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Found: Brilliant Two-Chamber Pad Contact Adjust Concept for Hydraulic MTB Brake Levers

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tien hsin industries hydraulic disc brake free stroke adjustment design patent for mountain bike brake levers

Free stroke is the term used to describe how much lever pull you have on a hydraulic braking system before the pads actually start moving toward the rotor. Higher end brakes from most brands have a pad contact adjustment to let you dial in the free stroke, and the good ones actually provide a discernible effect. Avid has it, as do Shimano, Magura, Hayes, FSA, Formula, etc.

And all of them use a design that places the adjustment components inline with the fluid’s flow from the master cylinder into the hose. It’s worked so far, so what could possibly be wrong with that design?

FSA K Force SLK Hydraulic Disc brake601

Shown above on FSA’s K-Force brakes, the red dial allows for pad contact adjustment. Internally, it tends to move the piston’s sealing point further or closer to the port, changing the point at which fluid starts moving into the hose and, thus to the calipers to actuate the brakes. (cutaway photos of these brakes are here)

It works, but Tien Hsin Industry’s patent application claims this type of design introduces complexity to the assembly process and more seals and parts in a position vulnerable to leaks. The solution? Separate the pad contact adjustment system from the fluid flow. Here’s how they did it:

tien hsin industries hydraulic disc brake free stroke adjustment design patent for mountain bike brake levers

THI simply moved the free stroke adjustment dial to the opposite end of the master cylinder. Or, rather, they put the exit port for the fluid to enter the hose between it and the piston. Here’s how it works, based on the patent description:

The free stroke adjuster knob (yellow) turns the rod (pink), which slides the nut seal (purple) closer or further from the port between the first chamber (33) and the second chamber (22). As the brake lever is pulled, the piston (green) pushes the rod simultaneously until the nut seal hits the end of the channel and closes the port between the two chambers. Once that port is closed, the piston continues to move, sliding over the rod and forcing fluid into the hose. The fluid then pushes through to the brake caliper and moves the pads closer to the rotor, just like normal.

The secret to this design is the dual chamber system. Brake fluid sits in both, and the membrane (25) sits on the second chamber’s outside end to handle fluid expansion. When the brake lever isn’t being pulled, fluid can flow between both chambers. Once you start pulling the brake lever, the nut starts moving to close off the second chamber and thus force fluid into the hose. By turning the free stroke adjustment knob, you control how much the lever can be pulled before the pads start moving in the caliper. Here it is in action:

tien hsin industries hydraulic disc brake free stroke adjustment design patent for mountain bike brake levers

Click to enlarge. The patent was filed all the way back in 2012 and was just published October 7th, 2014.

Now, here’s the really interesting part: Tien Hsin could be considered FSA’s owner, depending on how you look at it. And the inventor on the patent is Jason Miles, an employee in FSA’s U.S. offices and engineer on their brakes.

We spoke with Herb Tai, FSA’s brake product manager, who told us: “We’ve got a number of new (rim) calipers for road bikes coming out for model year 2016. And we’re working to expand out hydraulic line up. The whole reason we got into hydraulic mountain bike brakes was to grow the technology, and the mountain bike brake market is already pretty crowded.”

Read into that what you will…

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edge
edge
9 years ago

must have pad adjustment…..AMEN.

Graeme Smith
Graeme Smith
9 years ago

I don’t care about ADJUSTING the amount of freestroke – I just want it to be sufficiently small… Shimano’s are perfectly acceptable to me but slightly less freestroke would not go amiss.

Von Kruiser
Von Kruiser
9 years ago

I’ve been using the FSA brakes since they came out. Pretty bitchen brake adjustment and modulation. Usually have my lever as far in as possible but now I can adjust the levers out a little more then usually do and make the pad contact super tight. The levers feel better and would have never used this lever position before. Easy to bleed, uses Shimano pad apparently, but I did use an Avid olive and hose barb when cutting the hoses (lost the original parts). Fit perfect but I’m sure it’s not recommended. Next time I’ll use their parts for bleeding. Seemed to bleed just fine with no issues yet (six months)… unlike my old Avid brakes which required bleeding all the flipping time. Got them super hot once or twice with minimal fade but came right back after hitting the flats for the next DH.

greg
greg
9 years ago

Formula’s separate, optional (and technically compatible with any dot fluid brake) is the simplest IMO. spring loaded piston, turn the knob to tighten the spring so the piston is bottomed out for immediate engagement, or back it off. you squeeze the lever, piston compresses, bottoms out, then pads move.
dont really know why people would want lots of free stroke anyway..,

John
John
9 years ago

DOT brake fluid? Pass…

gringo
gringo
9 years ago

TH / FSA are, as far as the end consumer is concerned one in the same.

SirEddy
SirEddy
9 years ago

I agree with the comments. I would prefer that free stroke actually move the pads away from the disc further to prevent rubbing. If I understand above correctly, it doesn’t actually change pad movement but rather that amount the lever moves before pads start to move.

That’s why I like servo wave in principle

FSA USA
9 years ago

Von Kruiser – Glad to hear you are enjoying the brakes and pushing them hard. Give us a call if you need any help with fittings in the future.

John – We also choose Mineral Oil over DOT for our brakes.

SirEddy – You are correct sir, in that, all free stroke adjustments currently on the market change only the amount of dead band or dead stroke before the system closes and starts building pressure. They have nothing to do with how close the pads (or caliper pistons) are in relation to the rotor (disc). Brake pad retraction and lever stroke is a balancing act. “Quick take up” systems, like servo wave, can allow for an increase in caliper piston retraction, but create a “knee point” or significant change in mechanical advantage and/or power within the braking process. We use a linear actuator or cam, so that the mechanical advantage of our system is consistent from the beginning of the brake apply all the way through lock up, as Von Kruiser noted.

George
George
9 years ago

I smell dot air travelling between the chambers, among with the fluid!!!!

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