The cat is outta the bag so to speak now that Hayes has revealed the internals of the new Prime MTB brake system. If you recall my previous article, I mentioned that some of the technology was borrowed from motorsports and as you can see, this unit features a high tech moving master cylinder that can change its position relative to the cam (brown). This allows the rider to adjust pad position without loosing stroke. Below is a video with the Prime cam in action showing you the movement of the unit.
As you can see there is a lot going on in that small master cylinder. The video below includes a good explanation about how the master cylinder works and talks about some of the features of the Prime braking system.
One of the big innovations with the new master cylinder design is the improved flow of fluids within the system. For those who like to ride fast and hit the brakes hard, the improved flow keeps the brake fluid cycling regularly, preventing it from heating up too quickly and reducing the chance of expansion. Brake fluid expansion causes the pistons to move towards the rotor which in turn causes the pads to drag. Dragging pads slows you down slightly and builds up heat in the system (making the problem worse). Bottom line: the Hayes Prime “brakes” the hot fluid cycle.
Prime brakes also do away with the traditional port timing hole which is used to allow fluid to return to the reservoir and compensate for pad wear. The new design, due to the absence of the timing holes, increase seal life. On most brakes, the delicate seals on the timing holes wear over time – basically every time you squeeze the brake lever. With the holes gone there is a smooth bore, thus a longer seal life.
You’ll also notice that the master cylinder piston is hollow – this is what enables increased brake fluid flow. To top it all off, the good folks at Hayes even included an updated and redesigned titanium push rod to further reduce side loads on the piston (increasing piston life).
Well folks that’s all I got for now. As always, if there’s anything new and exciting I will keep you posted – cheers!
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