Found this over at another site, and thought I'd share. it's a really good how-to on gear installation.
Gettin the Gears Done
By Bill "BillaVista" Ansell
Photography: Bill Ansell
Technical Drawings: Lonny Handwork
Copyright 2005 - BillaVista Offroad Tech
(click any pic to enlarge)
Introduction
Setting up the axle’s ring and pinion gears – it’s one of those jobs that even the most experienced 4x4 builders approach with hesitation. There’s probably no other job performed on a 4x4 that carries more mystique than how to set up gears. Why does the job have the reputation it has? Does it deserve it? Can even the first-timer get decent results at home? The answers, in order, are: “You’ll understand by the end of this article”, “sort of”, and “Yep, you sure can.”
There are four main reasons the job is on that very short list of tasks most of us like to avoid:
Quick Ref Steps:
- Assemble all tools and parts in clean work space
- Disassemble, clean, and inspect all parts
- Make set-up bearings if required
- Measure and label new shims
- Calculate starting shim stacks
- Install ring-gear, starting shims, and set-up bearings
- Set backlash
- Set pinion depth and pinion-bearing preload
- Check contact pattern and adjust as required
- Re-check backlash and contact pattern
- Set carrier preload
- Install new races and bearings
- Final check of backlash, contact pattern, and preload
- Install pinion seal and new pinion nut
- Install cover and add lube
- Break in gears
- Change lube
Background
Automotive ring and pinion-gears are hypoid gears. Hypoid gears are gears that are shaped like a cone, have spiral teeth, and have offset axes (i.e. a line through the centre of the pinion will not intersect with a line through the centre of the ring-gear). Examine a ring and pinion and it’s easy to see that they have spiral (curved) teeth, but if you look closely you will also see that both the ring and pinion are shaped like the bottom chopped off a cone. The spiral teeth of the ring and pinion each have different spiral angles - creating a rolling or sliding contact as they mesh. This sliding contact begins gradually at one end of the teeth and continues smoothly to the other end. The contact is also overlapping; meaning contact on the next tooth begins before contact on the previous tooth has finished. This overlapping, sliding contact reduces noise and vibration and prevents the load from concentrating dangerously near either end of the tooth. In order to accomplish this sliding/overlapping contact without jamming, the curvature of the ring-gear teeth must be different from the curvature of the pinion-gear teeth. You can see in Figure 5 that the pinion-gear teeth curve much more than the ring-gear teeth. Because of this asymmetrical curvature, in order to achieve an equal amount of drive in both directions (imagine how odd it would be if you went farther forwards than backwards for an equal number of driveshaft revolutions) each of the teeth, on both ring and pinion, have unequal pressure angles. You can see an example of this by looking at the base (or root) of the ring-gear teeth in Figure 5 – notice how one angle is almost 90° and the other closer to 45°. The result is that the ring-gear teeth have a concave side and a slightly convex side. What all this fancy engineering means, is that in order to get the gears to be smooth, strong, and quiet we need to set them up very precisely. For example:
Note: There are many different types and styles of automotive axle gears. Some have removable centre sections (Toyota, Ford 9 inch); some use adjusting rings for setting carrier-bearing preload (14 bolt) and some use shims (Dana); some use a collapsible spacer to set pinion-bearing preload (Dana 35), some use solid shims (Dana 70) and still others use one or the other, depending on the specific model (Dana 60). As such, it is not possible for me to cover every single detailed procedure for every type of axle. The procedures and pictures for this article I developed while setting up the gears in a Dana 60 front axle. However, the theory, naming conventions, and basic order of steps, as well as detailed procedures such as reading the gear tooth contact pattern, are applicable to any axle.
Nomenclature
I’m a real stickler for accurate and consistent naming conventions – probably because I’m so easily confused! There’s another good reason though. I always want to know, not only how something works, but why; because often we find ourselves custom-designing assemblies and components. When you are putting together your own hybrid axle, for instance, it suddenly becomes really important to understand whether part #46 in the diagram is in fact an oil-slinger, a gasket, or a thrust washer – because the three things have very different roles. The parts-counter guy may not know or care what the difference is, all five of your manuals and parts books might call it something slightly (or completely) different - but it’s going to be really important to you because the if, where, and how you use one in your custom axle is going to depend entirely on your understanding of what the part actually is and what it does. Having said that – I understand that some commonly used terms are so well entrenched, even though they might not be technically 100% correct, that to use any other term would simply cause greater confusion. Sometimes there are also two or more correct terms for the same thing, so in order to keep things as clear as possible the following pictures and diagrams illustrate the terms used in this article.
