The engine has an external cetrifugal clutch (primary clutch) on the crankshaft. A drive belt connects the primary clutch to the secondary clutch which is connected to the upper gear of the chaincase. The chaincase has a chain connecting the upper gear to the lower gear and the lower gear is connected to the driveshaft which has interlocking drive cogs mounted on it that drive the track. Most moden sleds have a lever on the left handlebar to activate the hydraulic disk brake attached to the top gear of the chaincase (external to the chaincase on a short shaft).
When I broke down in the mountains, the end of the driveshaft sheared, essentially disconnecting the chaincase with associated brakes from the track so the track could freewheel regardless of applying the brakes or reving up the engine to accellerate.
So its not really brakes, like a jet ski? edit, wait so a little better its actually stopping the belt?
The brakes are between the belt and chaincase in the driveline. That belt on the 2 clutches allows the engine to freewheel at low RPM for starting and idling. The faster the RPM, the primarly clutch starts to engage and squeeze the sides of the belt to drive the seconary clutch.
The primary squeezes harder on the belt with RPM. The two clutches provide unlimited ratios as the belt is squeezed outward by the primary clutch and pulled deeper into the sheaves of the secondary clutch. Nothing like a jet ski drive, more like a golf cart drive but handles much much more HP and allows the sled to go from O to +/-130MPH (on high performance sleds with 120HP and up).
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