915 pinion question

[triguy]

I have this new ring and pinion for a transmission but have a question about the calculation of the pinion depth. The new pinion has a marking of "N 1". So do I add 0.01mm or 0.1mm?

[triguy]

[jimmyjimmy]

sorry no idea ,but that word on the right isnīt so pretty in Dutch...

[triguy]

I believe that is the matting number to the ring or in this case letters.

[Dpmulvan]

That’s the optimum backlash number, other number is matching gear number.

[Dpmulvan]

Originally Posted by triguy

I have this new ring and pinion for a transmission but have a question about the calculation of the pinion depth. The new pinion has a marking of "N 1". So do I add 0.01mm or 0.1mm?

.1mm

[kevingross]

I've never seen a factory 915 pinion stamped / marked like this and take it this is an aftermarket set. Or was it supplied by Porsche? The "N" number is indeed the pinion depth correction in hundredths of a millimeter. So, absent information to the contrary, I would take this marking to specify 0.01 mm correction to be added to the measured value. But I would ask Hoer the question.

I know Hoer makes r&p sets for 356 series cars, was not aware they have/had anything for 901 and 915 transmissions.

[917_Langheck]

Klassic Automotive covered the N number question in this video: https://youtu.be/eUxyDlD86Ik?t=970

[triguy]

I have sent an inquire to HOER. I do believe it is 0.01mm after reading the page you supplied. Hopefully I will hear back and I will post it.

Yes I have seen that video. Lots of good information.

[gled49]

Porsche’s N #1 would be +.01mm

[triguy]

I got a bit sidetracked with summer but would like to get some miles on this car before it snows. I never did hear back from the gear manufacter so just going with N1 being 0.01mm. I made a tool to measure the pinion depth. I have a pinion depth of 66.195 with the original shims. So I believe the pinion is 0.115mm to deep. I have a question about gear pattern. With new SKF diff bearings preload is 28ft/lbs and backlash is 0.15mm. The new gear set is looking for 0.17mm. Here is some pictures of the pattern.





Any advise on what way to go would be great.

Thanks Neil

[Mark Salvetti]

Here area a few threads that may help.

http://forums.pelicanparts.com/porsche-911-technical-forum/274915-915-r-p-whine-how-do-you-get-rid-fix-2.html (Second page especially)
http://forums.pelicanparts.com/porsche-911-technical-forum/1034309-opinions-915-ring-pinion-contact-pattern.html?highlight=wear+pattern
http://forums.pelicanparts.com/porsche-911-technical-forum/1063543-checking-mesh-pattern-930-final-does-looks-ok.html?highlight=wear+pattern
http://forums.pelicanparts.com/porsche-911-technical-forum/1012138-comments-ring-pinion-mesh-pattern.html

Mark

[gled49]

You should be more concerned with the load mark, second picture. If the mark is out which it is, move the pinion out. More like this. Not sure you will get a fat mark like this.

[Matt Monson]

66.30 + 0.01 = 66.31mm. If you’ve got it at 66.195 mm, you are correct that it’s off by 0.115.

[triguy]

So I have been moving the pinion out 0.05mm at a time and the pattern is moving to the center of the tooth. So now I am at a pinion depth of 66.465mm, 0.155mm farther out than it calls for. Backlash is 0.20mm and 0.17mm is my spec for this gear set.




I do have a stack of shims under the bearing retainer plate now, 60mm (The case was machined during the bearing hole repair). I dont think I want to go much more even though the pattern is coming. Does anyone know what way the pattern moves under load?

I am not sure if I should adjust the backlash in at this pinion depth or go back closer to the disired pinion depth and not worry about the pattern.

[stownsen914]

Interesting that it's so far off from the spec?

[gled49]

Not that unusual. If I get a good pattern on the number I consider that a great outcome. In reality most good patterns are not on the number. I use both methods, I track the pattern movement with numbers and if I get a good pattern I’ll use it. Jon B and CMS use the numbers and I will also unless the pattern is horrible. The 935 manuals advises u to use gear contact pattern to rule out measuring or transcription errors. It’s your choice.

[Matt Monson]

The thing to keep in mind is that the set up numbers porsche provides have historically been based on quietest running. That doesn’t always coincide with the best pattern if one prints it.

[triguy]

I wanted to print the pattern to help verify my measurement. As it seems I won't get both a good pattern on the right measurement with this gearbox. I have read a lot of threads on this and it does come down to deciding what path to follow. I think both will give acceptable result. It is the lack of 915 experience that makes it hard to decide. Quiet gears are always nice. Just don't want to here them over the M&K muffler.

[kevingross]

Originally Posted by Matt Monson

The thing to keep in mind is that the set up numbers porsche provides have historically been based on quietest running. That doesn’t always coincide with the best pattern if one prints it.

Quite correct. I've said this before on this forum, so forgive me if I sound like a scratched record (if any of you know what that means...) The "bluing" aka. pattern marking does not work for two reasons.

• Porsche (well, Getrag) determines the ideal depth by loading the transmission. That is, there is torque applied to the input and (opposing) output shafts. This shifts the pattern on the teeth, and the contact patch you see while static testing on the bench is not where the patch is when driving the transmission.
• The specified tolerance is +/- 0.05 mm. You will never see that delta with your eyes and bluing.

I'll give you points for initiative in coming up with your own tooling. But there's no way you can take confidence that you've got it right.

Bear in mind that a hypoid gear design puts significantly greater stresses on the pinion teeth because the pinion-to-crown contact patch moves both up and down the tooth (like a non-offset spiral bevel gear set), and inward and outward, that is radially with respect to the differential's axis. Porsche's reference to "quietest running" should be taken to be synonymous with "least mechanical noise, stress, and heat energy." The 915 pinion gear is not generous with its tooth root width and length, which are the critical dimensions when considering its mechanical strength and ability to tolerate non-optimal set-up.