Figure 1 – Ring-gear nomenclature
Key:
A – Top. The top of the gear tooth, a.k.a. Face, Top Land
B – Root. The bottom of the gear tooth, a.k.a. Flank
C – Heel. The outside-diameter-end of the gear tooth
D – Toe. The inside-diameter-end of the gear tooth
E – Drive. The convex side of the gear tooth*
F – Coast. The concave side of the gear tooth*
* Don’t be mislead by the terms “coast” and “drive”, as the ring-gear can be driven by the pinion on either side of the teeth. Which side of the teeth will depend on if the gear-set is standard or reverse spiral and whether the vehicle is going forward or in reverse.
Figure 2 – Pinion nomenclature
Key:
A – Head
B – Inner Bearing Seat
C – Shaft
D – Shoulder
E – Outer Bearing Seat
F – Splines
G – Threads
Figure 3 – Pinion assembly nomenclature
Key:
A – Pinion Nut
B – Pinion Nut Washer
C – Yoke (a.k.a. End Yoke or Flange)
D – Pinion Oil Seal.
E – Thrust washer
F – Outer Pinion-bearing
G – Outer Pinion Shims (a.k.a. Pinion Preload Shims)
H – Pinion-bearing Baffle
I – Inner Pinion Shims (a.k.a. Pinion Depth Shims)
J – Inner Pinion-bearing
K – Inner Pinion Slinger
L – Pinion (a.k.a. pinion-gear or drive pinion)
Figure 4 – Carrier nomenclature
Key:
A – Housing (a.k.a. Pig, Pumpkin, Chunk, Centre Section)*
B – Ring-gear (a.k.a. Crown Gear)
C – Carrier (a.k.a. Diff, Differential, Case)*
D – Carrier-bearing Cap
E – Carrier-bearing Shims (a.k.a. Diff Bearing Shims)
* Note that technically, Dana/Spicer refer to part C as the “Case – Differential” or just “Case” and part A as the “Carrier.” However, most of us have been calling C the “Carrier” (and hence D the carrier-bearings and so forth) for so long that I shall stick to that to avoid confusion.
When describing the various bearings used in the diff, I shall use the term “bearing” to mean the two-piece assembly, “cup” to mean the race by itself and “cone” to indicate just the roller-bearing portion.
Theory
OK, so we know setting up the gears requires care and precision, but the entire process is really just a matter of adjusting four separate but inter-related settings until they all fall within specification. The four settings are:
Figure 5 – Backlash
Backlash
Definition: The amount by which a tooth space exceeds the thickness of an engaging tooth.
Think of it as: Play between the mating teeth of gears or how tightly the ring and pinion gears mesh together.
How Measured: Measured as the free movement of the ring-gear with pinion held steady, in thousandths of an inch, using a dial indicator on the ring-gear. In other words, you’re measuring how much you can rotate the ring-gear before it engages the pinion teeth – this is the space between the teeth – called “backlash.”
Adjusted Via: Carrier shims. Adding shims on the ring-gear side of the carrier moves the ring-gear closer to the pinion, causing the teeth to mesh more closely, decreasing the amount the ring-gear can rock without turning the pinion, and therefore decreasing the backlash. Adding shims on the non ring-gear side moves the ring-gear away from the pinion, increasing backlash. Note that: carrier shims added to one side must be subtracted from the other, and vice versa, to maintain a consistent carrier pre-load.
Note: Backlash changes about 0.007” for every 0.010” the carrier is moved. The purpose of having backlash (i.e. the reason gears aren’t set-up tight, with no play) is to prevent the gears from jamming together. Lack of backlash may cause noise, overloading, overheating, or seizing and failure of the gears or bearings.
Figure 6 – Pinion Depth
Pinion Depth
Definition: Position of pinion-gear relative to the ring-gear centreline, expressed as either a mounting distance (measured from behind the pinion head to the centreline of the ring-gear) or a checking distance (measured from the face of the pinion head to the centreline of the ring-gear).
