How-to: AAM 11.5" GM Axle Rebuild and
Ring-and-Pinion Gear Change
American Axle & Manufacturing ("AAM") builds OEM
axles for Chevrolet and GMC trucks and Dodge Ram. The magazine's own '05 Ram 3500 4WD came with an AAM 11.5" rear
axle and an AAM 9.25" front axle. This article is the change to a 4.56:1 axle ratio and applies to both GM and
Dodge Ram AAM 11.5" axle assemblies. Differentials and brake assemblies may vary; however, overall axle and
differential service procedures remain largely the same. Use a model-specific shop manual as a reference
to 35" diameter tires left our Dodge Ram 3500's original 3.73:1 axle gears lacking. Too tall gearing for the
new BFG tires, plus an added 1,100 pounds of utility accessories during the Ram's
"makeover", the truck needed remedy. Boosting engine power was a possible solution.
A change to 4.56:1 ring-and-pinion sets made
better sense for our planned trailer pulling.
AAM axle gearsets are available from several sources. For quality
components, we turned to Superior Axle & Gear for reliability and a "kit" approach. The package consisted of
two ring-and-pinion matching sets (11.5" for the rear, 9.25" for the front) plus Timken bearing sets, new ring gear
bolts, preload shims, crush sleeves, seals, sealants, thread locker, tooth contact paint, and a pinion nut for
For those familiar with Dana integral axles, the AAM approach is a
departure, especially the differential carrier removal and installation. In some ways, the AAM is quicker to set up
than the Dana units. However, like every axle type, the critical, adjustments remain the same and in this
sequence: 1) pinion depth into the housing, 2) pinion bearing preload, 3) differential/ring gear backlash, and 4)
carrier bearing preload.
The right tools are an important part of an axle builds. The
AAM units require some specialty tools. In this step-by-step coverage of the ring-and-pinion gearset change, tools
play an important part. Some tools are inexpensive, others can be
improvised—a few will require willingness to invest in
From this how-to coverage, determine whether rebuildng
your own axles matches your skill level and tool budget. Whether this is a one-time task or
your professional work, the steps described will serve as a guide for these critical
Skill level required: Familiarity with gear mechanisms and ability to follow technical
Needed tooling: Specialty tools required—review the steps before taking on this kind of
Step 1: Use wheel chocks to prevent vehicle
from rolling! Once jacked up on a slope, the vehicle will roll whether in Park, gear or even with the E-brake
Step 2: Always use a quality set of jack stands
and a rated floor jack. Our Dodge Ram 3500 is now over 8900 pounds curb weight. These Walker stands rate
5-tons apiece. Pittsburgh floor jack rating is 4-tons. Both work well and provide a safety
Step 3: At 5-tons apiece, the load capacity of
these two stands is 10-tons. Note placement at base of axle tubes, between spring U-bolts, away from brake
tubing. Tires are just off the ground and can be removed readily.
Step 4: Ram 3500 has a full-floating rear axle.
This makes differential work much easier. Axle shafts are quickly removable, rotors and calipers can stay in
Step 5: Drain the axle oil into a clean pan.
Inspect for metal and debris. You will wipe out the differential cavity with clean, lint-free rags. Properly
maintained oil on the Ram 3500 is clean and free of contaminants.
Step 6: OEM 3.73 gears worked for 100K miles
just fine—right up to the switch to 35" diameter tires, a 3-inch diameter increase. 4.10:1 would be a direct
correction for the tire size increase. 4.56:1 meets plans for trailer pulling—plus the added weight of
accessories and auxiliary fuel.
Step 7: Superior Axle & Gear's 4.56:1 ring-and-pinion
gearset is a precise, durable design. We selected 4.56:1 based on research from Cummins and our
trailering needs. With 35" tires, 4.10:1 is the direct equivalent to the OEM 3.73 gearing with the original
Note: If you have bigger diameter tires in mind and are pleased
with your truck's performance with the stock size tires, simply restore the ratio and offset the
speedometer error. For our Ram 3500, a 3.73 to 4.10 change would accomplish this...We went a step further to
meet heavier towing needs.
Footnote: The 4.56:1 gears require a speedometer
correction. Also, the engine now operates at higher cruise speed (actually closer to Cummins' own rpm
recommendations for the ISB diesel engines). Be prudent here, especially with a diesel engine. Unless you
have a distinct need for lower (numerically higher) axle gearing, don't go any lower (numerically higher)
than a restorative ratio!
To learn more about how we made our gear ratio choice, click
Step 8: Full-floating rear axle shafts are easy
to remove: begin by removing the eight flange bolts. Unless there is a threaded relief hole, use a
wedge-shaped, broad chisel to separate the axle shaft flange from the hub.
Caution: Do not
damage the metal! You are merely spreading these parts at the gasket, not chiseling or nicking
Step 9: Axle shaft removed, the hub, spindle
and wheel bearings are visible. Note that there is no mark where the chisel separated the axle shaft from the
hub. Axle shaft and hub have been indexed with yellow metal marker for alignment at reassembly
Step 10: Virtues of full-floating axle are
clear. Vehicle will actually roll with shafts removed. (Note: Oil will leak
out!) This is a distinct safety advantage over a semi-floating axle. Time-honored, heavier
duty truck design provides ease of service. Differential assembly can now be
Step 11: Spring locks keep the differential
bearing preload nuts from rotating. Remove these bolts and springs to make adjustments or remove the
Step 12: Loosen opposite retainer bolt and
spring lock. Note the relationship of these parts for reassembly.
