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Well, I bought a bike called "Iron Horse" and the bike has front and rear mechanical disc brakes. The brakes, upon inspection, have no writing at all (The manufacturer was too scared to put their brand name on them...).

Since day one, they have been absolutely terrible; Back brake only locks the wheel when I let weight off and the front brake would sooner have me hit a car in front than actually do any noticeable braking. I'm aiming to be able to lock the front brake to the point that pulling the lever makes me flip the bike like on my road bike, and the back brake cause wheel lock-up with merely about 30% action.

Cabling routing and length seems fine to me, brake lever is not bending, nor is mount for it. Caliper mount is nice and sturdy and does not move no matter how much I clamp on the brake. The pads are not half-inserted, nor are they worn out. They're brand new! Pads are not contaminated, pads are equal distances from the rotor on either side of the caliper, cable is tensioned so that the brake is pulled 15% of it's total action before pads contact the rim. The rotor is arrow-straight. The wheel hub where the disc attaches is not damaged in any way nor weakened considerably.

I've never worked on disc brake bikes, so my question is; Do all mechanical disc brakes have this much difficulty stopping? Is there something big that I'm missing? Is there a particular thing causing this? Could the pads be a bit duffed? Is there any type of pad I should try out on my bike (different compound, etc) or any specific modifications I should try?

And finally, are there any really, really risky bodges that I can try out to immediately bolster braking power? (Anything I do on the bike is not your fault, but my own.) Give me a really risky method of making the brakes powerful instantly and I'll give it a shot! :P

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    Your pads may just need bedding in. What model of Iron Horse bike? – Argenti Apparatus Jan 10 '18 at 0:40
  • Iron Horse Revolution, though it's not the kid's size one; it's the 24" frame. I'm tiny, lol. I don't think it could be bedding in; my road bike's brakes bed in after a few minutes of riding. I've been torturing the brakes on the Iron Horse to get it to do ANYTHING. I wouldn't be surprised if I snapped the brake levers off at this rate! :P – yollooool Jan 10 '18 at 0:54
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    How sure are you that the pads aren't contaminated? Sounds exactly like that's the problem. – alex Jan 10 '18 at 3:51
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    New outers were required to fix cable discs on my sons bike. Without putting in new outers as well as inners, I hesitate to eliminate cable problems. – mattnz Jan 10 '18 at 8:29
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    Interesting that you used the word knackered in relation to a Iron Horse bike – Argenti Apparatus Jan 10 '18 at 12:50
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Usually what causes this (literally no braking, firm lever feel, lever nowhere close to bottoming) is an error in brake setup or adjustment wherein the brake caliper's armature is being pulled to the end of its range of motion before full braking power is reached, or in some cases before any braking power is generated.

This can happen either as a result of incorrect setup or by compensating for pad wear exclusively by way of the cable barrel adjuster without adjusting the stationary pad.

To determine armature bottoming is the problem, see if you can use your fingers to directly push the armature as far as it can go. If possible, try turning the wheel with your hand while doing so to ascertain no braking is happening. Or just undo the brake cable anchor; if the arm was obviously near the end of its range of movement, that's probably been the problem.

Most mechanical brakes perform their best when adjusted so that the armature starts out near the beginning of its range of motion. The mechanical advantage characteristics of the brake change throughout its travel. So when setting up a brake, always try to get the arm as close to that point as you can while still having all the slack pulled out of the cable.

Usually adjusting a generic mechanical disc brake with this issue is going to involve undoing the cable anchor, possibly installing new cables if the old one either won't be long enough with the arm starting down in the right spot or has more of a crimp than is safe to have in the system (usually mechanical discs are pretty good about the latter point), loosening the caliper mounting bolts, dialing in the fixed pad adjuster, re-positioning the whole caliper more inbound towards the wheel such that the moving pad starts out closer to the rotor, then re-fastening the cable anchor and doing final adjustments.

For a brake with pad adjusters for each pad, resetting the barrel adjuster and extending the moving pad in may fix the acute problem, although it probably won't be enough to get the arm back to its intended starting position.

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    "reset the barrel adjuster" I hate to think how many times that one has caught me out. – Criggie Jan 10 '18 at 8:58
  • "Most mechanical brakes perform their best when adjusted so that the armature starts out near the beginning of its range of motion. The mechanical advantage characteristics of the brake change throughout its travel. So when setting up a brake, always try to get the arm as close to that point as you can while still having all the slack pulled out of the cable." This makes a lot of sense to me. Having been working on cars for a while, the parking brake on disc brakes for cars work the same way as brake discs on cars, and those have to be set as stated. I'll have a go at trying this fix soon! – yollooool Jan 13 '18 at 21:17
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    Having checked on the bike, this worked perfectly; Loosening off the caliper and caliper carrier bolts, I proceeded to place a piece of paper within the gap of the rotor and the braking pad material. Following that, I clamped down on the lever and tightened the static-pad adjustment screw until it started bringing the lever's 'biting point' towards about 50% action, before tightening down the caliper carrier and caliper mounting bolts. The brakes aren't nearly as powerful as that on my road bike, but they can actually raise the back end of the floor and allow me to skid a good distance. – yollooool Jan 14 '18 at 17:41
  • I will also add that I had used a bit of grease on the guide along the caliper itself that allows the cable to channel neatly when you've let go of the lever. I think this had absolutely no affect on the braking whatsoever, though it has reduced residual brake drag/release delay after braking, allowing the cable to slide along it freely. The pad slightly touches the disc on the static pad side, but I can live with that sound in exchange for the increased braking power. Hopefully I'll be able to attack some stairs and some off-roading! Thanks again, everyone for all the help! – yollooool Jan 14 '18 at 17:45
  • Grats on making it work. I will note that putting grease at that spot makes me a little nervous of the possibility of it one day migrating, with the help of rain and muck, to the braking surface. – Nathan Knutson Jan 14 '18 at 20:47
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You've eliminated mechanical/cable problems, and the levers sound fine.

There's some braking effect, so the pads are moving on lever pull.

There are 3 possibilities:

  • the brake pads are terrible, either cos they're bad or they have been contaminated
  • The rotors are contaminated (which means pads will be too)

Clean them with IPA and possibly replace the front pads.

I doubt the pad gap is too generous because your lever is not bottoming out on the bar.

BUT another thought - a cable-operated caliper is normally one-sided. So one brake pad is fixed and supposed to run very close to the rotor. The other moving pad subtly bends the rotor into the fixed pad. You may need to confirm that the non-moving pad/rotor gap is nice and small.

If its big, loosen the two caliper mounting bolts a bit, shim between the rotor an non-moving pad with a sheet of paper or similar, then hold down the lever while tightening the two bolts. Then extract shim. Your brake may have a lot of room on the other side now, so you need to take the slack out of the inner cable at that point.

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    I think you're onto something with adjusting the fixed pad. The (decent) cable disc brakes on my tourer are fairly sensitive to this adjustment. Mine have a fair amount of adjustment built into the fixed caliper, operated by reaching through the wheel and turning the back of the fixed caliper. Of course the OP's no-name brakes probably lack this, but it depends who they've copied. – Chris H Jan 10 '18 at 7:02
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    But isn't for example the Avid BB7 recommendation to have the pad space exactly the other way round, so that the moving pad is closer to the rotor than the fixed pad? Which is totally counterintuitive because it causes the rotor to be bent against the fixed pad. – zedoo Jan 11 '18 at 19:25

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