Honda MotoGP Hodaka MX – A Tale of Two Gearboxes

honda-hodaka-transmissionHonda’s new MotoGP transmission reminds us of another unusual design from the 70’s – the Hodaka.

Honda MotoGP vs Hodaka Trail Bike

After much early season rumour, it was revealed that the Honda MotoGP bikes are using a “quick shift” type transmission.

Rather than the more usual, ignition/fuel kill that activates when the rider moves the gear lever – which unloads the transmission and allows a shift – the Honda system requires no such time wasting engine kill.

Revealed via unearthing of patents lodged by Honda, the transmission (see diagram below)  changes gears in an entirely new fashion, a movable rod (1) operates a series of mechanical components (2) inside the transmission gear shafts speed up the shift by locking in the new gear, which instantly throws it out of the old one. The resulting feel of the shift is apparently similar to the long standing dragbike racers trick of the “auto” gearbox.

The Honda patented shift mechanism


In the dragbike modded box, the standard dogs on the gearbox are ground in the reverse direction to the way a road racer would “back cut” the transmission. Then with the aid of a modified shift drum, as a new gear is selected, the old gear jumps easily out of drive, with no noticable delay. One problem of this design is backing off the throttle makes the bike jump out of gear, not at all suitable for circuit racing.

What has any of this got to do with a 1960’s designed trail bike?

Honda’s patented method reminded us here at Motoaus of another “shaft selected” gear shift method. Back in the 1960’s and 70’s, a small Oregon US based company called Pabatco iimported a range of Japanese made trail bikes, the Hodaka. Mostly remembered for their quirky model names – the “Super Rat” and “Combat Wombat” perhaps the best ones – Hodaka’s had an unusual gearbox design.

The Hodaka shift mechanism


The gear shaft was hollow, and a plunger (1) that moved when you shifted, pushed or retracted a set of steel balls (2) through holes in the shaft (3) that locked the required gear (4) in position. This meant no shift drum or selectors were required, making for a compact light gearbox. Unfortunately this design didnt translate to faultless shifting. Whilst not a total disaster, many Hodaka’s, particularly the higher power models, suffered from jammed shifters, with some MX models like the “Super Combat” requiring contant fettling.

It isn’t hard to imagine a Honda technician remembering the Hodaka design as they pondered how to make the MotoGP bike shift faster. There really is nothing entirely new under the sun.

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