Step 13: Bearing caps are machined match for
the axle housing saddles. To maintain precise fit, you must install caps in correct position—with the caps
facing the right way! Here, one light pin mark at the left cap and housing indicate the cap alignment for the
left bearing cap.
Step 14: Right bearing cap gets two pin marks.
Note that the marks should indicate which side and how the cap faces top-to-bottom. Axle housing gets a
matching pair of pin marks.
Step 15: Bearing caps marked, you can now
loosen the bearing cap bolts. Do not remove bolts until you can safely support the heavy differential carrier
and ring gear!
Step 16: Remove bearing cap bolts. Rock cap
slightly to loosen if necessary. Do not distort the cap or mar the cap-to-housing. This is a precise,
machined fit. Protect the caps.
Caution: As a precaution, leave bearing caps in
place if the adjusters do not securely hold the differential in place! Badly worn bearings or mis-adjusted
spanner nuts can allow the differential to roll out of the housing once the caps are
Warning: The 11.5" differential carrier and ring
gear are heavy and can cause severe physical injury if not supported during
Step 17: In this case, the bearing adjusters
were tight with preload. Do not allow the differential to roll out of the
housing. Leave bearing caps in place with bolts "finger tight", loose enough to permit
backing off the adjusters. To avoid parts damage, do not let the toothed toner ring drop onto the
Step 18: Right side spanner nut is still tight.
The marring of the holes is actually "factory"; the axle has never been apart. While some use a punch with a
blunt, rounded nose end to tap the adjuster rings loose, there is a factory service tool for the task.
Step 19: At top is Miller-SPX #8883A Tool, the official tool for the adjuster nuts
on AAM 9.25", 10.5" and 11.5" Chrysler, Dodge and Ram axles. Bottom is our "homemade" tool. (See details on fabricating a tool like
this one.) If you want to do this job correctly, consider purchasing the Miller tool
or the equivalent tool for GM axles.
The Preload Adjuster Nut Dilemma
The Miller-SPX #8883A
Tool is available at the SPX website. Note cautions on the tool like "Do not use for removal".
Miller-SPX tool is high quality and well designed for this difficult application—as you will quickly
AAM's 11.5" axle design creates decreasing notch exposure as the adjuster rings
thread into the axle housing. This requires a thinner tool, one not capable of handling excessive force. If
the AAM axle adjuster notches were fully exposed over the range of adjustment, a thicker, stronger tool
design would be possible.
Our Ram 3500 AAM 11.5"
differential preload nuts did loosen within the torque limits for this tool. There are occasions, however, when an
overly tight nut adjustment, binding spanner nuts or axle exposure to heat can increase the torque
resistance...Use prudence here!
Footnote: In a phone call to the Miller-SPX tech line, tech staff acknowledged the challenges
of this spanner nut design. The alloy steel SPX tool will take considerable load before its small notch tab
fails. As a precaution, the staff suggested the use of a blunt, rounded end punch and hammer to break initial
torque on an overly tight adjuster nut. Your call...If you do use a punch, do not damage the adjuster rings!
Vacuum away any metal debris from the axle cavity and all gear parts.
Step 20: Bearing adjusters are right-hand
thread and loosen into the axle housing. Fine housing threads must be handled carefully. Back off adjusters
carefully and be ready to catch a heavy 11.5" ring gear and differential assembly!
Caution: A support platform—like a transmission jack—is helpful...Support the differential
assembly to prevent damaging the tone ring teeth. A block of wood beneath the tone ring will prevent teeth
from dragging or banging against the axle housing as you roll the differential assembly from the bearing
saddles. Avoid pinching or crushing your fingers. If an assistant is nearby, ask for
Step 21: Big enough? 9.25" is more like a Dana
44 or AMC Model 20 unit. This is the 11.5" that can tow a nine-horse trailer and handle dual wheels and a
Caution: To avoid severe injury, don't get pinned beneath
this differential and ring gear assembly. Use a transmission jack—and strap the safety chain,
Step 22: The 3.73:1 pinion gear remains in
place. Mark and remove the threaded bearing adjusters. You will want to clean and oil them to assure smooth
adjustment during differential installation.
Step 23: Bearing cups fit precisely into the
housing saddles. Adjusters thread into the axle housing at each side. These parts must be clean for proper
fit and accurate adjustments.
Step 24: Mark the adjusters with pin punch for
proper location on reassembly. You can use this tapered tool to loosen the adjuster ring from the axle
housing. The rings should rotate freely if threads are not damaged.
Step 25: Loosen and remove all ring gear bolts.
These bolts may be extremely tight due to factory thread locker (equivalent to Loctite 271 High Strength
red). A high-torque air wrench and moderate heat (500 degrees F maximum) may be required to loosen
Step 26: Unless there is an issue, the ring
gear can be removed by tapping four loosened bolts at opposite positions on the carrier. Light taps in
sequence will prevent the gear from binding on the carrier. Do not strike or damage the carrier
Note: Presumably, the ring gear and bolts will be replaced. If reusing the ring
gear, use caution: Do not damage the threads. Tap with a brass punch at the beveled edge of the
Step 27: Ring gear dropped off uniformly and
quickly. Note the factory sealant, powdered on the gear threads. This created strong resistance when removing
the bolts. Tone ring can stay in place. Leave the tone ring-to-carrier screws tight.
