I'm done with Shimano brake wandering bite point

Ah, Shimano brakes. There seems to be an unmitigated PR disaster plaguing them.

Most of us have no doubt hear about Shimano wandering bite point. A rider tells us of how happy they are to switch switched to another brand, pleased that they don't have to deal with Shimano wandering bite point. They're willing to spend more, even willing to be on 6-month long waiting list for Trickstuff brakes. A rider who has never experienced the issue says that they're avoiding Shimano brakes, since it sounds like a crash waiting to happen, perhaps interested in the next closest thing (e.g. TRP). It's been talked about for years, but has Shimano not offered a fix?

This is my attempt to share my in-depth technical view of why the bite point wanders on Shimano brakes.

Generally, I get the gist that people refer to the feeling of meeting lever resistance earlier (or later) than expected, as wandering bite point.

When the brake lever basically pulls all the way the grips, generally air is suspected to be in the system. Temp fix: pump the brake lever while the bike is upright (air floats up into the reservoir and out of the line, making the lever firm up earlier). It's only temporary because the air can get back into the system if the bike is flipped/placed in a way in which the affected lever is closer to the ground than the caliper (e.g. upside down). Long-term fix: perform a brake bleed.

When the brake lever firms up earlier than expected, this is generally something uniquely felt with *some* Shimano brakes. Some people with Shimano brakes claim to never experience this. Some claim it goes away with a good bleed, but may come back within 4 rides. I can get it to happen if I drag brakes, let go of the brake partially, and squeeze again quickly.

Why doesn't this happen to other brand's brakes? I highly suspect that this wandering bite point is related to Shimano's Servo Wave tech. More specifically, I blame binding/friction in the Servo Wave "guides", causing it to be slow to retract.


This is the Servo Wave mechanism on an XTR lever. The leverage ratio between the lever blade and the other end is maybe ~5.5:1 (red) to start, meaning that there's less leverage but more travel (pad quickly moves to contact the rotor, with less clamping force). The leverage ratio then gets adjusted to ~8.5:1 (blue), meaning there's more leverage (higher clamping force at the caliper, for any given finger pressure at lever).

On lower end levers, the Servo Wave cut-out guide is replaced by plastic guides.

^ Shimano Brake lever disassembled. Image source: https://nuxx.net/blog/2020/10/25/rebuilding-shimano-slx-bl-m7000-brake-levers/

I suspect that these plastic guides get mineral oil leaked onto them and feel well lubed for a short while, but then feel bad as that oil attracts muck, resulting in a bleed being able to temporarily able to fix it.


To speculate why the brake levers firm up sooner unexpectedly, I have a hypothesis--because the Servo Wave can be slower to retract than the lever, if you let the lever retract and then quickly pull it, the Servo Wave bushing can catch on the low leverage end of the lever (red circle). If the Servo Wave is very mucked up, it can stick to any part of the lever's hooked part, resulting in an inconsistent brake point.

That's it. That's all I got. As far as I'm concerned, the case is closed and I'll be careful about getting the Servo Wave mucked up on my Shimano levers. I'll cover that part of the lever during a bleed, and will appreciate how I can ride in fairer weather where the muck that my tire sends flying up in the air doesn't get carried in there by chance. I've seen these guides break, so I don't recommend using chemical cleaners (e.g. brake cleaner) to spray in there, as the plastic may become brittle.