3

A few days ago my rear (disc, hydraulic) brake started feeling a bit funny, then “went” completely. I took it to the shop where it’d just been serviced a week earlier and they said I must’ve got a rock or something in between the callipers and the disc, because one pad had been totally ripped off. They replaced the rear pads.

When I went to take it back I immediately noticed that the “travel” on the rear brake lever was much longer than the front, and it was also somewhat “squishy”—previously when pulling on the lever there was a “hard stop” at the end where the pads would bite on the disc with a relatively light touch on the lever and the wheel was going nowhere.

I pointed this out and the mechanic tried to fob me off saying something about the rear brake’s line being longer so they’d never feel exactly the same something something. But this is entirely bullshit because they were both precisely the same travel and “sharp” feel two weeks previously, and had been after every service the bike’s had, including pad changes. I took it back again yesterday, had a shouting match with the original mechanic, then waited for another one who took the bike back and said they’d try bleeding them again.

Is balancing the feel of hydraulic brakes like this unreasonably difficult or are they just rushing the job or being lazy?


More info: Brakes are Magura brand, and until now they've been pretty much perfectly evenly matched.

9
  • 1
    Check the hydraulic line for damage like a hard bend or a line where a hard bend might have been. Dec 2, 2021 at 8:27
  • 1
    A botched job while bleeding the brake and maybe a failure to inspect the calliper for further damages (piston?) other than the ripped off pad.
    – Carel
    Dec 2, 2021 at 8:37
  • 1
    I think this is why the mechanic was so mad at me for calling her on it being not quite right—because they buggered up the service somehow which led to the brake failing a week later. But I have no proof of that so I have to give them the benefit of the doubt. Dec 2, 2021 at 8:40
  • Also, what kind of brake? You might be a victim of “Terminally Squishy Deore Syndrome” Dec 2, 2021 at 11:45
  • @WarrenBurton - not just a Shimano issue, any hydraulic brake feels squishy after you do anything to it once out of the box! Brake bleeding is a black art like wheel building, you're better off going to witch doctor than any old LBS.
    – DWGKNZ
    Dec 2, 2021 at 12:41

3 Answers 3

7

The things your story leaves unclear: if the rear didn't have any bleed type symptoms when you first brought it, why did it get bled at any point? Bleeding doesn't usually happen preventitively in shops and also not as part of a pad replacement. Unless they did it preventitively as part of some kind of service package and then did a bad job of it, it's curious what happened to the brake that made it need it in the first place. It's also curious what happened to make it lose the pad, which is highly unusual. It is possible to make the mistake of not getting a pad retaining pin properly through a brake pad, and that's one way of losing them, and it's also possible for the pad material to come separate from the backplate, but that's rare. (I have seen it once on a new Covid-era brake pad on a new bike, of hundreds I see a year, and never before the past year). So all told, it's really unclear what happened to this brake and why. It's possible that what happened is when the pad came off, the piston behind it got overextended to the point of leaking fluid or coming out completely, which would then require a bleed. That chain of events makes sense but the extreme weirdness of losing a pad like that still makes it feel like there could be something more going on.

As to the question, the answer is that when the quality of the bleed is good on both brakes and there's still a mismatch in feel and/or travel, the options are limited and mostly involve going a lot more in-depth to even try.

For travel aka bite point, first note that almost all hydro levers have reach adjust, but that's not relevant because it has little or no bearing on bite point, just reach, and any effect it does have on bite point isn't relevant because if you use it that way you're making the starting reach of the brakes asymmetrical. Some levers do have bite point adjustment that's independent of the reach adjust, which in some situations can be used to make lever feel more symmetrical, but even then usually only when something is wrong with one of the brakes that's bringing its bite point artificially far out, like over-extended pads that result from sticky pistons. So making the bite point adjustment asymmetrical can be a piece of the puzzle in tuning feel when you have bite point adjustment, but mostly only when something else is wrong.