Step 28: Observe the original tooth contact
pattern. This OEM 3.73 ring gear worked just fine and shows a distinct and correct tooth contact. If correct,
try to emulate a similar pattern on your installation.
Step 29: Rear driveshaft can now be loosened.
Mark the pinion flange-to-U-joint flange for reassembly. Drivelines are often balanced as a full assembly. In
any case, if there were no signs of imbalance, indexing will prevent an issue.
Note: Flange design and pinion seal I.D. can vary between
applications. This is the Dodge Ram approach and parts orientation. Make sure the new replacement seal and
parts are for your axle type and vehicle model application.
Step 30: Four bolts removed, the driveshaft is
carefully set to the side or wire-tied out of the way. On a one-piece shaft like the 140.5" wheelbase Ram
3500, keep the slip yoke in place at the transmission or transfer case. This will prevent oil from leaking
out and save time during reassembly. Protect the transfer case or transmission output
Step 31: Use of a yoke-holding tool and air
impact wrench is the safest way to remove the pinion nut. Used properly, an air wrench is far less risky than
a long breaker bar, socket and muscling the nut by hand.
Note: The other end of the yoke holder rests firmly against the floor in this project.
Know which direction the yoke tool rotates before applying force to the pinion
Step 32: Yoke holds pinion flange securely, and
nut comes loose readily with high force impact. You should use an impact-rated socket for this task. The
12-point socket size is 36mm on AAM 11.5" Chrysler applications. A quality impact socket can get expensive in
this size 12-point. Safety is at stake.
Step 33: Sometimes, especially on lighter axle
applications, the pinion shaft can be "danced" carefully through the flange and front bearing with an air
Caution: Use a tapered, blunt or round-end tool, not a chisel point! Impact force will
cause less trauma than "tapping" on the pinion shaft's end after the splines have been coated with factory
Step 34: The flange was so stuck with Teflon
paste that a puller was necessary to remove the flange. Advance Adapters has a great tool for this task on
axles with saddle-type yokes or smaller flange patterns than the 11.5" AAM flange on the Ram. Splines are not
tapered, the resistance here is from the paste—which took considerable force to
Step 35: This paste is more like cement after
110K miles of driving! Cleaning takes solvent and time with a brush. Inspect for nicks or a seal lip groove.
Polish the seal riding surface.
Step 36: Paste is evident on the splines of the
pinion shaft. This is all with good intentions, to prevent gear oil from wicking out the shaft splines in
service. Years past, Permatex 300D Gasket Sealer worked just fine for this task. Loctite Superflex RTV,
provided by Superior Axle & Gear, was our
reassembly choice...OEM calls for Teflon paste (like Loctite 592 PST). Your choice.
Step 37: At this point, the pinion gear remains
in place because the front/flange end bearing is a press fit onto the pinion shaft. The pinion shaft gets
"tapped" through the front bearing, which will be replaced with a new bearing cone and
Step 38: Not intended for reuse, this shaft was
"tapped" through the front bearing with considerable persuasion. During assembly, the front bearing is a
press fit onto the flange-end of the pinion shaft.
Step 39: An attempt with a curved pry tool
failed, and this works as well. Make sure your chisel point is sharp, tapered long and narrow. Catch the
seal edge without gouging the axle housing casting. Work the seal inward and out, avoiding force against
the iron casting. The seal came out in a minute, less time than rumaging for the specialty seal puller in the
Step 40: Seal out, the loose bearing cone
comes right out. You should now replace the bearing cups (shown) and cones. Note that there are
no marks on the housing from the seal removal with the chisel.
Step 41: Despite available specialty pullers, a
quick and effective way to remove bearing cups is via a hefty tapered punch with squared end. There are
reliefs at 180-degree points in the housing. The flat punch end can safely catch the shoulder of the
Caution: Tap back and forth between the two relief points,
carefully and uniformly, to prevent binding the bearing cup or damaging the housing bore! Wear eye
protection, the punch and bearing steel is very hard.
Step 42: Inner, gear head bearing cup is now
removed. Bore is unmarked, not blemished in any way. Use care and the two relief points for the blunt-end
Step 43: Again, the tapered punch works well on
the bearing cup at the pinion flange or nose end of the housing. This is a smaller cup. Stay on the
bearing cup edge and avoid damaging the axle casting. Tap side to side, 180-degrees
Step 44: A quality bearing spreader will lift
the carrier bearings from their seats without damaging the crown or flanges of the differential carrier. Do
not squeeze the spreader to the point of interfering with the differential flange.
Step 45: Using an adapter within the border of the carrier flange, this three jaw puller gradually works the bearing
loose. A puller of this kind has no means for holding the jaws inward. The better tool of choice here would
be a Posi Lock™ puller!
Step 46: Though tedious and requiring
considerable caution, this puller does remove the bearing. See how much more effectively the Posi Lock™
puller does this task (below).
Step 47: This is the Posi Lock™ gear and
bearing remover. The Model 208 shown will also accept optional transmission front bearing jaws for pulling
via the bearing's snap-ring groove! Force for this tool is 12-tons, with the side clamp preventing jaws from
spreading under this force.