Think of it as: How close the head of the pinion is to the centreline of the ring-gear. Proper pinion depth makes sure the pinion teeth mesh with the middle of the teeth on the ring-gear – between the top and the root. Increasing pinion depth moves the pinion closer to the centreline of the ring-gear, moving the pinion “deeper” into ring-gear teeth and reducing the checking distance.
How Measured: The final determination of correct pinion depth can only be obtained by reading and interpreting the gear tooth contact pattern using gear-marking compound. There exist specialized tools for measuring pinion depth, but they are expensive, aren’t necessary, and are only used to calculate a starting point – final proof always lies in the contact pattern.
Adjusted Via: Inner pinion shims placed between the housing and the inner pinion-bearing cup. Adding shims moves pinion closer to ring-gear centreline, moving the pattern from the top to the root. Removing shims moves pinion further away from ring-gear centreline, moving the pattern from the root to the top.
Note: When adjusting pinion depth, begin with a starting shim stack and make large adjustments at first (10-20 thou) until the correct setting is bracketed; then make progressively smaller adjustments until the final setting is achieved. Adding or subtracting a single shim of one thou can, and does, make a difference. Increasing pinion depth also decreases backlash and moves drive pattern slightly towards toe, and coast pattern slightly towards the heel. Decreasing pinion depth also increases backlash and moves the drive pattern slightly towards the heel, and the coast pattern slightly towards the toe. Increasing pinion depth will also increase pinion-bearing preload unless the outer pinion shims are adjusted.
Pinion-bearing Preload
Definition: Bearing preload is a measure of the rolling resistance in a bearing or “bearing stiffness”. As a cone is pressed against its cup, the point or line of contact between the roller and cup becomes larger, friction increases and preload is said to be higher. Correct bearing preload is a trade-off between bearing stiffness and the wear resulting from the preloading.
Think of it as: How tightly the pinion-bearing cones are pressed into their cups and consequently how stiff they are to rotate.
How Measured: An inch-pound torque wrench is used on the pinion nut to measure the torque required to rotate the installed pinion.
Adjusted Via: Outer pinion shims placed between the face of the outer pinion-bearing cone and the shoulder on the pinion shaft. Adding shims causes the pinion-bearings to be spaced away from their cups, reducing pre-load and vice-versa. Add shims to reduce pre-load and remove shims to increase preload.
Note: Pinion preload is normally specified without the carrier or axle shafts installed, with the yoke installed and pinion nut torqued to spec but with no pinion oil seal installed. An installed carrier can add 2-4 in-lbs and a new oil seal adds approx. 3 in-lbs. Too little preload diminishes load-bearing capacity as the load-bearing surfaces between rollers and cup are decreased. Too much preload increases friction, resulting in excessive noise, heat, and rapid wear.
Carrier-bearing Preload
Definition: See pinion-bearing preload
Think of it as: How tightly the carrier-bearing cones are pressed into their cups and consequently how stiff they are to rotate. Also controls how tightly the carrier is held in the housing.
How Measured: Not possible to measure directly.
Adjusted Via: Adding or subtracting an equal amount of carrier-bearing shims to both sides of the carrier. Ideally, total carrier shim stack (sum of both sides) should be approx. 0.015” larger than the available space, and a case spreader should be used. However, a case spreader is not critical, and a good approximation of carrier-bearing preload can be made by ensuring the carrier can only be installed with a few good blows from a dead-blow hammer.
Note: If carrier preload is too little, carrier will move away from pinion under load (squirm or deflect), increasing backlash. This could lead to insufficient gear tooth contact, resulting in chipping/breaking of gear teeth.
Figure 7 – Dial indicating inch-pound torque wrench
Tools
You will require a good, complete set of regular hand tools including the usual hammers, punches, wrenches, sockets, and the like. Air tools are not a must, but will certainly make the job a lot faster and easier. You will also need the following:
Continued below...
Gettin the Gears Done
By Bill "BillaVista" Ansell
Photography: Bill Ansell
Technical Drawings: Lonny Handwork
Copyright 2005 - BillaVista Offroad Tech
(click any pic to enlarge)
Introduction
Setting up the axle’s ring and pinion gears – it’s one of those jobs that even the most experienced 4x4 builders approach with hesitation. There’s probably no other job performed on a 4x4 that carries more mystique than how to set up gears. Why does the job have the reputation it has? Does it deserve it? Can even the first-timer get decent results at home? The answers, in order, are: “You’ll understand by the end of this article”, “sort of”, and “Yep, you sure can.”
