Technical Setting pinion depth without a pinion depth tool

Easy answer is pay a shop to do it or buy a tool.

I am completely rebuilding a 1967 GM Truck 12 bolt. What are cheap ways to measure pinion depth without buying a tool and still be precise? Precision ground metal that I have found are 18” long. I need a piece 6-8.5” long to go across the tops bearing surfaces. What have you used successfully to accomplish this? Or am I over thinking and should just get a piece of thick steel?

 

Easiest way I know is to use the shim that came out of it and check the tooth pattern. Adjust more or less as needed. If you are using stock gears, they are usually marked, so you can add or subtract from what came out to what is going in.

 

This is what I use, it's just a piece of flat bar bolted across the bearing split. Having checked, the split line has never been more than a few thou off the true centre line on any of the axles I've rebuilt. This is a Dana 44, but if IIRC the centre distance on the truck 12 bolt is the same @ 2.625" The car 12 bolt has a different centre distance. I always start off installing the original shim pack with the new bearings/pinion and take it from there.

 

Problem with that is not all carrier caps are machined so that the flat is on true centerline of the carrier bearings. Thats why kits include 2 bearing do-nuts and a shaft that is machined for accuracy towards true centerline.
TIP get another pinion bearing and hone so that the shaft is a real snug fit but can be removed easily, makes shimming a whole lot simpler without having to go back to the press each time--- final assy press on a new bearing

 

Never used one in 45 years working at dealers and on race cars.
Use yellow gear paint........

 

Thank you Rick...

 

I use a rig like Stueees , but I drill and tap the bar and screw a piece of all thread with a lock nut on it. I also round off the measuring end. I screw it real close to the pinion, about .025, and lock it down. Then I measure with feeler gauges. This gives me a reference as to the position of the pinion before repair. But I make the assumption that the new bearings will position the pinion a little higher. That’s why I allow some area for the feeler gauges. Just my way.






Bones

 

Now that’s a cool idea.

 

In my 38+ years, I worked for the primary manufacturer of gear production machinery and have built, helped build or seen built, thousands of axles. Pinion depth gage is used for production, but if you go by the tooth contact bearing & backlash, the gage isn't needed. With the time you take to (hopefully) make an accurate gage, you can set-up several axles without it.

 

i measure the old pinion gear and the shim, if there is one, and make the new pinion gear and shim the same thickness. then just shim the sides accordingly.

 

Thing is I’ve never used a depth tool either, but have only set a few reared a up. I think if you were doing daily like you were, great. But do one every 7-10 years or so and it can be a 3/4 day process. A tool, and knowing how to use it, would be a great help for a guy that doesn’t do it often

 

I have had good luck using depth end of a 6" dial calipers.

Mount a smooth straight plate across the flat rear cover surface, measure from plate to O.D. of the carrier bearing
(with out the cap) adding 1/2 the O.D. of that bearing will give you the axle center line measurement for your housing

Gets you close enough for the paint

 

That is how I have always done mine. Set the pinion with the original shims to start, and adjust according to the gear tooth contact pattern and backlash.
I haven't done a lot of rear ends, but I have had excellent results using this process. I learned the technique from of an old Landrover shop service manual.
Bob

 

Thanks for the info all! My goal is to take my time and do it right. I have spent days reading a researching. This is the last thing that really concerns me. I read an SA book on rebuilding GM rear diffs over and over. I have watched most of the gm 10/12 bolt rebuild videos on YouTube. The best one I found was done by Davin Rackow for Hagerty.

I do have an exact second head bearing to grind out and do my initial setup. I have a new 3:73 Richmond ring and pinion, Detroit Locker, a full set of Timken USA NOS bearings. I also have all the originals. I’ll take pictures and report back once it’s all done.
Thanks again!

 

Having setup hundreds of those type rear ends in my years as a GM line mechanic and as a fleet mechanic for the Govt.
I have been to the GM school for those types of rear ends. The pinion depth tool is nice , but the $ 800 price tag for the OTC tool is pricey unless you work at a Govt shop where the budget for equipment is ridiculous .
The tool makes setting up a 10 bolt or a 12 bolt or an 8.8 Ford a 15 minute job once you learn how the tool works. Just read the gauge and install the shims and then set the back lash.
Without the tool I have a set of honed bearings to use for setup . Once I get my desired pattern I remove my set up bearings and press on the new ones.
When I was dirt tracking most of the pure stock and hobby stock GM cars used a 10 bolt rear.
I was the go to guy to set them up and charged $ 150.00 if they brought me a clean rear end to set up
out of the car. It is so much easier doing it on jack stands or on the fixture I built for my engine stand than crawling under a car to set one up if you don't have a hoist to lift the car.

