Flappy front (mechanical disc) brake

[ravenbait]

I've got Rever Havit on my Hurricane. The rear is super: crisp, effective, reassuring. The front, OTOH, is soft and flabby and I have to haul on the front lever so hard it often gets stuck against the bars. I've tried the tension screw (it achieved precisely nothing), and when I adjust the cable length the tolerance between squishy and rubbing is nanometres. Clearly the brakes are not just rubbish brakes, because the rear is fine.

Is there a trick to setting up mechanical discs? Please don't tell me to fit hydraulics instead, it's not helpful.

The Hurricane has internal cable routing, if that makes a difference. I can't make the barrel adjust turn, even using pliers -- the only way to adjust tension is to undo the cable at the piston and adjust it there.

Sam

[Cudzoziemiec]

Does the barrel adjust turn the other way, ie out? And presumably the adjuster works okay on the rear?

[LittleWheelsandBig]

Are the pads contacting the disc squarely or is one edge touching before the other? If contacting at an angle, the brake will always be spongy.

Is the disc running true? A wobbly disc means less pad clearance.

Are you using ‘compressionless’ brake cable housing? That noticeably helps for the tight clearances of cable disc brakes.

[ravenbait]

I've only done a bit over 1000km on this bike, and it has been like this since new. I haven't disassembled it yet to see if the pads are contacting strangely. I have no idea about the cable outer specs.

The adjuster moves not at all. It's fine on the rear.

Sam

[LittleWheelsandBig]

It is commonplace for disc calipers to be mounted pissed, often because the mounting has excess paint or hasn’t been properly faced.

[ravenbait]

I think facing is outwith my skill set and tool catalogue.

Sam

[LittleWheelsandBig]

Not many bike-shops have disc brake mount facing tools.

[Cudzoziemiec]

You could try loosening the mounting bolts, clamping on the brake lever, then tightening the bolts with the lever clamped down. But if the adjuster doesn't turn at all, there's something broken (or missing?) inside.

[ravenbait]

I think there just isn't anywhere for the outer to go, and that's why the adjuster won't turn. It's only about 3" before it goes inside the fork, and I think it's just binding.

Disc looks true, not wobbly.

I'll try loosening it off. I have some fancier brake pads to fit anyway. I was just hoping there would be something obvious to try.

Sam

[Dickyelsdon]

So this is apparently a dual action mechanical, meaning both pads move towards the rotor on action (many cable only have one moving pad, resulting in mixed performance).

First things to check; operation
are both pads moving equally and smoothly?  You can take the wheel out and pull the lever a few times to check.
Are the pads installed correctly? check if youve replaced the pads, easy to get something wrong.
Is the cable binding? (does it feel bad when pulling the lever with the wheel out)
Is the outer properly seated at both ends? it should have a straight run into the adjuster, if its wonky then it will try to straighten with tension and give a mush feel.


Next; setup
With the wheel back in, both pads should be equally spaced from the rotor and perpendicular. Any misalignment will be bending the rotor instead of trying to grab it.
Are the pads wound in/out equally? there look to be adjusters, match each side, these are for wear not bodging installation.
Is there a sensible amount of movement in the lever before the pads contact, use the adjuster to match the lever travel with the rear brake lever. If you cant move the adjuster then you need to get that fixed. Remove the caliper and see if you can free up the adjuster or cable outer, whatever is stuck.

[ravenbait]

Thank you. I will go through this list at the weekend. Super helpful! 

Sam

[ravenbait]

Thanks for all your help. Front adjuster issue resolved by slackening off the brake cable, which gave me enough slack to wind it out a couple of turns -- it was pressed so hard against the stop that the barrel couldn't turn. Also, pulling the cable outer through the fork a bit more helped a lot

Realigned the brake and made sure the pads were moving equal distances.

It's a lot better now. Still not perfect, but a lot better.

Thanks again.

Sam