Article Brake Caliper Action

[jfheath]

An animation of the action of the brake caliper of a Honda ST1100 and ST1300. It is obvious that the pistons move out to the right to press the outer pads against the brake disc/rotor. It is not obvious, unless you have thought about it, that the entire caliper must be free to move to the left. This equal and opposite reaction to the pistons moving is only possible if the slider pins are clean, the pads are inserted correctly and the pad springs are clean and are properly seated.

All 3 calipers work in the same way, but I have drawn it as if looking from the rear of the bike at the rear caliper.

 

[klaproth]

Wow....way cool! Very well done. Although I could picture it in my mind, this makes it even better.

 

[CYYJ]

Superb animation, thank you for creating it.

I did not know that the whole caliper assembly moved when the brakes were applied. It makes sense now that I have seen it in the animation, but it's not something I would have thought of on my own. Before seeing the animation, I thought that only the pads moved.

Michael

 

[Mellow]

Would be cool if someone could mount a gopro in that area and show the action as well.. another time I wish I still had my ST..

 

[Upt' North]

Thanks John, nice.
I think in a previous life I found this is why when fixed calipers are used you need floating discs, and with sliding calipers fixed discs can be used. But don't quote me on it.
I don't think a camera down there would show much at all, in real life the movements are very small. As in miniscule.
Upt'North.

 

[ReSTored]

Great animation and illustrates, literally, why proper brake service is not just cleaning up pads and pistons but all components of the system.

 

[John OoSTerhuis]

I thought the fact that the caliper body moves (in a single-action/‘piston(s) on one side’ design) was self evident/understood (how else does the other pad contact the rotor?).

What I suspect is the least understood action/function of brake calipers in general is that of the piston seals. Over many thousands of applications, over long periods of time, we confidently enjoy slowing our wonderful STeeds, relying solely upon the inherent elasticity of those simple little rings. If they cannot return to their normal rectangular cross-section, having been deformed as they grip the piston when it’s extended (parallelogram), when hydraulic pressure is released they’re malfunctioning. It’s not very much movement, but if it doesn’t the pads continue to grip the rotors. If underway at the time, the bike’s inertia can overcome the friction with resulting pad and rotor wear and heat. If in the garage when the piston is extended, it can effectively lock the brake and immobilize the ST. BTDT

So... change your brake fluid often and inspect the function of the pistons whenever you have the wheels pulled. You should be able to push the pistons in with your fingers. Piston seals R&R should be a routine maintenance item depending on age, mileage, and useage. YMMV

Edit: to be clear, the common cause of pistons not fully retracting is corrosion buildup in the fluid seals’ grooves in the caliper body, resulting in the seals pinching/gripping the pistons too tightly. Hydraulic pressure can overcome the abnormal constriction and extend the pistons, but when released the piston doesn’t retract.

John

 

[wjbertrand]

Thanks John, nice.
I think in a previous life I found this is why when fixed calipers are used you need floating discs, and with sliding calipers fixed discs can be used. But don't quote me on it.
I don't think a camera down there would show much at all, in real life the movements are very small. As in miniscule.
Upt'North.

Most fixed calipers are double acting, i.e. there are two or more opposed pistons squeezing the rotor. In a double acting design there’s no need for the caliper to side as the pads wear since there’s a piston on each side to accommodate that.

A single action caliper cannot be rigidly mounted or there would be no means to accommodate the wear of the pad opposite the piston.

Floating or rigid rotors can be used with either design. Floating rotors are mostly designed to accommodate radial expansion as they heat up, less so for side to side movement and certainly not enough side to side movement to accommodate pad wear in a single action caliper design.


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