Disc brakes for dummies?

[swee'pea99]

My wife recently bought a b'twin electric bike and loves it, but she reports that her front brake has stopped working properly. I've recently replaced the cable, and I know it's fine. The mech seems to be working fine, and if you use the brake while spinning the wheel in the air, it stops immediately. But if you push the bike on level ground with brake fully engaged, it slows the wheel slightly, but not much, and it's not hard to push through.

I really don't know where to start - I've only ever worked on caliper brakes. If it helps, it looks like this:

Worn pads? I guess would be the obvious place to start. But maybe I'm wrong. If it probably is pads, are they easy to change? Is it intuitive? Are there tiny little springs that will leap across the kitchen the moment I loosen a screw? Do I need to get Tektro pads, or are disc brake pads standard sizes? Or might it be something else entirely? And all points north.

Any hints & tips much appreciated.

 

[T4tomo]

a good place to start is to google for video on adjusting / setting up cable operated disc brakes or the manual for your model of tektro brake.

in short you have too much gap between pads and rotor and need to dial in the pads a bit to compensate for wear, much like you would be tweaking the fine adjustment barrel on a caliper brake.

is this the fine adjuster on that model? looks like it (sometimes they are nearer the pad, hence the gumph written above before I spotted that)

edit to add, also if once tightened it rub on one side, you may need to re-centre it. again videos abound on you tube, but slacken off the allen bolts to the mount so the caliper unit moves. pull the brake on tight, and holding the brake on , retighten the allen bolts. release brake and the rubbing should have gone.

 

[fossyant]

Contaminated discs/pads ? Got oil anywhere near them ?

 

[swee'pea99]

a good place to start is to google for video on adjusting / setting up cable operated disc brakes or the manual for your model of tektro brake.

in short you have too much gap between pads and rotor and need to dial in the pads a bit to compensate for wear, much like you would be tweaking the fine adjustment barrel on a caliper brake.

is this the fine adjuster on that model? looks like it (sometimes they are nearer the pad, hence the gumph written above before I spotted that)
View attachment 665220

edit to add, also if once tightened it rub on one side, you may need to re-centre it. again videos abound on you tube, but slacken off the allen bolts to the mount so the caliper unit moves. pull the brake on tight, and holding the brake on , retighten the allen bolts. release brake and the rubbing should have gone.

View attachment 665222

Brilliant, thanks. Just tried adjusting the screw and I think it's worked and it feels like it's made a big improvement. I'll await feedback, but so far so good. Cheers.

 

[swee'pea99]

Contaminated discs/pads ? Got oil anywhere near them ?

Oh, and - nope, don't think so. All looks very clean and tidy (tho' I've taken the precaution of giving the discs a once-over with isopropyl alcohol, just for the craic).

 

[T4tomo]

You can take all the credit and tell the mrs she's cooking you tea as a reward....

 

[I like Skol]

In general with cable discs you DO NOT ADJUST via the cable adjuster once that is set up correctly. The arm has limited movement and you want to keep that in the sweet spot once a cable is fitted.
The correct way to adjust for pad wear is to wind in the pads a bit, which depending on model can be easy or not. Brakes with adjusters on each pad are easy, just screw in each pad until almost touching disc and you have a firm lever with no excess travel.
Your brake seems to be one of the simpler units with a fixed pad and an adjustable pad at the rear side. This is a bit more tricky but still simple. You need to move the fixed pad as close as you can to the disc. Easiest way is probably to release the mounting bolts and squeeze the brake then tighten bolts before releasing. Now adjust other pad which should be even further away from disc after you moved the caliper to align the fixed pad.
It may take a couple of goes to get the ideal alignment with enough clearance to avoid any scraping/rubbing. Discs are rarely completely straight so it is sometimes a balance or compromise between immediate bite or no rubbing.

As Fossy has said, it might not be wear/adjustment at all and might just be contaminated pads/discs.

 

[I like Skol]

I'll just repeat for clarity, DO NOT ADJUST THE CABLE BARREL, unless there is excessive lever travel before the caliper arm starts to move.

 

[Jody]

As Fossy has said, it might not be wear/adjustment at all and might just be contaminated pads/discs.

Certainly looks to have some build up on the caliper and where the pad sits

 

[swee'pea99]

Hmmm. Ok, well, like I say, I've done it and it seems to have done the trick, so I'll see how it goes with 'er indores and then start exploring further if necessary. And thanks very much for the detailed 'how', whether it comes to that now or (as seems certain) at some point.

 

[T4tomo]

I'll just repeat for clarity, DO NOT ADJUST THE CABLE BARREL, unless there is excessive lever travel before the caliper arm starts to move.

The barrel adjuster does the non-fixed pad, there should an allen key adjuster for the round the back of the caliper for the fixed pad. You may need to adjust both to compensate for wear.

the fact that a tweak of the barrel has helped, suggest it did need doing, the OP should also check the fixed pad isnt to far away from the rotor and adjust if necessary. generally wind in until it just catches and then back it off slightly until it doesn't!!

https://www.trpbrakes.com/userfiles/file/Tektro MTB/Aquila Manual.pdf

 

[si_c]

I'll just repeat for clarity, DO NOT ADJUST THE CABLE BARREL, unless there is excessive lever travel before the caliper arm starts to move.

For a higher end cable brake I'd agree with you, but that looks like the MD-M280 brake, which doesn't have a floating pad adjustment, there should be a pad adjustment for the fixed pad, but the actuated pad is adjusted by the barrel adjuster. That being said it is important to change both pads, wind in the fixed pad until you hear it making a noise then back it off until quiet. Then use the barrel adjuster to change the floating pad position, ideally so that the brakes work functionally but that there is still a good amount of lever travel.

Those brakes will work fine, but you will need to keep on top of making sure the pads are in a good position as they wear. If you wanted to upgrade them, then you could get something like the TRP Spyres (also made by Tektro, but their premium brand) which have quick pad adjustment for wear without adjusting cable length as @I like Skol says above, but to be honest if you're upgrading the brakes then a set of Shimano Hydraulics is the obvious upgrade, I got a pair of MT200 brakes for under £50 as a sealed kit with hoses all ready to go.

 

[swee'pea99]

The barrel adjuster does the non-fixed pad, there should an allen key adjuster for the round the back of the caliper for the fixed pad. You may need to adjust both to compensate for wear.

the fact that a tweak of the barrel has helped, suggest it did need doing, the OP should also check the fixed pad isnt to far away from the rotor and adjust if necessary. generally wind in until it just catches and then back it off slightly until it doesn't!!

https://www.trpbrakes.com/userfiles/file/Tektro MTB/Aquila Manual.pdf

Thanks, I've tightened that a bit too. Now to wait for the test ride!