Djangodog
Well-Known Member
- Region
- USA
- City
- Claremont, NH
Disclaimer, I am not a bicycle mechanic. I was a mechanical engineer and I have built high end mountain and road bikes, including the wheels, but I am not a professional bicycle mechanic and I make no claim to be an expert.
My wife and I both have Yamaha Cross Cores. Both had spongy feeling rear brakes. Having had a Specialized Crux Cyclocross bike years ago, (SRAM Red with Mechanical Discs), I knew that this was not how the brakes had to feel. Typically, a rubbery feeling brake lever is a cable issue, not a caliper issue. I removed my chainrings to access the clips that secure the derailleur cables, removed the motor mount screws and raised the motor out of the frame, (the bike was inverted). The cable housing exits the chain stay and turns nearly 90 degrees to go over the motor and then down the front of the motor to turn nearly 90 degrees again so that it can go up the down tube. Basically, as the cable is tensioned it is binding against the tight bends, (wanting to pull straight), and the force on the lever is absorbed by the cable against the lining. This doesn’t happen with the Hydraulic brakes on the other Yamaha Ebikes because the brake fluid can flow as long as there is not a restriction. A kink would be a very bad thing with a hydraulic system.
Long story over, I pulled in enough cable housing so that I could route the cable over to the right as it went over the motor back to the left as it went back down, (when I first went to remove the motor from the frame it felt like there was a spring pushing it, that spring was the brake cable). I was amazed at the difference in braking. No more spongy lever or vague braking.
If your rear mechanical disc brake feels rubbery, be aware that the issue is most likely either the cable or that the static brake pad is too far from the rotor, (or a combination of the two). In our cases, rerouting the cable made a night and day difference.
My wife and I both have Yamaha Cross Cores. Both had spongy feeling rear brakes. Having had a Specialized Crux Cyclocross bike years ago, (SRAM Red with Mechanical Discs), I knew that this was not how the brakes had to feel. Typically, a rubbery feeling brake lever is a cable issue, not a caliper issue. I removed my chainrings to access the clips that secure the derailleur cables, removed the motor mount screws and raised the motor out of the frame, (the bike was inverted). The cable housing exits the chain stay and turns nearly 90 degrees to go over the motor and then down the front of the motor to turn nearly 90 degrees again so that it can go up the down tube. Basically, as the cable is tensioned it is binding against the tight bends, (wanting to pull straight), and the force on the lever is absorbed by the cable against the lining. This doesn’t happen with the Hydraulic brakes on the other Yamaha Ebikes because the brake fluid can flow as long as there is not a restriction. A kink would be a very bad thing with a hydraulic system.
Long story over, I pulled in enough cable housing so that I could route the cable over to the right as it went over the motor back to the left as it went back down, (when I first went to remove the motor from the frame it felt like there was a spring pushing it, that spring was the brake cable). I was amazed at the difference in braking. No more spongy lever or vague braking.
If your rear mechanical disc brake feels rubbery, be aware that the issue is most likely either the cable or that the static brake pad is too far from the rotor, (or a combination of the two). In our cases, rerouting the cable made a night and day difference.
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