Step 48: With an adapter on the carrier flange end, the Posi Lock grips the base of the bearing. If jaws are narrow
enough, they will fit the two notches in the carrier case. Here, the bearing spreader has lifted the bearing
cone high enough for the Posi Lock's jaws to safely grip the bottom of the bearing's inner race
Step 49: Original pinion shaft bearing is
removed to access the pinion depth shim. This is a crucial reference if you are not setting up the pinion
depth from scratch with discs, arbor, a pinion block, "scooter" and dial indicator.
Note: "Factory" method for setting pinion depth is now the full pinion depth gauge apparatus. This
is a definite for a new, blank axle housing. On a used or properly functioning axle, it is just as practical
to use the method described here, with dummy trial bearings and tooth contact tests—about as quick, too,
since we always run tooth contact tests, regardless of the pinion setting
Step 50: Angle steel towers with flat platforms
on top support the bearing spreader squarely. Towers offer a place for the large pinion gear to drop. Press
applies pressure to old pinion shaft's end, forcing the bearing off the shaft.
Step 51: The original pinion depth shim is
0.054" thick and numbered so. This is a baseline for setting depth. Adjustment of shim thickness will depend
up the tooth contact pattern results. We will start with an 0.054" shim stack built with new shims provided
in the Superior Axle &
Note: On these AAM axles, there are no +/- marks with thousandths of an inch "pinion variance"
indicated. That was once a reliable means for setting pinion depth on an axle—at least a starting point. See
the "dummy bearing" procedure described below and throughout the magazine. This makes pinion depth setup much
simpler and quicker if you do not have a pinion depth gauge fixture and specialty
Step 52: Superior Axle & Gear's installation
kit includes new shims for the pinion depth. (Original shim shown here.) A crush sleeve eliminates the need for
shimming the pinion bearings to set pinion preload. The crush sleeve is a big time
Step 53: LubeGard, a high lubricity, thin
assembly oil, works for us. Unlike the OEM recommendation of gear lube, this oil reduces friction
dramatically and is not temperature or pour sensitive at shop and reasonable outdoor temps. LubeGard also
helps prevent galling of bearings and machined surfaces during assembly. A light coating does the
Step 54: When pressing on new bearings, make
sure the bearing rollers and cage are not binding or getting squeezed in any way. Check rotation constantly.
Here, an adapter rides on the inner bearing collar as the bearing presses onto the flange. LubeGard prevents
galling and bind. Press squarely!
Step 55: This inexpensive, bottle-jack 20-ton
press frame gets a lift from a 20-ton air-over-hydraulic jack. The jack can work with compressed air or by
hand (hydraulically). Yes, there are expensive presses tailored for this work. This one works fine for less
frequent use. A dial pressure gauge would be a practical accessory.
Step 56: Step driver tool serves as a press
tool here. The aim is to avoid any pressure on the bearing cage. The tool must also clear the carrier flange.
Watch how this works...
Step 57: The tool rides inboard of the bearing
cage and outboard of the carrier flange. Pressure is against the inner collar (race) of the
Step 58: This tool also clears the differential
carrier flange at the inside diameter of the driver...
Step 59: The inside step of the tool allows the
bearing to end up below the lip of the carrier flange. (Tool must clear the lip.) Make sure that the bearing
seats completely. If necessary, improvise this tool with pipe. Protect both the bearing and
Step 60: Warming up the ring gear makes
installation easier. Using our parts washing cabinet heated at 145 to 150 degrees F, the gear goes for a
10-minute wash and winds up uniformly saturated with heat. Use protective leather gloves to set the gear in
place—quickly, while uniformly hot. Make sure the bolt holes align as you set the gear on the carrier flange.
Use pilot studs* if necessary.
*Pilot studs are simply long bolts of the same diameter and thread pitch as the ring gear bolt
holes. Cut the heads off, and if you want to be "creative", file a screwdriver slot at the end of each stud.
Two studs, placed 180-degrees apart, can act as a guide for the ring gear. Once the gear drops in place,
unthread the long studs from the ring gear threads.
Caution: Do not use a torch to heat the ring gear! The temperature described here is plenty;
this is alloy steel and not a candidate for much expansion. Too much heat also risks damaging the gear's case
hardening—and you don't want that to happen!
Step 61: Make sure ring gear bolts have thread
locker. (New bolts from Superior Axle & Gear have OEM type thread locker already on the threads.) Red
Loctite 271 is high strength needed for this application. Tighten bolts a few threads at a time in
cross, uniformly, and gradually come up squarely to torque setting. Do not cock or bind the
gear on the flange, make sure the gear remains square with the flange.
Step 62: Do not waste time with
Loctite 271 in place. Use as prescribed, and get ready to torque hardware to specification. 11.5" AAM axle
ring gear bolts take 175 ft. lbs. torque by OEM recommendation. Bring torque to specification in gradual
Note: Not only does Loctite 271 help prevent bolt loosening, it also helps maintain
original torque settings as the load on the ring gear tugs at hardware over
Step 63: This accurate 0-250 ft. lbs. torque
wrench makes several trips in cross, gradually increasing torque (75, 100, 150, 175, again at 175). Let bolts
set for five minutes after final torque is reached, then do the entire set at 175 ft. lbs. again. If you need
to brace the assembly, use safe anchor points and do not damage
Caution: There are errors in torque setting
recommendations in the Dodge Ram OEM shop manuals. Figures offered here were compared to G.M. and other
sources to determine the "correct" settings for the 11.5" AAM rear
Step 64: For setting pinion depth, a trial fit
can be quickly made with the use of dummy bearings. If the original bearings are in reasonably good
condition, carefully rout out the inside diameter of the bearing cones, just enough to finger-press fit the
bearing onto the pinion shaft. Used bearing and shaft measurements will be very close to the new pinion shaft
and new bearings.