There are four main reasons the job is on that very short list of tasks most of us like to avoid:
- Tools. There are a number of specialized tools required to do the job, most of which are not commonly found in the home shop. The good news is, some of them we can work around not having and the others are cool tools you should have and have been meaning to get anyway!
- Time. There are several inter-related adjustments that must be made, each affecting the other, so that time and patience are required as one “juggles” the adjustments to arrive at the best solution. You can’t just set one thing in isolation and move on to the next – as you change backlash, so you change pinion depth; adjust pinion depth and you will alter bearing preload and so on. However, taking the time to do it right yourself is extremely rewarding.
- Precision. “Close” is definitely not good enough in gear set-up. There are exact specifications and minute tolerances that must be met – and with very good reason. The ring and pinion-gears are the place where all your engine’s power gets turned 90° - from the longitudinal axis of the crankshaft-driveshaft to the lateral axis of the axle shafts. Doing so places enormous stress on the differential carrier and gear teeth. In order to withstand these stresses without failure, the teeth on the ring and pinion must fit together, or mesh, precisely.
- Consequence of failure. Fail to set up the gears properly - and deflection under load could cause a spike in localized tooth pressure, chipping or fragmenting the gears. Also, bearings that are improperly set up can overheat and seize. The damage caused by poor set-up can be quite severe - often destroying other nearby parts.
Quick Ref Steps:
- Assemble all tools and parts in clean work space
- Disassemble, clean, and inspect all parts
- Make set-up bearings if required
- Measure and label new shims
- Calculate starting shim stacks
- Install ring-gear, starting shims, and set-up bearings
- Set backlash
- Set pinion depth and pinion-bearing preload
- Check contact pattern and adjust as required
- Re-check backlash and contact pattern
- Set carrier preload
- Install new races and bearings
- Final check of backlash, contact pattern, and preload
- Install pinion seal and new pinion nut
- Install cover and add lube
- Break in gears
- Change lube
Background
Automotive ring and pinion-gears are hypoid gears. Hypoid gears are gears that are shaped like a cone, have spiral teeth, and have offset axes (i.e. a line through the centre of the pinion will not intersect with a line through the centre of the ring-gear). Examine a ring and pinion and it’s easy to see that they have spiral (curved) teeth, but if you look closely you will also see that both the ring and pinion are shaped like the bottom chopped off a cone. The spiral teeth of the ring and pinion each have different spiral angles - creating a rolling or sliding contact as they mesh. This sliding contact begins gradually at one end of the teeth and continues smoothly to the other end. The contact is also overlapping; meaning contact on the next tooth begins before contact on the previous tooth has finished. This overlapping, sliding contact reduces noise and vibration and prevents the load from concentrating dangerously near either end of the tooth. In order to accomplish this sliding/overlapping contact without jamming, the curvature of the ring-gear teeth must be different from the curvature of the pinion-gear teeth. You can see in Figure 5 that the pinion-gear teeth curve much more than the ring-gear teeth. Because of this asymmetrical curvature, in order to achieve an equal amount of drive in both directions (imagine how odd it would be if you went farther forwards than backwards for an equal number of driveshaft revolutions) each of the teeth, on both ring and pinion, have unequal pressure angles. You can see an example of this by looking at the base (or root) of the ring-gear teeth in Figure 5 – notice how one angle is almost 90° and the other closer to 45°. The result is that the ring-gear teeth have a concave side and a slightly convex side. What all this fancy engineering means, is that in order to get the gears to be smooth, strong, and quiet we need to set them up very precisely. For example:
- Mountings must be rigid enough to minimize deflection of the gears under load, so that localized tooth pressure doesn’t rise too high and cause tooth breakage. This means axle housings must be true and square, bearing caps must be matched, and carriers must be strong.
- Gears must be held in proper alignment throughout a wide range of operating speeds and loads. This requires roller bearings in good condition and with proper pre-load.
- Tooth contact (mesh) must be carefully controlled so that tooth contact stress is spread out and not localized, otherwise surface damage to the teeth, tooth breakage, and noisy operation result. This means using only matched ring and pinion sets and accurately setting backlash and pinion depth.
- Proper lubricant must be used to withstand the high lubricant shearing forces encountered between the teeth as they mesh. This means using properly rated hypoid gear oil and setting enough backlash in the assembled gears to allow space for a sufficient lubricant film on the gear teeth. If the teeth mesh too closely (insufficient backlash) the oil may be squeezed out from between the teeth or become trapped at the root of the teeth causing heat and excessive tooth loading.
