Yes, those etched numbers on the top of the pinion acutually have meaning and are quite important to getting a good pattern.  If you don't have these numbers on your pinion gear, do not fear, you can still get to where you need to start checking your depth with these methods.

Let's say we were working on a Dana 60 gear setup.  The nominal checking distance for a Dana 60 pinion is 3.125”. However, each matching gear set will have its own ideal checking distance. Often, a pinion will be marked with a figure that shows, in thousandths of an inch, the difference between the nominal distance and that gear set’s ideal distance. The pinion in the image shown is engraved with “+4” which indicates that its ideal checking distance is four thousands of an inch greater than nominal, or 3.125” + 0.004” = 3.129”. The exact figure is not really important to us, but if both pinions have such a marking the markings should be recorded now as they can be used to help calculate the starting inner pinion shim stack. Copy down the number and its sign from both old and new pinions. If you’re starting without an old gear set or if one of the pinions doesn’t have a checking distance marking – don’t bother, as you will have to use a different method to calculate a starting shim stack.

If you are just changing the gears or if you are replacing the carrier and re-using the old gears, the quickest method is to simply start with new shims equal to the old shim stacks. You should measure each shim individually when calculating the old and assembling the new shim stacks, as measuring a stack of shims together can lead to inaccuracies. Note that any slingers or baffles form part of the inner pinion shim stack. This means that if you are re-using gears that had a slinger or baffle (or both), but you aren't re-using the slinger and/or baffle, you must add the thickness of the deleted slinger/baffle to the starting inner pinion shim stack. The same is true in reverse. If you are using a slinger and/or baffle with a set of gears that didn't use them originally, you must delete the thickness of the newly added slinger/baffle from the starting inner pinion shim stack.

If both the old and new pinions have checking distance markings (aka depth codes), the starting point for the new inner pinion shim stack can be further refined as follows:

• calculate the size of the old shim stack.
• calculate the adjustment by subtracting the new pinion marking from the old, being careful to observe the signs. For example, if the old pinion marking is (+4) and the new pinion marking is (-2) the result will be (4)-(-2) = (4)+(2)=(6). If the old number was (0) and the new number (+2), the result would be (0)-(2)=(-2).
• If the adjustment figure is negative, subtract that many thousandths of an inch from the shim stack and if the adjustment number is positive, add that that many thousandths of an inch to the shim stack.
• Example: old shim stack = 0.035” (35 thou), old pinion marking is (-2), new pinion marking is (+1). Adjustment =(-2)-(1)=(-3). New shim stack will be (35)-(3)=32 thou.

Alternatively, you can use the following chart to calculate a new inner pinion shim stack on our Tech Info page