The external reverse gearbox setup found on most 150cc GY6 buggies (and the buggy depot reverse kit) is actually a rather simple piece of machinery compared to most other gearbox designs. The brands of 150cc buggies that have this style of gearbox include but aren't limited to: Dazon, Blade, Carter Bros, Twister, SunL, Awesome Buggies, and several more. Here we will run through the basics of reverse operation. It is best if you are reading through this article while disassembling a gearbox real-time.
Important things to note:
- There is no neutral in this style of gearbox.
- The default mode of operation is FORWARD.
- Forward is 1:1 ratio.
First, lets go over the components of reverse. The major parts are the: shifter handle, reverse cable, output shaft, and gearbox. The handle is connected to the gearbox via the reverse cable.
The reverse cable is connected inside the gearbox to a yoke which is responsible for pulling an internal planetary gearset into REVERSE. A large spring is also held on this yoke to return the gear set into FORWARD position when tension on the cable is released. The gearbox receives power from and physically rests on the transmission output shaft, which turns due to the workings within the engine and transmission.
Going into the gearbox, here are the major components:
1. Ring gear (The ring gear is the gearbox half that the external 16 tooth drive sprocket bolts to)
2. 3x Planet Gears & Carrier
3. Sun Gear (Output Shaft Gear)
4. Shifting Yoke
5. A few spacers and a bunch of grease
Now that you have a basic understanding of the internal and external parts, lets get into how the gearbox transmits power.
It all starts with the transmission output shaft, which sticks out of the final transmission case. When you press the "GO" pedal, this shaft turns clockwise. The output shaft enters the gearbox and meshes with a gear unit, which we will call the "Sun" gear. This sun gear rests in the center of the gearbox and meshes with both the planetary gears and a set of "dogs" (gear teeth) on the planetary gear carrier. This is the critical step. The difference here between being in FORWARD and being in REVERSE is simply a matter of whether or not these "dogs" are meshed with the output shaft. When the dogs are disengaged from the output shaft gear, the planetary gears will "lock up" and the entire unit (all components from the output shaft to the ring gear) rotates in FORWARD mode. When the gearbox is shifted into REVERSE mode, the carrier teeth engage and allow the planetary gears to spin - causing the ring gear to rotate in the opposite direction. When this happens, the inside of the gearbox looks very similar to this: