Brake modulation - Mechanical Disc Brakes

A friend of mine just bought this bike:
It has mechanical disc brakes and he mentioned braking takes enormous effort. I told him that's because the brakes have no modulation and perhaps something like a Shimano SM-PM70 modulator might work. But I've only ever installed those on older mountain bikes with V-Brakes. Does anyone have any experience installing this kind of modulator onto a disc brake system? (would this even work?)
Thanks much!


  • davidof
    davidof Posts: 3,065
    edited November 2021
    decook said:

    A friend of mine just bought this bike:
    It has mechanical disc brakes and he mentioned braking takes enormous effort.

    Probably something sticking in the system: cables, outers, brake calipers.
    Modulation is the ability to precisely dose the amount of braking letting you ride the fine line between 99% braking force and lockup.

    If the bike is new, take it back for a service.

    If second hand, service the brake parts as above.
    BASI Nordic Ski Instructor
  • First.Aspect
    First.Aspect Posts: 16,031
    How is a brake modulator supposed to help if the problem is not enough braking is available? All it does is make the brakes even spongier.

    Seems like a colossally stupid product anyway - right up there with oil to reduce the sound of squeaky brakes.
  • lesfirth
    lesfirth Posts: 1,382
    I have no experience of using one of these "modulators" but my understanding is that they are intended to help prevent you locking the front wheel when you apply the brake too hard.. They will do nothing for your friend who seems to have the opposite problem .
  • pilot_pete
    pilot_pete Posts: 2,120
    Your post doesn’t say what brakes the bike has. The linked picture shows TRP Spyres which when set up properly are absolutely fine. However, they do go ‘out’ of optimum and require regular servicing/ adjustment.

    If the bike is new they are likely to have bedded in and will need re-adjusting to allow for the (effective) shortening of the cable outers through all the bedding and settling in. If the lever pull has increased, and especially if it’s touching, or nearly touching the bars without full braking being applied this is the likely cause.

    It could be that they weren’t set up correctly in the first place - I find you need to get the cable clamped at the caliper right or your lever will not pull enough cable to fully actuate the brake.

    However, if all that is good you need to check the pads and rotor for contamination. If the pads are contaminated there is a strong possibility you will not get full braking force applied to the rotor and thus lack stopping power. This is more likely if the bike wasn’t new.

    With correctly set up, and bedded in pads you should be able to lock the wheels up with TRP Spyres. This shouldn’t take excessive brake lever force to achieve. Your idea about a modulator is not the solution you are seeking. Get the brakes working right and all should be good.
  • Sort the brakes first! I have had cable disc brakes (Avid) and they work fine.