Front disc brake not working.

[trogg]

Hi, my daughter is having a problem with the front disc brake on her electric bike, when she pulls the leaver it starts to brake but then suddenly there is a click coming from the front disc and the leaver closes to the bar and she is left with no brakes.
Bike is less than 12 months old and she bought it under the cycle to work scheme, because of this I haven't tried to take it apart yet but I'd still like to know what it could be.
Did do a little video but I can't load it these forums.
Thanks.

Edit to add, brakes are cable operated and the problem is definitely inside the brake caliper.

Edit to add video link https://youtu.be/UFLtLRiR6iw?si=_8Gsrv_bjnP5fwYs

[AndyK]

Is it a hydraulic or cable-operated brake? (From your biker avatar I'm guessing you know what a hydraulic brake looks like. )
Any visible damage to the cable/hose between the brake and the lever?
Normally for videos people stick it on YouTube or somewhere then link to it. If you can't provide the video then some photos would help, including a close-up of the brake calliper.
If it's less than a year old this sounds like something the shop should be sorting out under warranty.

[DevonDamo]

Without photos/video, it's a guessing game, but my guess (assuming it's a hydraulic system) would be that there's a fault with the lever mechanism. It's a simple mechanical system whereby the lever pressure is translated (via a pivot) into a short, hard push on the master cylinder. This can have any number of linkages and actuator rods, often held in place with little bits of plastic - one of which I reckon has broken. I had a similar problem on one of my bikes, and the only solution was to replace the entire lever assembly - I couldn't find spare parts. If this is the case, then regardless of whether you can diagnose the problem or not, you're still going to need to get the bike provider to swap out this part.

[trogg]

Is it a hydraulic or cable-operated brake? (From your biker avatar I'm guessing you know what a hydraulic brake looks like. )
Any visible damage to the cable/hose between the brake and the lever?
Normally for videos people stick it on YouTube or somewhere then link to it. If you can't provide the video then some photos would help, including a close-up of the brake calliper.
If it's less than a year old this sounds like something the shop should be sorting out under warranty.

Thanks I've just edited my original post and I'll get a video uploaded onto YouTube as soon as I can, cheers.

[trogg]

Without photos/video, it's a guessing game, but my guess (assuming it's a hydraulic system) would be that there's a fault with the lever mechanism. It's a simple mechanical system whereby the lever pressure is translated (via a pivot) into a short, hard push on the master cylinder. This can have any number of linkages and actuator rods, often held in place with little bits of plastic - one of which I reckon has broken. I had a similar problem on one of my bikes, and the only solution was to replace the entire lever assembly - I couldn't find spare parts. If this is the case, then regardless of whether you can diagnose the problem or not, you're still going to need to get the bike provider to swap out this part.

Thanks, I've just edited my original post, it's cable.

[Brucey]

some mechanical (cable operated) disc brakes are notorious for doing exactly this; all such brakes use an actuator that comprises three balls on three ramps, which is fine provided you don't run out of ramp. If you do, the result is usually that the brakes start to come on, before you get the click/no brakes thing. A whole load of tektro brakes manifested this behaviour, and were consequently recalled.
However, even in bad brakes, this only happens when the pads/disc are badly worn. E-bikes can be pretty hard on brakes, and pads don't last long anyway, so......

[trogg]

some mechanical (cable operated) disc brakes are notorious for doing exactly this; all such brakes use an actuator that comprises three balls on three ramps, which is fine provided you don't run out of ramp. If you do, the result is usually that the brakes start to come on, before you get the click/no brakes thing. A whole load of tektro brakes manifested this behaviour, and were consequently recalled.
However, even in bad brakes, this only happens when the pads/disc are badly worn. E-bikes can be pretty hard on brakes, and pads don't last long anyway, so......

Thanks Brucey, to me it looks like there is plenty of meat on the pads, however it must be worth putting new ones on and giving it a try.
I know on my mates bike he wore the pads go right down to the metal, and even then they still worked to a degree.

[531colin]

With cable disc brakes you must take up pad wear using the pad adjusters.
If you only adjust using the cable barrel adjuster you will run out of the slope the tiny ball bearings run up, as Brucey says

[Cyclothesist]

I agree with 531colin. The caliper lever arm looks to be operating very close to the barrel adjuster with only a short cable throw. The pads do not look worn out. As Colin says if you haven't used the pad adjuster screws to move the pads towards the rotor as they wear, and instead shortened the cable it results in the lever arm being at the end of its stroke on braking.
It's concerning that this brake caliper will pop the ball bearings off the end of the ramp towards the limit of the brake arm range. Its not exactly a fail safe design. Some early Spyre brakes were recalled because of this issue. The brakes pictured are single mechanical piston type so definitely not Spyres. They may be faulty or just a bad design. Personally I'd take the bike back to the retailer for assessment. If it's a bad design I'd replace it, and the back one too with something more robust and reliable.

[trogg]

With cable disc brakes you must take up pad wear using the pad adjusters.
If you only adjust using the cable barrel adjuster you will run out of the slope the tiny ball bearings run up, as Brucey says

I agree with 531colin. The caliper lever arm looks to be operating very close to the barrel adjuster with only a short cable throw. The pads do not look worn out. As Colin says if you haven't used the pad adjuster screws to move the pads towards the rotor as they wear, and instead shortened the cable it results in the lever arm being at the end of its stroke on braking.
It's concerning that this brake caliper will pop the ball bearings off the end of the ramp towards the limit of the brake arm range. Its not exactly a fail safe design. Some early Spyre brakes were recalled because of this issue. The brakes pictured are single mechanical piston type so definitely not Spyres. They may be faulty or just a bad design. Personally I'd take the bike back to the retailer for assessment. If it's a bad design I'd replace it, and the back one too with something more robust and reliable.

Thanks both, you learn something new every day lol, I'll take a look again tomorrow and let you know how I get on.

[trogg]

Thank you everyone for your replies,
bike up and running now, I loosened off the cable, centralised the calliper and screwed the pad towards the disc.
There is a slight warp in the disc but I'm not worried about that for now, the brakes work great.

[Brucey]

FWIW I agree too. In fact, some calipers are exclusively fitted with pad adjusters and there is no barrel adjuster on the caliper at all.