915 Transmission gearing

[811SWB]

I'm in the process of re-gearing my 915 transmission and I would like to know if any of the gears can be swapped to reverse the ratio. Ex: Can a 4th gear RP 27:25 be swapped around and be used as a 25:27? If possible could it be used in a 3rd gear position?

The real question I have is, can a reversed 3rd gear be used as a 4th gear and can a reversed 4th gear be used in the 3rd gear position?

Can 5th gear be reversed??

811SWB

[cstreit]

Unfortunately you cannot swap gear sides. You couldn't get a syncro on the fixed gear (non idler) and the shafts are a different size.

[KTL]

Chris is correct. The loose and fixed gears cannot be exchanged. However you can "relocate" gears. For instance my close-ish ratio transmission has a OR ratio (1.125) for 4th gear. Which is actually a 3rd gear ratio for the early 915 4 spd and it has been moved to the 4th gear position.

Take a look at Guard's gear listings and you can see some overlap between the 3rd & 4th gear ratios.

http://www.guardtransmission.com/app_911.html

[Matt Monson]

You can run the stock 3rd gear in the 4th position, but it's not flipped. That was part of one of the homologation options for the SC-RS
3.18
2.00
1.60
1.26
1.00

It lets you reuse one stock gear and the mainshaft in a race box. 5th gear can be adjusted a little bit up or down to suit tire size, engine powerband, rev limit, and desired top speed.

Regards,

Matt