Other than the above, there is basically no tuning bite point. It tends to be at its furthest out with new pads, although how much difference that makes depends on the specific brake and whether it's an open or closed system etc. Sometimes people mess around with intentionally overextending the pistons during a bleed (intentional fluid overfill) to get a shorter bite point, but most of the time that's a bad idea because it makes the pad gap less than it should be. It's anything but a normal thing to do.

For feel, it is true that all rear brakes feel squishier than their matching fronts even when things are perfect. What makes a brake feel firm is no air, no compression of the fluid, and no flexing of the hose. No fluid or hose is perfect, and rears have more of both, hence more squishy feel. It is a relatively minor effect but it's always there, unless maybe you do something drastic and weird like mismatch hose types. This effect is princess-and-the-pea level, and tiny compared to soft feel that results from air contamination in the line, which makes the brake feel like mush.

There is no using the bleed procedure to tune the feel, other than the aforementioned intentional fluid overfill hacks, which can be done by using a shaved bleed block etc. Bleeding takes all the air out and is successful when it does that and unsuccessful if not.

Piston stickiness can cause pad retraction issues that reduce the pad gap and also reduce lever stroke, but not feel mushy. Those issues are not always possible or cost-effective to fix; it's pretty common for a new caliper to be the only practical way, and so they are responsible for shops doing everything possible in some situations and still handing back a bike with significantly asymmetrical brake feel, but neither brakes should still be mushy. There are a lot of brakes where it's common to have some level of this even though the brake is still functional - many Avid/SRAM models are like that.

2
  • Amazing, great write-up, thanks. So given the amount of difference between the left and right levers, my current suspicion is that it was a bad bleed job, and if they can't fix it then something more fundamental in the brake itself must have been busted either while it was being serviced or in the process of the pad coming off. Dec 3, 2021 at 12:39
  • 1
    That's a reasonable guess but for me personally it's hard to get away from the weirdness of the pad coming off in the first place and how that might fit into the story. Also knowing it's a Magura now: Magura is not difficult to bleed but they have their own quirks and are a little less common, so maybe that has something to do with it. It's also possible that what happened is the piston got overextended and lost fluid, but then the shop pushed it back in and wiped it without bleeding the brake at all. That would explain what happened too, but again not how the pad was lost to start with. Dec 3, 2021 at 18:02
3

It's reasonable to expect a hydraulic brake to feel brand new after being serviced by a "professional". In my personal experience, an LBS should have the skills and experience to bleed a brake to feel factory new.

Without knowing your actual brake set, however, it's hard to tell if this is a poor bleed job or a poor set-up issue though. Squishiness generally comes from air in the lines / not enough fluid but can be caused by other things.

However, because a second mechanic at the LBS was willing to redo the work, then possibly the first mechanic is new or still in training. It may not be laziness or a rushing issue, it just could be a lack of experience. They've offered to try to rectify the problem (albeit after a yelling match) so I'd let them.

Also worth bearing in mind, lever travel can (mostly) be adjusted by the screw/ knob on the lever. Have you tried to wind this in to shorten the pull? This may help what you're feeling.

1
  • It's definitely not (just) an issue with the travel on the lever. Dec 3, 2021 at 12:41
0

I'm no expert with hydraulic brakes, but I was able to bleed a brake successfully given a couple of slow attempts. Someone who does it frequently should be much faster and get it first time.

However you say the caliper had suffered physical damage enough to tear an entire pad clean out. That kind of force is sufficient to bend and distort things, including the caliper, the pad-retention bolt/wire/spring, and maybe even the frame mounts and bolts.

It would have been reasonable to inspect the mounts and caliper, and to consider replacing the caliper if it was at all distorted or the pistons were damaged. If the frame mounts were tweaked, they may need machining/filing back to flat and level.

If anything was distorted, then dialling in the pad fit can be hard, so you have to leave things a little wider than normal, which could result in a long travel, minimal bite, and general poor braking.


Upshot, if you're not happy with that bike shop then find another. Or you can learn to do these things yourself with some mechanical aptitude, sufficient time here on SE/youtube, and no pressure to get it ready quickly.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.