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I recently acquired a reproduction of a Porsche tool that is used to determine shim thicknesses use to set pinion depth in early Porsche transmissions. To use the tool, there are two dimensions that need to be known in advance. One is on the tool itself and the other is on a calibration attachment.

I am able to measure the calibration attachment, but due to the odd location of the dimension on the tool itself, I can’t measure it directly using what I have (micrometer, digital caliper, etc.) I have tried to take some related dimensions that I am able to measure to generate a value for the dimension I need (i.e. X/2 + Y = Z). However by trying to use various related dimensions, I am only able to generate accuracy of about .1 +/- mm. I really need it to be .01 mm or better.

I am hoping someone here has access to better measurement tools than I have and can help me out. In a perfect world, someone would have access to something like a coordinate measuring machine that uses some type of touch probe.

To give more details about this measurement the tool fits in place of the differential. So it rotates. The critical measurement is from the center of rotation (which unfortunately exists in empty space) to a flat plane machined on the exterior of the tool.

Can anyone help me out?

Thanks,

Richard

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

Bump!

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

That is way over my head!

However, how much of the transmission are you rebuilding? My experience with rebuilding Chevy differentials is that the factory pinion shim works with new pinions which can be machined to exact tolerances. It is the case that has varying tolerances.

So almost all the time, the factory pinion shim works with a new pinion and ring gear. I wonder if that might be the same for you? The carrier bearing shims are never right, so you have to measure backlash and adjust those shims accordingly.

I hope this helps or somebody with knowledge replies to you.

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Rubbin' is Racin'

Well the complication is that what I am rebuilding is not really a transmission, but a transaxle. So it has both the gear stack plus the differential in the same housing. So the output shaft has the pinion gear on the end. And the pinion depth ends up being a factor of everything on that shaft. So in effect every bearing race, gear, thrust washer, etc. is in effect part of the "spacer" that defines the pinion depth. And in addition to all of those items there are specific metal spacers (plus some paper gaskets) that are used to fine tune this.

Generally none of those go bad and need to be replaced. So if you are replacing worn syncro or dog teeth, you just use the existing shims and measure the old paper gasket so you know which new one to use. But if you need to do something like swap out gears you can affect the pinion depth which means checking it and maybe changing shims.

I know it is very common to just use ring and pinion gear paste to read the contact patterns to know when the pinion depth and backlash are set correctly. I will probably do that myself as well. I have some GM R&P contact pattern paste which is supposed to be the good stuff. But I also expect I will have some customers who want to do it by the book as the Porsche factory manual does not use gear paste, but rather this tool to set pinion depth. Either way the tool should get me very close if not right on and then I can verify via gear paste. Matched R&P sets from Porsche have measurements etched on them that are used with this tool to ensure proper depth. They apparently run them in together and adjust to get low noise and good wear characteristics.

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

One last thing to add is that if nobody has direct access to something that can help me out, can they point me to a local source?

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

Richard:
A CMM still needs 2 "touch" points to measure a distance. Depending on how big this thing is, and how accurate you need to measure, you might want to contact a shop that has an optical comparator (Shadowgraph), which would be accurate to, say, .001" over 6". A CMM would need to be fixtured to hold the guage, but would be more accurate. Maybe to .0002".

Maybe try J. A. King / NC Measurements http://ncmeas.com/ Bob Nadeau

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Brad

Brad,

Thanks for the link. I will give them a call.

Regarding the CMM requirement for 2 touch points... While the dimension is from the center of rotation on this tool (which is not a physical location that can be touched), the value can be calculated based upon some physical touch points.

Richard

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

Yes. At least 2. At least 3 for a circle.

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Brad

If you are willing to come down to Sanford some time, we have a Faro Arm that could probably take the measurements that you want as well as a comparator in our metrology lab. I'd have to ask a favor of our metrology lab, but I bet they wouldn't mind too much. I'd be pretty interested in learning more about how to use the Faro arm anyways, this might be a good opportunity. If you strike out with JA King (I think they are more a calibration company, not an actual measurement), let me know.

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2012 MX-5 Sport SUV