Note: There are many different types and styles of automotive axle gears. Some have removable centre sections (Toyota, Ford 9 inch); some use adjusting rings for setting carrier-bearing preload (14 bolt) and some use shims (Dana); some use a collapsible spacer to set pinion-bearing preload (Dana 35), some use solid shims (Dana 70) and still others use one or the other, depending on the specific model (Dana 60). As such, it is not possible for me to cover every single detailed procedure for every type of axle. The procedures and pictures for this article I developed while setting up the gears in a Dana 60 front axle. However, the theory, naming conventions, and basic order of steps, as well as detailed procedures such as reading the gear tooth contact pattern, are applicable to any axle.
Nomenclature
I’m a real stickler for accurate and consistent naming conventions – probably because I’m so easily confused! There’s another good reason though. I always want to know, not only how something works, but why; because often we find ourselves custom-designing assemblies and components. When you are putting together your own hybrid axle, for instance, it suddenly becomes really important to understand whether part #46 in the diagram is in fact an oil-slinger, a gasket, or a thrust washer – because the three things have very different roles. The parts-counter guy may not know or care what the difference is, all five of your manuals and parts books might call it something slightly (or completely) different - but it’s going to be really important to you because the if, where, and how you use one in your custom axle is going to depend entirely on your understanding of what the part actually is and what it does. Having said that – I understand that some commonly used terms are so well entrenched, even though they might not be technically 100% correct, that to use any other term would simply cause greater confusion. Sometimes there are also two or more correct terms for the same thing, so in order to keep things as clear as possible the following pictures and diagrams illustrate the terms used in this article.
Figure 1 – Ring-gear nomenclature
Key:
A – Top. The top of the gear tooth, a.k.a. Face, Top Land
B – Root. The bottom of the gear tooth, a.k.a. Flank
C – Heel. The outside-diameter-end of the gear tooth
D – Toe. The inside-diameter-end of the gear tooth
E – Drive. The convex side of the gear tooth*
F – Coast. The concave side of the gear tooth*
* Don’t be mislead by the terms “coast” and “drive”, as the ring-gear can be driven by the pinion on either side of the teeth. Which side of the teeth will depend on if the gear-set is standard or reverse spiral and whether the vehicle is going forward or in reverse.
Figure 2 – Pinion nomenclature
Key:
A – Head
B – Inner Bearing Seat
C – Shaft
D – Shoulder
E – Outer Bearing Seat
F – Splines
G – Threads
Figure 3 – Pinion assembly nomenclature
Key:
A – Pinion Nut
B – Pinion Nut Washer
C – Yoke (a.k.a. End Yoke or Flange)
D – Pinion Oil Seal.
E – Thrust washer
F – Outer Pinion-bearing
G – Outer Pinion Shims (a.k.a. Pinion Preload Shims)
H – Pinion-bearing Baffle
I – Inner Pinion Shims (a.k.a. Pinion Depth Shims)
J – Inner Pinion-bearing
K – Inner Pinion Slinger
L – Pinion (a.k.a. pinion-gear or drive pinion)
Figure 4 – Carrier nomenclature
Key:
A – Housing (a.k.a. Pig, Pumpkin, Chunk, Centre Section)*
B – Ring-gear (a.k.a. Crown Gear)
C – Carrier (a.k.a. Diff, Differential, Case)*
D – Carrier-bearing Cap
E – Carrier-bearing Shims (a.k.a. Diff Bearing Shims)
* Note that technically, Dana/Spicer refer to part C as the “Case – Differential” or just “Case” and part A as the “Carrier.” However, most of us have been calling C the “Carrier” (and hence D the carrier-bearings and so forth) for so long that I shall stick to that to avoid confusion.
When describing the various bearings used in the diff, I shall use the term “bearing” to mean the two-piece assembly, “cup” to mean the race by itself and “cone” to indicate just the roller-bearing portion.
Theory
OK, so we know setting up the gears requires care and precision, but the entire process is really just a matter of adjusting four separate but inter-related settings until they all fall within specification. The four settings are:
Figure 5 – Backlash
Backlash
Definition: The amount by which a tooth space exceeds the thickness of an engaging tooth.
