Can you set pinion depth by gear tooth contact pattern?

I am looking into my GM manual on this subject and they say that doing this confirms the correct shim was used.

So, if this is so, what is the use of the VERY expensive tools that check for pinion depth? Can't I just resuse my old shim and confirm in contact pattern? if pattern, wrong, adjust shim.

My scenario is a true bummer. When I took my cover off, I found my pinion had lost a tooth. So I went from just replacing bearings to now replacing my whole gear set. But now I am stuck in my garage without the proper way to check my pinion. Everything else I can do and have the tools for.

Oh well, I wanted to get 4.10's anyway.

Tooth pattern is an indicator of correct pinion depth. So, Yes you can set the depth by checking the tooth pattern.

The reason people use the correct tools to check depth is so you don't have spend time taking the thing apart in trial by error fashion. With the correct tools you may only have to remove the pinion to change shims once instead of several times.

Anyways, the following two rules apply:

1. Pinion depth sets your tooth pattern
2. Ring gear off-set sets your lash.

Red,

That is exactly what I needed to know.

Now Red (or anyone else) another question: as a rule of thumb:thumb: will .010 always be needed in order to see a difference in contact pattern?

Just trying to get an idea just in case my old shim does not give me the correct pattern.

Again thanks.

In my experience, reading the pattern is almost as much art as it is science. You'll almost never get a textbook pattern on both the drive & coast sides. I just spent 3 full evenings doing one of my 12 bolts. There was no pinion depth marked on the pinion so I had to start from scratch. I went from obvious too deep to obvious too shallow in about plus or minus .010" from the best compromise pattern. I was making .002" changes on pinion depth on every trial. If your doing this with the rear in the car and you don't have a spare pinion bearing clearanced for a shim trials, be prepared for a long and difficult process. Usually if you have the depth setting stamped on the pinion, and you set to that depth within .001 either way, the pattern will come out pretty darned good. I'd look to borrow a good depth checker. Beware of the cheesy depth checkers. The good ones have calibrated stylus' and sit squarely in two spools which sit in the carrier bearing saddles. Even with the good checkers It is tough getting repeatable depth readings. One little spec of dirt can drive you nuts. I don't mean to scare you off but getting a good setup is not usually as easy as swapping some shims and bang your there. As you know poorly setup R&P will howl & whine, and the tooth contact stresses go up rapidly since the contact patch is all wrong.

Hope I helped and other opinions are respected,

Steve

Start with the shim thickness that is on the old pinion.

Like ShoeBox said, start with the Pinion Shim that you already have. The whole point of the tool is to measure for variations in the housing. Variations in the pinion gear itself are identified by a stamping on the pinion. Since you are re-using the housing, the pinion shim, unless the pinion is marked to indicate otherwise, should be OK.
Not to mention the gauge is more of a "guide". Just last week I replaced a housing and gearset on an 8.5" rear, and the gauge indicated that I needed a .039" pinion shim, yet I had to work my way down to a .036" to get the pattern I needed. The pattern is what you need to follow. It is a true indicator of how the gears are positioned.

Thanks all, you have given me the confidence to move forward on a project I have never done before. Getting the gears in next week and I will tell you all how it went.


Ben