Footnote: For axles without crush sleeves, make dummy bearing cups and cones for trial
fit. Remove a slight amount of material from the outer edge of old pinion bearing cups, just enough to finger
press the cups into the axle housing bores for trial shimming and testing. When the preload is correct, you
can install new cups in the housing and press bearing cones in place. Use the correct shim stack thicknesses,
as determined during the trial testing.
Step 65: Inexpensive drum sander arbor and
course sanding discs can remove the slight amount of bearing steel from the inner bore. Bearings are hard, so
use gritty abrasive to save time. Sand evenly to keep the bearing bore round. Continually trial fit the
bearing to the shaft. You want just enough sizing to permit the bearing to fit on and off the shaft squarely,
using hand force.
Step 66: These original bearings were both
fitted to the shaft by hand. There is no looseness to the fit, round and sized enough to slide onto the
shaft. Clean the bearings thoroughly and oil with light assembly lube.
Step 67: Now the dummy bearing fits to the new
pinion shaft/gear. A stack of shims is at the OEM thickness for the first depth check. The bearing slides
snugly onto the shaft and will come off with hand force. This serves as a quick trial fit
Step 68: A cup driver tool installs the new
inner bearing cup. This cup will be seated squarely and oiled lightly for trial fit. Again, LubeGard works
well to reduce friction and provides an accurate depth measurement and bearing
Step 69: Cup squarely in place and seated.
Bearing cups must bottom in clean bores and fit tightly, without galling or any interference from debris. For
accurate pinion depth and bearing preload settings, cups must fit properly. Confirm seating from other
Step 70: This is a professional grade, OEM type
bearing cup driver tool. It fits the bearing cup's taper and has a strong shoulder for squarely driving the
cup edge. The cup must be driven straight, not bind or gall, entering its bore
Step 71: Clean, prepped bore prior to installng
the front pinion bearing cup. This smaller bearing cup, if driven squarely, will enter the bore without
Step 72: Note that bearing cup seats squarely.
Look at the bearing seat edges from the opposite side. Be sure the cup seats all the way and snugly. This
assures proper preload settings.
Step 73: New bearing cups squarely seated,
pinion depth trial fit can start. The new pinion shaft will use the dummy bearings and a 0.054" shim stack in
this case. (Use your original pinion shim thickness for the first trial test.)
Step 74: New pinion shaft fits through the
dummy front bearing. The dummy bearings fit with the first trial stack of shims. Preload adjusters are oiled
lightly and threaded into the axle housing at each side. Adjusters must turn freely, without drag or
Step 75: For trial fit, the pinion seal is left
out, and so is the crush sleeve. Grind the crushed section off the old pinion nut, enabling it to thread on
and off the pinion shaft easily. This saves time and gives a quick read of pinion depth and the gear tooth
contact pattern. For now, tighten the nut to either the factory preload setting or zero play plus "light"
Step 76: Consider using a transmission
jack for the 11.5" AAM differential carrier. This assembly is heavy! Here,
a transmission adapter on a floor jack works well.
Step 77: The differential carrier goes into
position. Bearing cap bolts can be tightened with a box end wrench by hand at this stage, then backed off 1/4
turn or so to enable smooth rotation of the side adjuster nuts.
Step 78: A quick check of tooth contact pattern
can be done with a short stretch of painted teeth. This is the yellow marking compound furnished with the
Superior Axle & Gear installation kit.
Step 79: Set backlash close for this check, a
barely perceptible rock of the ring gear. Set a light load on the carrier bearings, using the spanner tool.
This will center the differential for an accurate read of pinion depth with bearing cap bolts
Note: Right away, it is clear that the pinion is not reaching into the ring gear teeth
deeply enough. Pinion gear rides high on the drive side of the ring gear
Step 80: Coast side also shows high-riding
contact. Note how the print is somewhat centered but high toward the "crown" or top ridges of the teeth. Mesh
can go deeper toward the "flank" or "root" of the teeth. This requires moving the pinion higher, more toward
the differential/axle shaft centerline.
Modern Tooth Contact Patterns and Gear Cut
Courtesy of American Axle & Manufacturing)
Tooth height is measured from the root (bottom of tooth) to the crown
(top of tooth).
The two-cut tooth is the same height at the toe (inside of
gear) as it is at the heel (outside of gear). The two- cut gear set has a natural "bias" condition; that is, the
pattern shows up slanted when the pattern is rolled with gear marking compound.
The five-cut tooth height is
shorter at the toe (inside of gear) and is taller at the heel (outside of gear). The five-cut gear set appears as a
square pattern when the set is rolled with gear marking compound.
Step 81: To roll the differential out without
risk of damaging the tone ring teeth, use a block of wood beneath the tone ring. The jack platform is able to
catch the weight and allow handling by one person if necessary. Do not bang these parts
Step 82: Much better! Even without full
pressure or drag on the ring gear, it is clear that the pattern is both centered properly and below the ridge
of the teeth faces (crowns). This is actually the second re-test. 0.057" was not enough, and the pinion head
has been raised to 0.059" in this case.
Step 83: Nice coast pattern, too! Spread across
the tooth, below the face/crown, and not too deep into the root or flank. This is with some resistance
created at the pinion flange to press and spread the yellow marking compound, making the impression more
representative of load.
