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Posted by: brant Sep 25 2017, 04:17 PM

Hello everyone,

I have an "M" gear ratio in my stock
I'm going to need to build a really short ratio box in the future
and have decided that there are 2 different set of ratio's I could go with to obtain what I'm looking for....

so how do I tell if the M ratio I have is a 3rd or 4th position M?

I'm guessing that it has to do with the direction of the gar angle, and which side the slider faces...

can someone spell it out for me so I can decide which path to take and what ratio's to start searching for...

I expect to start a separate WTB thread in the classifieds after I decide my path
thanks in advance

brant

Posted by: oldie914 Sep 26 2017, 12:56 AM

You have to consider a couple of things:
Porsche marked gears with the Roman numeral I if it was made to be installed on the mainshaft and II if it was to be installed on the pinion shaft.
For the third gear position in the transmission, the mainshaft gear (marked I) is fixed with internal splines while the pinion shaft gear (marked II) rotates on the needle bearing.
For the 4th gear position, things are reversed. The gear marked I rotates on the needle bearing and the gear marked II is fixed with splines.
Conclusion: If you have an M gear pair and the gear marked I has internal splines, it was made as a 3rd gear. If the gear marked I has a needle bearing race, it was made as a 4th gear.

Posted by: brant Sep 26 2017, 07:20 AM

QUOTE(oldie914 @ Sep 26 2017, 12:56 AM)

You have to consider a couple of things:
Porsche marked gears with the Roman numeral I if it was made to be installed on the mainshaft and II if it was to be installed on the pinion shaft.
For the third gear position in the transmission, the mainshaft gear (marked I) is fixed with internal splines while the pinion shaft gear (marked II) rotates on the needle bearing.
For the 4th gear position, things are reversed. The gear marked I rotates on the needle bearing and the gear marked II is fixed with splines.
Conclusion: If you have an M gear pair and the gear marked I has internal splines, it was made as a 3rd gear. If the gear marked I has a needle bearing race, it was made as a 4th gear.

Thank you!

Posted by: Montreal914 Sep 26 2017, 07:33 AM

You have probably seen these charts...

http://www.blueskymotorsports.com/index.php?option=com_content&view=article&id=17&Itemid=6

Posted by: brant Sep 26 2017, 09:59 AM

QUOTE(Montreal914 @ Sep 26 2017, 07:33 AM)

You have probably seen these charts...

http://www.blueskymotorsports.com/index.php?option=com_content&view=article&id=17&Itemid=6

yes
and thank you....

unfortunately my M ratio is 3rd, and I need it to be a 4th position gear
oh well....

needing to define my shopping list
find an I ratio, and possibly an H, or M ratio too
brant

Posted by: Dr Evil Oct 6 2017, 08:58 AM

Brant, is this for the box at my shop? We can talk, I have parts, and you can flip the M and it will not be an issue if you want to save some $$.

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