 

Amen to that, it is so much easier to do the setup on an engine stand. only takes a few minutes to make some simple adapters.

My basic setup for rear ends.


Using my home made carrier spreader on a truck 12 bolt in the stand.


Jaguar IRS bolted up ready for rebuild.

 

All of you guys recommending to use paint and read it, how do you keep from destroying the new bearing if you have to pull it off to readjust?

 

Bearing splitter on a press. Just don't support it so there is a bending load on the bolts.

 

I use a “set up” bearing. I take a pinion bearing and hone it out until it’s a slip fit over the pinion gear. After you get your pattern set, press on a new bearing for final assembly.

 

I just bought one of those for this...

What do you mean "just don't support it"?

 

Back in the day, I machined some aluminum donuts to go into the bearing saddles that a chunk of chrome rod (hydraulic ram shaft material] slid thru. Then with a spacer that sat on top of the pinion, the depth could be precisely measured.

 

This is a long lived thread...I always use the home made tool in this photo. The 'everyday' bearing puller in the top of the photo is almost always too thick to get behind the pinion and/or carrier bearings. I have a fair collection of the tubular spacers that go between the two 'halves' of my home made tool. The idea being that the halves of the puller can't tip inwards and mash the bearing cage. You can see the tool in use in the second photo. I've never damaged a bearing doing this over a lot of rear end rebuilds.

 

Taper roller bearings like all production parts have tolerances.
Refer to the attached PDF with some Timken tolerances.
I think the inner ring "stand" dimension might have the most a direct effect on pinion depth.
Timken says +.004"/-.000". Maybe their manufacturing is consistently tighter, but maybe not.
So production tolerances suggest the honed bearing's "stand" might be up to .004" different than the real bearing.

The tight fit on the shaft swells the inner ring and reduces the assembled end play and maybe even and the "stand" a little bit.

OEM tolerances for desired pinion depth are hard to come by.
A frequent reference is "0.002” to 0.004” is a small adjustment" .
So the .004" change in "stand" should show up as a visible change in the contact pattern.

Just sayin'

 

Make some set up bearings. Don't over think what you are doing. Start with original shim pack, play with the shim packs and see how the pattern reacts. Have fun and learn along the way. It's gears not rocket surgery.

 

Check out my build thread. I started working on the axle parts towards the bottom of page 5. I start with the setup bearing and go through the rebuild.
https://www.jalopyjournal.com/forum...pension-axle-and-brake-project.1131871/page-5

Paint is some oil based grease, I don’t think it actually is paint. It washes off with gear oil. It isn’t difficult, take your time and measure 5 times.

 

Just don't support it so there is a bending load on the bolts.

Excuse the 2x4's, that's the first thing I found to explain what I was trying to say. The top picture shows the correct way to support the bearing splitter on the press. (Also see Stueeee's post #22) If you place the supports like the bottom picture shows, the load is on the bolts and there is a high probability of bending them.

 

If you plan on rebuilding more than one differential then I could see going through the trouble of building a set up tool to make the process quicker . The old pinion may have a number in thousandths stamped on it. The new pinion should have a number also take the old shims from the old pinion, then add or subtract shims based on the difference between numbers on the pinions. As others have mentioned hone out an old pinion bearing so it slides on and off. With an old crush sleeve reassemble and check the pattern. if there is no number stamped on the old pinion start with those shims check the pattern and add or subtract shims till the pattern is correct.

 

Okay guys, here is the pinion...

Which numbers am I looking at?

 

In your case, with those numbers, it's probable that the 0.0 number refers to deviation from "stock."
So if we're setting this up, I'd go with the same thickness pinion shim, then see where the tooth pattern falls. Maybe you'll get lucky and hit the first time. In any case a bearing "knife" as shown above, along with press makes the job easier.
Just be glad it's not a Dana 60. The backlash is set by swapping shims under the carrier bearings. Big BIG fun!

 

Thanks guys. Gutted it and welded it up today.

The bearing came ot without a hitch. Had more problems with the axle bearings than the pinion.

All straight....ready to paint, and start reassembly.