Think of it as: Play between the mating teeth of gears or how tightly the ring and pinion gears mesh together.
How Measured: Measured as the free movement of the ring-gear with pinion held steady, in thousandths of an inch, using a dial indicator on the ring-gear. In other words, you’re measuring how much you can rotate the ring-gear before it engages the pinion teeth – this is the space between the teeth – called “backlash.”
Adjusted Via: Carrier shims. Adding shims on the ring-gear side of the carrier moves the ring-gear closer to the pinion, causing the teeth to mesh more closely, decreasing the amount the ring-gear can rock without turning the pinion, and therefore decreasing the backlash. Adding shims on the non ring-gear side moves the ring-gear away from the pinion, increasing backlash. Note that: carrier shims added to one side must be subtracted from the other, and vice versa, to maintain a consistent carrier pre-load.
Note: Backlash changes about 0.007” for every 0.010” the carrier is moved. The purpose of having backlash (i.e. the reason gears aren’t set-up tight, with no play) is to prevent the gears from jamming together. Lack of backlash may cause noise, overloading, overheating, or seizing and failure of the gears or bearings.
Figure 6 – Pinion Depth
Pinion Depth
Definition: Position of pinion-gear relative to the ring-gear centreline, expressed as either a mounting distance (measured from behind the pinion head to the centreline of the ring-gear) or a checking distance (measured from the face of the pinion head to the centreline of the ring-gear).
Think of it as: How close the head of the pinion is to the centreline of the ring-gear. Proper pinion depth makes sure the pinion teeth mesh with the middle of the teeth on the ring-gear – between the top and the root. Increasing pinion depth moves the pinion closer to the centreline of the ring-gear, moving the pinion “deeper” into ring-gear teeth and reducing the checking distance.
How Measured: The final determination of correct pinion depth can only be obtained by reading and interpreting the gear tooth contact pattern using gear-marking compound. There exist specialized tools for measuring pinion depth, but they are expensive, aren’t necessary, and are only used to calculate a starting point – final proof always lies in the contact pattern.
Adjusted Via: Inner pinion shims placed between the housing and the inner pinion-bearing cup. Adding shims moves pinion closer to ring-gear centreline, moving the pattern from the top to the root. Removing shims moves pinion further away from ring-gear centreline, moving the pattern from the root to the top.
Note: When adjusting pinion depth, begin with a starting shim stack and make large adjustments at first (10-20 thou) until the correct setting is bracketed; then make progressively smaller adjustments until the final setting is achieved. Adding or subtracting a single shim of one thou can, and does, make a difference. Increasing pinion depth also decreases backlash and moves drive pattern slightly towards toe, and coast pattern slightly towards the heel. Decreasing pinion depth also increases backlash and moves the drive pattern slightly towards the heel, and the coast pattern slightly towards the toe. Increasing pinion depth will also increase pinion-bearing preload unless the outer pinion shims are adjusted.
Pinion-bearing Preload
Definition: Bearing preload is a measure of the rolling resistance in a bearing or “bearing stiffness”. As a cone is pressed against its cup, the point or line of contact between the roller and cup becomes larger, friction increases and preload is said to be higher. Correct bearing preload is a trade-off between bearing stiffness and the wear resulting from the preloading.
Think of it as: How tightly the pinion-bearing cones are pressed into their cups and consequently how stiff they are to rotate.
How Measured: An inch-pound torque wrench is used on the pinion nut to measure the torque required to rotate the installed pinion.
Adjusted Via: Outer pinion shims placed between the face of the outer pinion-bearing cone and the shoulder on the pinion shaft. Adding shims causes the pinion-bearings to be spaced away from their cups, reducing pre-load and vice-versa. Add shims to reduce pre-load and remove shims to increase preload.
Note: Pinion preload is normally specified without the carrier or axle shafts installed, with the yoke installed and pinion nut torqued to spec but with no pinion oil seal installed. An installed carrier can add 2-4 in-lbs and a new oil seal adds approx. 3 in-lbs. Too little preload diminishes load-bearing capacity as the load-bearing surfaces between rollers and cup are decreased. Too much preload increases friction, resulting in excessive noise, heat, and rapid wear.
Carrier-bearing Preload
Definition: See pinion-bearing preload
Think of it as: How tightly the carrier-bearing cones are pressed into their cups and consequently how stiff they are to rotate. Also controls how tightly the carrier is held in the housing.
