XPerts: Ring an pinion patterning

[ChrisBennet]

My friends and I have been playing with ring and pinions the last month or so. (This was all made possible by my friend Palmer who made an extremely neat tool for setting the pinion depth.)

I'm curious about the ring pattern we're seeing. Comments? (We're trying to learn here so don't be bashful.)

Here's a stock, a delivered from the factory 915 R&P:


Here's a new 930 R&P (a mystery one):


In case you're curious, here's the pinion depth tool Palmer made. He took his old diff and mounted a digital dial indicator inside it. He mounted something on the side for the dial indicator probe to stick through and faced it off to be exactly 66.0mm from the centerline. (Stick something flat on the side and zero the indicator.)


Powerhaus told my buddy they would set up his 930 R&P for $900 so even accounting for a broken part or two he's ahead of the game.
-Chris

[Chuck Moreland]

Chris, can you provide more details on the tool and how it's used?

[Grady Clay]

Chris,

What “paint “ are you using on the ring gear?

Thanks for taking this up. I’ll try and duplicate your experiments with some old transmissions. I have the Factory tools.

One issue with comparing patterns to properly positioned pinions and properly set backlash is the “running for minimum noise” that the Factory numbers represent. The question becomes; should we simply set to Factory numbers regardless of the pattern or should we get the best pattern regardless of the setting numbers?

I think it is potentially very useful to see the pattern of gears as set by the Factory and run for a long time. I would like to then replace bearings and reset to the original numbers. I suspect the pattern will change. The question is will the gears become noisy (whine)?

Best,
Grady

[ChrisBennet]

Originally posted by Noah
Chris,
Here's a pic of my ring gear, from when I put a 7:31 CWP in my gearbox. I was told that this contact pattern "looks good" by a few different people who know what they're talking about (or at least I think they do). I did this work a couple of years ago and have put several thousand miles (including a few track weekends) on the box, and there is no noise. FWIW, it looks to me like you might be checking the contact pattern in reverse, instead of a forward gear? Shouldn't the opposite face of the ring gear teeth be checked?

The way I set up the pinion depth was that first I spent about four hours fiddling around with the factory tool. I couldn't figure out how it works (I'm pretty sure it was missing parts), so I took John Walker's advice and transfered the shim stack from the 7:31 donor tranny to my tranny, bolted everything together, and checked the contact as seen in the pic below. IIRC, John said that 80 percent of the time all you need to do is keep the shim stack and CWP with eachother, and you'll be good to go, because the tranny case castings are so consistent.

Of course, this doesn't apply if you don't know the thickness of the original shim stack, or there's some other reason why you need to check the pinion depth...

BTW, $900 to set the pinion depth sounds like crazy talk to me. I talked to Hayden at Wevo, and IIRC he said he charges for about three hours of labor to do it.

Hi Noah,
I think your pattern is on the coasting side but like I said, we're learning. I found this from Dana/Spicer on setting up ring gears:
Ring Gear and Pnion Tooth Pattern Interpretation
None of the 3 ring a pinion we set up have been run yet so I can't report on how they sound.

-Chris
P.S. It was nice finally meeting you in persion the other day.

[ChrisBennet]

Originally posted by Grady Clay
Chris,

What “paint “ are you using on the ring gear?

Thanks for taking this up. I’ll try and duplicate your experiments with some old transmissions. I have the Factory tools.

One issue with comparing patterns to properly positioned pinions and properly set backlash is the “running for minimum noise” that the Factory numbers represent. The question becomes; should we simply set to Factory numbers regardless of the pattern or should we get the best pattern regardless of the setting numbers?

I think it is potentially very useful to see the pattern of gears as set by the Factory and run for a long time. I would like to then replace bearings and reset to the original numbers. I suspect the pattern will change. The question is will the gears become noisy (whine)?

Best,
Grady

Hi Grady,
We used Prussian Blue. It didn't work as well on the 915 because I didn't get all the oil off the gears first (I missed some).
-Chris

[ChrisBennet]

Originally posted by Chuck Moreland
Chris, can you provide more details on the tool and how it's used?

The purpose of the tool is measure the distance from the centerline of the differential to the face of the pinion. Palmer's tool positions the dial indicator inside a donor differential so it can do that.




To use the tool:
1. Put a bunch of differential shims on one side of the tool to space it up or down so the end of the dial indicator hits the face of the pinion off center. (The center of the pinion has a hole in it.)
You could use a thin shim if you wanted.
2. Put the bearings you are going to use onto the tool. (Palmer has reduced the diameter of the diff ends a little to facilitate this.)
3. Place something flat across the face where the dial indicator probe sticks out and zero the indicator. Now readings will be relative to 66mm.
4. Put the tool into the case and position the end of the dial indicator up against the face of the pinion gear and put the side cover on.
5. Look down through the side cover opening and read the dial indicator. Example: Indicator reads 0.54mm, pinion depth is 66.54mm.

Note: This is a digital dial indicator that lets us control the sign of the reading. If you made this tool using a normal dial indicator the reading would actually be negative 0.54.

For a 930 transmission the pinion depth is greater than the dial indicator probe can reach. To get around this you attach a "gage" of known thickness to the end of the pinoin. We discovered that a large ceramic magnet from Radio Shack were very flat and ideal for this purposes.

-Chris

[304065]

Chris,

There's a pretty good web site by a guy who does a lot of Toyota rock crusher diffs. . . not Porsche obviously but there are some excellent pattern images. http://www.gearinstalls.com/index.htm

The fixture is way cool.