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I have an oldish bike equipped with Shimano LX components. The brake levers have a L•H adjustment (see photo below). What could be its purpose? And as a bonus question, what were the drawbacks, as no modern brakes have a similar adjustment?

The documentation I could find calls it "power adjuster", but there's a part I miss: I would understand that the pure braking power depends on the levers, themselves defined by the length of the different levers/the relative position of the different pivots, that remain constant regardless of the "power adjuster" position.

Shimano LX Brake lever

enter image description here

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2 Answers 2

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That's for changing the cable-pull of the lever.

L will be a long-pull for V brakes or similar. The cable end-stop is further from the pivot, and therefore travels through a longer arc.

H pulls less cable overall, so is for caliper brakes. I don't know why it is labelled "H".

The downsides are added weight and complexity, and a strange failure mode for the brakes if the mount shifts during a ride. Simply having dedicated long or short pull brake levers installed removes a point of failure. It's not like a rider would need to adjust this ever while riding.

And cynically, Shimano get to have more SKUs in their catalogue.

This is not the same as "Servo wave" which also has a slot arrangement in the lever, but that is intended to pull cable faster initially, and then slower+harder once the pads bite.

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    It's interesting that it doesn't appear to be a binary, but instead either a continuous adjustment or 3 positions. So they may sell on tuning, which would make a little sense with cantilever brakes. Is suspect L & H are low and high mechanical advantage - terminology chosen from the point of view of the engineer rather than the user
    – Chris H
    Commented Nov 20 at 11:51
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    Answer accepted, but with a "but": I doubt that the intent was to make levers that were compatible with caliper brakes to start with (although you get a variation in the perceived power by changing the cable-pull), I'd rather imagine it's an unintended consequence. Thanks!
    – Rеnаud
    Commented Nov 21 at 17:16
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According to the Shimano documentation for the LX BL-M570 brake lever:

The M570 brake system is equipped with a power adjuster in the wire hooking unit of the ST-M570/BL-M570 brake lever which allows the rider to change the relationship between the brake input and output. If this power adjuster is moved, the braking force will be dramatically increased, so that a high level of braking performance can be achieved from only a small amount of lever movement.

"change the relationship between the brake input and output" is a little cryptic but it's all the explanation the document gives.
Somehow a pivot point is moving to change leverage.

Picture of brake lever instructions

The brake cable is routed a little different than usual.
Brake cable routing picture
So So, "L" means low braking power
"H" means high braking power

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