Step 84: To remove the differential and install
a new bearing on the pinion shaft, the adjusters must be backed off. With cap bolts slightly loose, the
adjusters are moved with a round, narrow tool like this Torx driver.
Note: The Miller-SPX 8883A spanner will only loosen these adjusters so far. Adjuster
holes "disappear" into the housing, becoming narrow slits.
Step 85: Stack of 0.059" shims is fitted onto the
pinion shaft. New inner bearing gets pressed into place. Make sure the bearing is not bound, that the
pressure is against the bearing's inner collar only. Any pressure outboard of the collar can damage the
bearing cage, rollers or contact surfaces.
Note: 0.059" is correct for this installation. This is not a "universal" truth, and each
axle is different for both the OEM shim thickness and the correct shimming for the new pinion gear. The
difference in this case is 0.005", which also varies between installations. Look for your axle's correct
tooth contact pattern.
Step 86: Bearing gets pressed into position.
There is support from below on the inner bearing collar. Old race is strictly to keep the rollers and cage in
position. Force is against the inner bearing collar.
Step 87: Keep shims centered until the bearing
(inner collar) seats completely, with some pressure. You want compression of the shim stack. The new crush
sleeve is in position.
Note: This crush sleeve must be in place when you insert the pinion shaft through the
new front bearing and seal.
Step 88: Rear axle accepts the new front or
flange end bearing cone. Make certain that you install the crush sleeve on the pinion shaft before running
the shaft through this bearing. You can install the new seal first; this will help keep the bearing in
Step 89: Superior Axle & Gear provides
a tube of Loctite 'Superflex' blue RTV sealant in the installation kit. This is great stuff! A thin coating on
the seal jacket or edge backs up the neoprene seal. Use sealants sparingly. An even, uniform coating will
Note: Dodge Ram and GM applications use different yoke flange
types and seal I.D. sizes. Make sure you have the correct pinion seal for your application before installing
the pinion shaft and flange!
Step 90: With a tool chest draw full of seal
drivers, this approach works just as well. Tap evenly and prudently around the seal flange edge. Do not bend
the seal flange edge. Make sure the seal goes into the bore squarely.
Step 91: Seal installed properly, square and
evenly seated on the flat nose of the casting. Grease is inside seal lip. Spread grease evenly to lube the
pinion sealing joint. Make sure the pinion flange's sealing surface is clean. Polish with fine crocus cloth
or 3M Scotch Brite pad if necessary. Remove debris.
Step 92: Careful application of sealant can
reduce risk of any oil seepage. The Loctite Superflex works well, applied to the splines and the inside face
of the flange. When the flange is installed, this mating face will seal against the bearing inner collar. Oil
wicking is prevented by using correct sealants.
Note: OEM manuals recommend Teflon paste on these splines. You can do that if desired.
This install opted for Loctite Superflex Blue
RTV. Loctite 592 PST Thread Sealant would match OEM
Step 93: Wipe off excess sealant before
installing the flange on a clean, dry pinion shaft. Make sure the new crush sleeve is in place. Keep the
pinion shaft on-center. Run the pinion shaft's threaded end through the bearing while centering the flange
with the pinion seal. Keeping on center, bring these parts toward each other. Do not distort the seal lip or
Note: The pinion seal can be installed after seating the front bearing on the pinion
shaft. If that seems easier, install the flange without sealant, pulling the front bearing onto the pinion
shaft. Stop short of preloading the bearings at this point! Remove the flange and install the seal. Reinstall
the flange as shown here.
Step 94: Flange can be pulled into place with
the washer and modified (no locking edge) pinion nut used for your shim tests. Keep the shaft on center as
you tighten the nut. Use the flange holding fixture and air impact gun. Draw up slowly and steadily. Do not
crush the sleeve yet.
Step 95: Remove temporary nut after seating the
flange against the crush sleeve. The bearing is in place, securing the shaft as the nut and washer come off.
Coat the washer face with sealant, fill the cavity around the base of threads as
Step 96: Some use 271 Loctite high strength
(red) on the new pinion nut threads. The nut is self-locking, and Loctite 242 (blue), applied generously, is
a good safety margin and added sealer. Your choice.
Step 97: New pinion nut, provided in the
Superior Axle & Gear install
kit, now has coating of Loctite 242 on threads. If you use an air wrench at this point, be certain not to
over-tighten the crush sleeve! Torque required to crush the sleeve is very high (300-plus ft. lbs.). Use any
high torque air impact wrench with caution.
Caution: You must not over-tighten the crush
sleeve, or you will have to replace the sleeve with another new one.
Overtightening cannot be followed by simply backing off the nut,
although unaware installers have done this. The result is an unloaded front pinion bearing and risk of
bearing damage...Worse yet, the pinion nut could loosen, and the shaft and gear set
fail. The force of the crush sleeve is a key element for bearing preload, keeping the pinion nut secure and
holding the front pinion bearing in
Step 98: New
acquisition for this project is the Chicago Pneumatic Model CP7748 composite air wrench, a great value in the
$200 range. (We paid $199 plus tax through NAPA, including a nylon carrying case.) In real terms, this impact
can controllably crush a new pinion sleeve.
