Bike mechanic can't fix my brakes

Question

Every caliper or V-Brake bike I have ever touched had fully functional brakes. Even if the pads were completely run down and steel was rubbing against the aluminum rim, if you applied enough pressure to the brake lever, you could easily lock up the front wheel.

I bought a gravel bike last year with horrible cable disk brakes and brought them to my bike mechanic. He replaced the clamping unit thing, which improved the braking but was still magnitudes worse than the worst V-Brake or caliper I've ever used. And I'm telling you, I've pulled completely rusted, damaged mountain bikes out of rivers that did a better job braking after a bit of fixing. It is impossible to lock up the front wheel on the gravel bike.

Now I got myself an Oolter Torm S e-bike just this week with brakes even worse than the original ones on the gravel bike. The front brake would somewhat slow the bike down in the beginning, but now, after 90km, they literally don't work anymore. I can pull the lever with maximum force and going downhill a 7% gradient, my speed does not decrease. The disc has blued, which signifies temperatures above 300C, and after pulling the brake with maximum force, the brake pad actually sticks to the disc and wont loosen until you reach and push down on this thing:

I'm better off sitting on the top tube and braking with my feet than pulling the brake level on both these bikes.

Both of my mechanics said they can install hydraulic disc brakes on my gravel bike, but they will need to replace everything, including the lever, which will cost me upwards of 500$ (on a 650$ bike). He said if I'm not willing to switch to hydraulic brakes, I will have to live with what I've got as there is no way to improve them. And there is no way to attach rim brake on the gravel bike fork. I feel like I'm being cheated.

I don't get it. The cheapest, crappiest V brakes will send you over the handlebars if you apply enough pressure, but here I am with disc brakes squeezing the lever with everything I've got.

I've got 2 bikes with brakes that don't work and both my mechanics say "Cable disc brakes are like this". Because of this I was actually tempted to ask "Do cable disc brakes actually work" lol.

Answer 1

If the pads are sticking to the rotors on hard braking, they're probably resin (or semi-metallic, which is resin-based), and probably ruined. The rotor may be past repair at this point too.

I'd start by fitting sintered metal pads and new rotors (ensure they're compatible with metal pads), and bedding them in carefully. This is all DIYable. When you fit the new components, and before bedding in, ensure the caliper is centred and square to the rotor. This depends on the exact design of the caliper but in general will involve loosening the mounting bolts, then retightening them with the lever pulled (e.g. by a strap). You'll probably (almost certainly on the one pictured) need to set the fixed pad position first. This is done working through the wheel. You may need to iterate caliper centering and pad adjustment a couple of times. The fixed pad should end up a fraction of a millimetre from the rotor when ready to use. Then the moving pad should be a similar distance, set by the cable clamp screw and barrel adjuster. Setting the caliper up is best done with new pads.

Answer 2

Cable-actuated disk brakes can work fine. There's clearly something wrong here.

The rotor getting hot means that friction is happening. I'd start by removing the caliper, remove the pads and inspect. If you could give us photos of the brake pads may be helpful.

Then I'd clean and deburr the caliper. Anything that is a rough edge should be gently filed to reduce friction. The caliper should be reliably opening itself under the pressure of its internal spring.

Also, true the rotor. Minor bends can cause it to wobble. Personally I use a dial indicator and a large spanner to adjust the rotor. Yours has overheated, and that may have "lengthened" the circumference leaving your rotor with a permanent wobble. If this is the case, you need a new rotor.

The rotor may also be glased/glazed since it has got hot - that might be removed with sanding but if its too pronounced then again replacement.
If you do replace the rotor, go for something with a bit more mass - your pictured one looks like a lace doily and has limited capacity to absorb heat. Might be appropriate for a race bike, but for longer downhills you want more capacity.

Next, reassemble then adjust the caliper on its mounts so it is just missing the rotor. Most cable-actuated disk calipers are single sided and have a fixed pad on the inside which can be adjusted for pad wear but doesn't move as you brake. This pad should be barely-missing the rotor.

The moving pad can be adjusted by the same cable-lengthening barrel adjuster that a rim brake or derailler uses. Again it should just miss the rotor.

Check the rest of your cabling too - ferrules should be firmly in the sockets etc, just like rim brakes.

Note that disk brake pads wear quite quickly compared to rim brake pads. If you ride hard and stop fast, they can disappear astonishingly quickly. Mud and abrasive sand and road dirt in the rain can eat them.

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The last option is to replace the whole brake assembly with a hydraulic. That's not an immediate panacea because there are fresh problems, like bleeding brakes.

I replaced the front brake on my `bent with a bottom-entry-level shimano flatbar hydraulic MT-200, which came as a complete pre-bled set and the difference was definitely worth it. Your quote for replacement probably includes labour, and doesn't say what parts they've specified. Though for a gravel bike it might mean drop-bar hydraulic brifters which relate to your gearing as well.

Answer 3

Your mechanic is wrong that there is nothing that can be done to improve your cable disc brakes, but there would still be some expense involved. In Cyclingtips' 2022 field test, they reviewed a number of bikes with cable disc brakes. Some of them can work well. However, some of them can be tricky to set up, and it appears that bikes with cable disc brakes may be more prone to having very poor braking. Your mechanic is wrong that there is nothing that can be done to improve your cable disc brakes, but there would still be some expense involved.

The cable routing may be implicated. It's possible the bike is designed with too tight bends. If this is the case, I'm not sure that this would be fixable.

After you do what Criggie recommended, compressionless cable housing is frequently recommended for cable disc bikes. The downside is that this is expensive, and requires a fair bit of labor to redo the bike. It's possible that if the manufacturer cheaped out on the stock housing, that might cause problems - if it's too flexy, that robs your braking power. If you need to ditch the stock housing, then I think you might as well spring for good housing.

I'm not familiar with disc pads on cheaper brakes, but it's possible that changing to a high quality pad would help. We do see this phenomenon on rim brake bikes. If you do this, you will need to sand off the rotor surface and break in the brakes - as an aside, if you weren't aware that disc brakes need breaking in, and if the store didn't do this (or you bought consumer direct), then this is something to be aware of. Anyway, pads are fairly easy to replace if it should come to this.

On bikes in the US$1,500 range, I think it's possible to spec lower end hydraulic brakes (e.g. Shimano Tiagra), and even low end hydraulic brakes work well. On bikes in the sub-$1,000 range, I do wonder if it would be better to spec rim brakes, due to the possible issues with cable disc brakes. Again, what you describe is not guaranteed to happen, but cable disc brakes may take more careful speccing to make them work.

Answer 4

I'm sorry you've had these problems, but I'd suggest part of the problem is with the mechanic. I've had two cable disc-braked bikes now and, while repairing and adjusting their brakes is certainly different to rim-braked bikes, it's definitely possible without having the issues you're describing here - though did, many years ago, prove beyond my old mechanic. To be honest I've had more problems with my hydraulic-braked bike, and rim brake adjustment was always the job I enjoyed least; I wouldn't say discs are necessarily harder, just different. And once set up properly, I've always found their performance stronger and easier to use than the rim brakes I'd ridden for 20+ years before (and still do on my folder).

More experienced mechanics than me have given detailed advice which makes sense to me. I'd suggest trying what they're suggesting, and hopefully you'll have an enjoyable, rideable bike very soon.