe

Drive

Toe

The ring & pinion gear contact wear patterns shown on the left indicate that the pinion was adjusted too deep. The patterns in the center indicate that the pinion was adjusted too shallow. Acceptable wear patterns are shown on the right. The ideal pattern is seen in the top two examples on the right.

or between the carrier bearing and of the shims. The carrier should be the carrier case. Carrier bearing pre- shimmed tight enough that it must load is established by the tightness be tapped in with a plastic dead-blow

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hammer. While holding the races on the bearings, and with outer shims on the races, start the carrier into the housing and tap it in with the hammer. Install the carrier caps according to the marks made during disassembly. Measure the backlash. If it's excessive, move or add shims to the left side. If the backlash is too tight, move or add shims to the right side. If the carrier is too tight or too loose, remove or add shims as needed.

The pinion depth specification (measured from the pinion face to the axle centerline) should be marked

Photo courtesy West Coast Differentials

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A new ring & pinion set can be damaged quickly--as this one was--if adjustments and/or lubrication aren't correct.

on the face of the pinion and must be set, staying within .002 in. of the specification. Depending on the style of the assembly, either a crush collar or shims can be used to adjust pinion depth. Once the pinion depth has been set, pinion preload must be applied while rotating the pinion. For used bearings, set preload at 15 in.-lbs.; with new bearings, set preload with 25 in.-lbs. Once preload has been set, install the pinion seal and the pinion locking nut (apply red Loctite high-strength locking compound or equivalent). With the pinion gear installed, position the ring gear and carrier into the housing and inspect gear backlash.

Never mix & match ring gears and pinion gears. These are made as sets, and gears are lapped as a set. Inspect each gear to verify that the serial numbers match.

Always apply a coat of gear oil on all bearings and grease on all seals

Photo courtesy West Coast Differentials

Inadequate lubrication resulted in a severe overheating condition, as evidenced by this example of a badly burned ring & pinion set.

and seal surfaces just prior to installation. Refer to the gear maker's lubricant recommendation; generally, a synthetic 75W-140 gear lube should be correct. If the differential is a pos-

itraction/limited slip design, a friction modifier will be required in addition to the gear lube. The amount of friction modifier can vary depending on the application, but generally somewhere between 4 and 8 oz. should suffice. If a friction modifier is not added to the lube when required, driveline chatter may occur (as a result of clutches sticking), possibly most notably in Reverse with the steering wheel turned.

For street operation, with gears sets of 3.73 or lower (3.73 or higher numerical ratio) it's recommended to drive the vehicle for about 500 miles at varying speeds. Avoid constant cruising in one speed range.

Thanks to West Coast Differentials and Richmond Gear for their assistance with this article.

This article can be found online at .

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