Note: See specs below. This 1/2-inch
air wrench lives up to claims, delivering peak torque at a lower CFM than much more expensive
products. Some manufacturers claim even higher torque output but require 29 CFM or an
unrealistically high rpm to do so. Watch the rpm and air requirements on air tool
The CP7748 is an
exceptional 1/2-inch air wrench for the price. Here are specs for the CP7748 air
Working Torque Range (fwd) 75-580 ft. lbs.
Maximum Torque (reverse) 920 ft. lbs.
Free speed 8200 rpm
NetWeight 2 kg/4.4 lb.
Average air consumption 5.2 CFM
Actual air consumption 21 CFM
Air inlet thread size 1/4-inch pipe thread
Minimum hose size 3/8"
Noise level 93 db(A)
Sound Power 104 db(A)
Step 99: Actual specifications for a pinion
bearing load are in inch-pounds. This flexbar Duro wrench has adjusted transmission bands and pinion bearing
preloads for decades. Reliable and easy to read as the shaft rotates, a flexbar torque wrench works well for
this kind of task.
Step 100: Crush sleeve coaxed very slowly with
the air wrench, the rotating torque was stopped at 22 inch-pounds for the new bearings. After stopping at 22
in-lbs, we lightly rap the shaft from both the front (shown) and gear head end with a sand head
plastic hammer. This seats bearings. Re-check rotating torque.
Step 101: Pinion flange is sealed and seated,
with the crush sleeve compressed at 22 inch-pounds of rotating torque (different than
start-up torque). 20-25 in-lbs is factory recommended for new pinion bearings in an AAM 11.5"
Step 102: Based upon the shim and tooth contact
tests, this should be the optimal height/depth for the pinion gear head. Marks on head of AAM gear are not
pinion variance readings like Dana and other axle types. The best setting overall is a correct tooth contact
pattern, correct backlash and 0.002" or less ring gear runout.
Note: Runout is the waver of the gear, not to be confused
with the required backlash between teeth. Ring gear runout is determined by either: 1) a magnetic stand and roller tip dial indicator
check while rotating the ring gear's smooth edge or 2) by checking backlash at 90-degree
increments of the ring gear and comparing results. The simple ring gear backlash test for runout works just
as well. Compare the variations at the 90-degree points as you check the ring
Step 103: Carrier and ring gear assembly rolled
into the axle for what should be the last time! Adjusters backed off, make sure the bearing caps line up with
the pin marks on the housing. Based on pre-tests and the right shim stack on the pinion, the gear set should
only require backlash and bearing preload adjustments—followed by a loaded tooth contact pattern
Step 104: All bolt threads have been cleaned
and wire brushed as needed. Here, Permatex 242 blue thread locker provides insurance against bolt loosening.
It also offsets natural loss of bolt torque over time.
Step 105: Bearing adjuster rings can rotate if
bearing cap bolts are slightly loose. Run bolts up hand tight then backed off 1/4 to 1/2 turn, leaving just
enough clearance for carrier bearing cups to move laterally as the adjusters
Step 106: Rotate the left/crown side adjuster
toward the carrier. Tighten just enough to remove gear backlash. Now you can tighten the right side adjuster.
At zero backlash with the left adjustment, remove the play from the right side
Step 107: Before tightening the bearing
preload at the right side adjuster, set up your dial indicator as shown. Angle should allow the dial
indicator plunger to move freely while meeting the ring gear tooth close to its rotational centerline.
Allow plenty of plunger range on the dial indicator. Finger snug the bearing cap bolts, allowing just enough
slack for adjuster movement.
Step 108: A quick setting for preload is 6
adjuster notches for new bearings. After carefully adjusting preload, check the gear backlash. Some like
0.008"-0.010" on an 11.5" axle. The Dodge Ram shop manual calls for optimal 0.005"-0.007" backlash
with an acceptable range of 0.003"-0.010". 0.006" is our goal with a 6-notch preload on carrier
Note: With backlash correct and preload at 6 adjuster notches, check the pinion
rotational load as shown. 42 in-lbs works very nicely here, a combination of the 22 in-lbs with pinion
bearings alone and the added carrier bearing preload (without axle shafts in
Step 109: If backlash is off with the preload
correct, you can move adjusters as needed and evenly—one notch loose at one side means one notch tighter at
the other side. Work this until backlash is right, and verify overall preload (42 in-lbs in this case).
Factory range with new bearings is 30-50 in-lbs for overall bearing load (pinion plus the
Note: 22 in-lbs at the pinion plus 20 in-lbs additional from the carrier achieves
the 42 in-lbs total. This is a good profile.
Step 110: Place some load on the pinion flange
and get a tooth contact impression. If okay, as shown here on both the drive and coast sides of the teeth,
install the axle shafts before the final, loaded test. Using Permatex 242 on threads, torque the bearing cap
bolts and install spring locks. Tighten cap bolts in steps and cross pattern. Torque to 153 ft. lbs. Index
springs at the adjuster notches; set lock spring bolts at 18 ft. lbs.
Note: Bearing cap bolts should be final torqued to 153 ft. lbs. ("207 ft. lbs."
is incorrectly stated in Dodge Ram manuals; that should read 207 N-m, which converts to 153 ft. lbs.) Once
tooth pattern is right, torque these bolts in cross and steps. After reaching 153 ft. lbs., let bolts stand
for a few minutes, then re-check. Verify pinion rotating torque, it should be correct at this stage—adjust if
Step 111: Run gear contact all the way around
before installing axle shafts. Note the correct depth into the teeth and the length of the contact area.
