The preload is deterimed by the shims between the bearings. You can adjust the pinion depth by changing the shim between the bearing and the pinion head, and it will not affect preload.
Here read.
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.
