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I have Tektro HD-M276 Hydraulic Brakes that were recently spongy (front brake).

After bleeding the system and topping the fluid off, the bite was much firmer, but when I test rode it, the braking power was still extremely weak.

The pads were relatively new, but I sanded the top layer in case there was glazing. I also cleaned off the rotor, but none of this changed the braking power.

When I tried to get a little more air out of the tube, I noticed that the handle would suddenly become spongy when I turned/tipped the handlebars different directions.

Does anyone know what's going on and how I can fix all of this?

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    Sounds like the bleeding might have helped but there's still bubbles in the line ? Check closely the hose and joints for weepage of the fluids, which indicates a crack.
    – Criggie ♦
    Sep 5, 2022 at 22:58
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    Any chance you got oil on the pads? Is the caliper bleed port firmly closed? Did you do anything to the caliper pistons during the bleeding process?
    – MaplePanda
    Sep 6, 2022 at 1:12
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    If you sanded the pads and cleaned the rotors you need to bed-in the pads again.
    – Paul H
    Sep 6, 2022 at 22:17
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    On re-reading one thing confuses me. You "bled the brakes and (then) topped off the fluid" whereas those two things are part of the same process. Could you have introduced air by adding fluid after bleeding? Remember the bleed cup has to be at the top of the system so air can rise into it.
    – Criggie ♦
    Sep 6, 2022 at 23:57

2 Answers 2

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When you mentioned that that the brakes became spongy again after tipping and turning the handlebars some, that is a clue that there is still some air in the system, and you will need to go through the bleeding process again.

I have seen this occur on some Shimano XT brakes I have and although I could “pump them up” and alleviate the spongy feeling, after a short time the spongy feel would return. Spongy feeling is air in the system somewhere. Doing a proper bleeding “by the book,” i.e., following the dealers manual, resolved the problem for good. Proper bleeding takes a little patience and attention to detail. A little air can be let back in if you are not careful.

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Assuming the bleed was done properly and there is no more air in the system, it could be that the brake hose is damaged. This would allow the brake hose to expand on pressing the brake, effectively reducing the pressure on the pistons. That could explain why turning the handlebar would affect the braking power as well, if the hose is damaged near the handlebar.

Brake hose bulging under pressure

See this video as an example on how the brake hose damage can affect the braking power:

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  • That is a reasonable reason. Is it usually/always visible/detectable to the naked eye? Always good to add another bit of diagnostic telemetry to the mental tool box.
    – Ted Hohl
    Sep 7, 2022 at 13:37
  • Hard to say in general terms. However I would expect that if it's sufficient to affect the braking power, it's probably visible to naked eye.
    – Superman.Lopez
    Sep 8, 2022 at 3:14

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