Backlash is now 0.0055", half way between 0.005" and 0.006", optimal for break-in to a final spec of 0.006".
There is no ring gear runout issue, a tribute to the quality of the gear
Note: There are two types of gear cuts. Our 11.5" AAM axle pattern follows the two-cut style.
For details on the modern ring-and-pinion tooth cutting styles, see the
American Axle & Manufacturing explanation and
Step 112: Install the axle shafts before final
tooth contact test. The best axle flange gaskets are Felpro's impregnated type that do not require RTV
sealant. (This impregnated #55328 gasket for the Dodge Ram came from NAPA.) Avoid
using RTV sealant, which has created issues like breakdown of silicone and migration of RTV into
bearings and gears. Use Permatex/Loctite 242 Blue on clean axle flange bolts. Make sure axle shafts are
Step 113: When installing axle shafts, hold the
flange in a way that keeps the axle shaft on center. This will prevent banging of parts and potential
damage to the differential case, bearings or splines. Oil shaft inner splines and slide the shafts without
force. Allow them to find their way into the side gear splines. Axle shaft bolt torque for the Dodge
Ram is 95-100 ft. lbs. Bring torque up gradually and in cross (below) with parking brake
Step 114: For this final torque test, the
adjuster locks are in place, torqued to 18 to 20 ft-lbs with Loctite 242 on the threads. Axle shaft flange
bolts should be tight so that the parking brake can be set to drag lightly. Create around 10 ft.
lbs. of pinion flange resistance for this tooth contact pattern test. Rotate pinion flange in both
directions...This is the correct final tooth contact pattern.
Step 115: Under load of 10 ft. lbs. drag from
the E-brake (no more), the tooth pattern looks good all the way around. Note the smoothing and clear
impression created as the brake drag simulates load. Coast, drive, relationship of heel and toe, root and
crown of teeth, this is a desirable result!
Step 116: Close-up of drive pattern shows ample
tooth contact length, the right engagement depth of pinion, with correct margins above and below the contact
areas. This is proof that 0.006" backlash will work well in this
Step 117: Correct coast pattern will run
quieter and provides long service life. On deceleration with a trailer in tow, down an 8% grade, it's
reassuring to know that the ring-and-pinion teeth engage like this!
Step 118: Wipe off the ring gear teeth;
denatured alcohol works well if needed. Vacuum out the axle cavity and around the differential to remove any
debris from the adjusters or marking compound residue.
Step 119: All hardware is torqued to
specification, tooth contact is right, and bearings have correct preload. This axle is ready for the cover
and an oil fill!
Step 120: Differential cover removed, it's time
for cleaning and paint. This OEM cover has minor rust formation, enough to require glass beading. Bolts can
be wired brushed.
Step 121: Rust beneath the OEM paint requires
glass beading. This is strictly surface, as the Ram 3500 has resided in a high desert climate since new.
Axles receive little paint in the manufacturing process. We'll fix this.
Step 122: Differential cover looks like new
after glass beading, wash and dry. A coat of primer and a fresh coat of semi-gloss black paint will restore
the cover. The inside will not be painted.
Step 123: Chrysler's differential cover gasket
is exceptional. This part can be reused if in good, leakproof condition. Use Loctite/Permatex 242 blue on
cover bolt threads. Install bolts using cross pattern.
Step 124: Tighten differential cover bolts in
steps to a torque setting of 30 ft. lbs. Do not over-torque, or you will distort the cover. Fill plug torque
is 24 ft. lbs.
Step 125: New OEM bolts at pinion flange are
recommended in factory shop manual. Align your disassembly indexing marks. Tighten bolts in cross, on the
Dodge Ram, the spec is 85 ft. lbs. Use Loctite 242 on clean bolt threads.
Step 126: Oil type is a controversy. My choice
here is Mopar Synthetic 75W-140 weight gear lube. Some believe break-in lube should be a 75W-90 or even a
straight 90 wt. The main objective during break-in is to protect the axle from
overheating. 75W-140 offers the widest range of temperature and load
Step 127: Four quarts of Mopar oil is 128 fluid
ounces. Fill for the 11.5" Dodge Ram axle is 122 fl. oz. Four quarts is close enough on a complete axle drain
with axle shaft removal and cleaned parts.
Step 128: After
putting fluid into the axle, we idled the truck unloaded (in low gear) for ten minutes on jack
stands to circulate oil and allow the bearings to fully saturate with oil.
We then installed wheels and tires before taking a light test drive on the road. With proper
break-in, this rugged axle will be trouble free for several hundred thousand
Axles require break-in after rebuilding, just like an engine! Axle concerns
during break-in are heat and load, as gear teeth establish a lifetime contact
Most builders recommend initial short trips under light load, allowing the axle
to cool down completely between runs of 10-30 miles. This goes on for a couple hundred miles, without
trailering or extreme acceleration loads. At 500 miles, towing can begin, with complete cool down periods and
short runs during the first tows.
Change the oil warm at 500 miles. This will remove any gear coating that could be
floating around the axle. Use appropriate oil at the refill, consider your climate, driving conditions and
axle temperature exposure.
For coverage of the Dodge Ram 3500's 9.25"
AAM front axle gear change, see the magazine's HD video rebuild of the AAM 9.25" beam front axle! Click here for access to the 4WD Mechanix
HD Video Network how-to video. Basic axle work is similar for G.M. truck applications that use the
9.25" center section.