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neilca's Avatar
 
Join Date: Oct 1999
Location: Marietta, GA
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901 gear change

I am building a 901 gearbox with shorter gears for shorter tracks. So far I have confused myself on the use of the "N" gear. I want to use an "N" in the fourth gear slot. All the charts say it can be done, but does it become a "Z" gear when it is placed as a fourth gear? Seems it has to "flip" to fit.

Thanks,
neilca

Old 02-12-2009, 07:18 AM
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The factory never flipped- the thrust axis reverses because the gears aren't straight-cut, so when the gears are under load, there is an axial thrust on the shafts. You want the load going all the same way.

Everyone says "I flip gears and it works fine, never had any problems" but I wouldn't do it in my own box, race or street.
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Old 02-12-2009, 07:56 AM
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The factory did flip these gears. The "M", "S", and "O" gears were used in both 3rd and 4th, depnding on the year. Check it out here

http://www.roadglue.com/wiki/index.php?title=901_transmission
Old 02-12-2009, 09:22 AM
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Flipping 901 Gears
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'66 911 #304065 Irischgruen
‘96 993 Carrera 2 Polarsilber
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)
Old 02-12-2009, 10:45 AM
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Thanks John,

That series adequately explained the side thrust issue.

neilca
Old 02-12-2009, 11:41 AM
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kenikh's Avatar
 
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This comes down to personal preference on how comfy you are with the side load isse. I have a flipped gear in 3rd, FWIW.
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Old 02-12-2009, 11:50 AM
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My original question was if you take an N gear and place it in the fourth gear slot does it now become a Z?
Old 02-12-2009, 11:55 AM
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3 restos WIP = psycho
 
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yes.

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Old 02-12-2009, 11:59 AM
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