How Measured: Not possible to measure directly.
Adjusted Via: Adding or subtracting an equal amount of carrier-bearing shims to both sides of the carrier. Ideally, total carrier shim stack (sum of both sides) should be approx. 0.015” larger than the available space, and a case spreader should be used. However, a case spreader is not critical, and a good approximation of carrier-bearing preload can be made by ensuring the carrier can only be installed with a few good blows from a dead-blow hammer.
Note: If carrier preload is too little, carrier will move away from pinion under load (squirm or deflect), increasing backlash. This could lead to insufficient gear tooth contact, resulting in chipping/breaking of gear teeth.
Figure 7 – Dial indicating inch-pound torque wrench
Tools
You will require a good, complete set of regular hand tools including the usual hammers, punches, wrenches, sockets, and the like. Air tools are not a must, but will certainly make the job a lot faster and easier. You will also need the following:
- Foot-pound torque wrench - you need one capable of reading at least 250 ft-lbs for torquing the pinion nut, which affects pinion-bearing preload. You can try to do without, and use a “calibrated-by-feel” cheater bar or impact wrench but you will seriously compromise your set-up if you do.
- Inch-pound torque wrench – needed for reading pinion-bearing preload. “Experts” sometimes claim to be able to set this by feel. Those with a great deal of experience or a gifted touch probably can - but it's not a recommended approach for most. I certainly can’t and wouldn’t want to make do without this tool – again, it directly impacts one of the four major settings you’re trying to get right. Because you need to use the tool to measure torque while rotating the pinion, a “click-style” torque wrench will not work – you must use a beam-style or better yet a dial indicating torque wrench. Figure 7 shows the Armstrong quarter-inch drive, 0-75 in-lb model I talked myself into, despite its near $300 cost. I understand that beam-style wrenches can be purchased for much less at bicycle shops.
- Dial Indicator – needed to measure run-out, backlash, and carrier shim stacks. It might be possible to get backlash close simply by reading the contact pattern, but with specs in the range of four to ten thousandths of an inch, you’re going to get a pretty rough job without a dial indicator.
- 0-1” micrometer callipers – needed for measuring both old and new shims. You simply cannot do the job without this one.
- Set-up bearings – needed to avoid damaging real bearings and/or going insane while pulling and pressing the bearings on and off the dozen or more times you’re likely to need to while making adjustments to shim stacks. Take my advice – don’t even think about doing the job without set-up bearings. Besides, you can easily make your own set-up bearings from the old bearings – which also gives you all the reason you need to use new bearings when setting up gears – something I recommend anyway.
- Gear marking compound and brush – for reading the gear tooth contact pattern, the most critical part of the entire job – you simply can’t do without it.
- Bearing pullers and/or bearing separators with a press. Depending on their size, you will need one or both of these to remove the old bearing cones from the pinion and carrier. I have seen folks attempt the work with hammer and punch (ahem, cough) and the results are predictably disastrous. Don’t ask why I have a large pile of ruined bearings in the corner please!
- Bearing / seal drivers and/or press – appropriate drivers are required to install the carrier-bearing cones on the carrier (a press is much preferred, but it can be done carefully with hammer and driver), the pinion cups in the housing (a driver must be used), and the bearing cones on the pinion (press preferred for inner pinion-bearing cone, driver must be used for outer). You can often fabricate your own drivers, or at least the shafts, from scrap pipe or tube; but the face should be soft (aluminum or brass) to avoid damaging the new bearings.
- Pinion-nut socket – a 15/16” socket is required for the Dana 60 pinion nut, with a sufficiently thin wall to fit in the yoke.
- Pry bars – required for removing the carrier from the housing in most cases. A case spreader would be better still, but is not essential.
- Dead-blow hammer – needed for seating the carrier and/or pinion in the housing, especially if a case spreader is not used. A dead-blow hammer is like a combination of a mallet and a hammer: heavy like a hammer, soft-faced like a mallet to avoid damaging components. It also has a moving weight inside to reduce “bounce-back” when a blow is struck (hence the name “dead blow”).
- Punch or stamp – for marking carrier-bearing caps so that they can be reinstalled correctly.
- Assorted wrenches, sockets, screwdrivers, oil drain pan, silicone RTV, thread-locker, vice, hammers, parts cleaner, rags, and a 3-foot breaker bar or large impact wrench.
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