Motive Gears "Checking Distance"

[jcws6]

I'm about to install a new set of Motive Performance gears in my Trans Am, and I decided to take a look at the install document that came with the gears. Here's the part I got stuck on:

"10. Each ring and pinion is pre-run and marked on the pinion face with its proper depth setting called the "Checking Distance". This dimension is from the face of the pinion to the axle center-line. A setting tool must be used to measure the checking distance. Pinion depth is adjusted by adding or subtracting shim distance. Stay +/- .002 of the pinion dimension."

The number marked on my 4.10s is 3.779. Is the "checking distance" something I should be worrying about? I know it's OK to reuse the stock pinion shim with factory gears, but what about with aftermarket ones like these?

[jcws6]

In retrospect, I realize that this is a pretty dumb question. But I stumped all you people, so there you go.

Checking distance is actually pretty much the same as pinion depth. It can be measured by the gear paint contact pattern test, or a special tool. I found two special tools that should do the job, if you're intimidated by that number on the head of the pinion (like I am).

There's the Ratech 10003 (around $29) & the Proform 66516 (around $107). The main difference is the Proform tool works on pretty much any rear end. The Ratech sells each tool specifically for a certain rear, and it requires a caliper to use. Both can be found at Summit. I bought the Ratech tool, and I'll report back if i actually end up using it.

[jcws6]

As it turns out, on the new Motive Performance gears, the checking distance is actually marked incorrectly. Basically, if you get a number that seems impossible (mine was 3.779), that's the distance from the back of the case to the centerline. Typically checking distance is from the pinion head to the centerline, but the Motive guy I talked to said the supplier they've been using F'ed it up. Just measure the pinion head thickness, subtract from the number on the head, and you'll get the REAL checking distance.