Cable disc brake clicking when brake lever is pulled the full way back

[slowster]

I think it may be over camming, as described in these two posts:

viewtopic.php?p=664618#p664618

viewtopic.php?p=626367#p626367

I haven't found any information on how the things actually work?

It has never happened to me and I don't have the experience of having dismantled a caliper. From the descriptions I have read I take it that with some designs of caliper there is a point at which the ball bearings on the ramp which push the piston, reach the design limit of their movement/range, and any further movement as a result of excessive cable pull/overly worn pads will result in a *loss* of pressure/force against the piston, and the piston springing back.

[mattsccm]

Tekro Lyras were prone to over cam. Once the pads were well worn you could squeeze harder and harder to compensate and they suddenly lost all power. Backing off brought them back to the merely inefficient state. A mate had the same thing with some cheap and nasty Promax brakes. These are often fitted to cheaper bikes and work passibly when new but are soon about as effective as putting oe of your daps on the back wheel. Easy to fix though. Chuck them away and fit some BB7s or the dual pull TRPs

[zenitb]

this sounds horrible and dangerous !!!

Just so we can get more information on the issue is there a pad adjusting screw on the OTHER side of the brake to that shown on the video ?

Something like this? pad adjuster.JPG

If there is, is it tight or slack ? And does tightening it change the symptoms ?

Hi zenit.

I have had a little play around just now with the screw - it wasn't exactly loose to start with but not tight enough to feel resistance - and having tightened it a little the noise has completely gone and the lever doesn't travel nearly as far back, but there is some slight interference.

Ok so when you spin the wheel now you get a little sound each revolution indicating the disc is lightly grazing the pad now ?

If so there are a couple of options:
a) the disc is very slightly bent? Maybe watch the edge of the disc to see if it moves in and out a bit
b) the disc brake mount itself is slightly out with regard to the disc on the wheel ? This can be adjusted with the two allen key bolts holding the brake on the forks. This is safety critical though. Might be worth just popping back into Decathlon to get them to do it, at least for the first time. It sometimes takes some twidding to get just right.

If you do take the bike in get them to check pad wear. The fact you had to adjust the pad adjusting screw makes it sound like the pads have worn a bit.

Let us know how you get on.. everyone on here is keen to help out..

[offroader]

I think it may be over camming, as described in these two posts:

viewtopic.php?p=664618#p664618

viewtopic.php?p=626367#p626367

I haven't found any information on how the things actually work?

It's quite a simple system common on cable operated motorcycle clutches. My 1970s Honda had the exact same system to operate the clutch pushrod so it's certainly not something Avid invented

The actuator arm is attached to a disc with a number of ramps on it. As the actuator arm moves the disc rotates and the ramps move along.
The moving piston has a corresponding number of ball bearings sitting in dimples. The piston is not round so is held at a fixed angle in the caliper body where the balls sit at the bottom of the ramps on the actuator disc in the rest position.
When the actuator is rotated the balls effectively climb up the ramps as the piston doesn't rotate. This pushes the piston and actuator apart giving you the piston action


Note. The Avid BB calipers use the same principle but work slightly different. The balls sit in dimples machined into the caliper body. The actuator arm is directly attached to the piston which has ramps machined on the back. Operation is the same but you'll see that the actuator arm moves in and out in the caliper body as it rotates

Over camming happened in bad designs when the actuator can rotate far enough for the balls to fall off the end of the ramps

[Cyckelgalen]

As someone suggested chucking these brakes away and replacing them with TRP Spyres, I have to add that I have seen a set of TRPs doing exactly the same thing. It wasn't my bike, and never had a chance to look closer into it or try to sort it out.
I did take apart a different set of Spyres and they work as just like that, three balls that roll along ramps and move the piston out as the actuator arm rotates.

I also believe it's an adjustment issue, I would try new pads, or at least not as worn as the current ones, and tweaking with travel, cable length etc.

[TheBomber]

I may have missed it, but it doesn't look like anyone has linked to the user setup manual yet:

https://s3.us-east-1.amazonaws.com/prom ... _V1_EN.pdf

As the consensus seems to be 'over camming' then the last paragraphs under 'Ongoing maintenance' look to be the most relevant. If the inboard pad has never been tightened then that would surely lead to the over camming and limited remaining movement for actuator arm problems. Given the seriousness of the problem I'd be getting the pads out to check them, and then going through the whole alignment and cable setup procedure.

[hoogerbooger]

Does sound like over-camming.... as Colin and others have advised.

I've had this on TRP Spyres before I realised you should use the pad adjusters to allow for pad wear rather than using the barrel adjuster and/or adjusting brake cable. Need to make sure actuator arm does not travel too far.

It's a very alarming noise, although I think yours is louder than I had on the Spyres. When watched closely, it was very obvious that one pad jumped back away from the disc when it went PING. Since using the pad adjusters ... and being mindful of brake actuator arm travel/ position when setting up/ adjusting....no more pings and brakes fine.

Good luck with sorting it.

[531colin]

Note. The Avid BB calipers use the same principle but work slightly different. The balls sit in dimples machined into the caliper body. The actuator arm is directly attached to the piston which has ramps machined on the back. Operation is the same but you'll see that the actuator arm moves in and out in the caliper body as it rotates

Over camming happened in bad designs when the actuator can rotate far enough for the balls to fall off the end of the ramps

Ah! I have only ever used BB7s, and therefore only ever stripped BB7s

....I couldn't see how they could "go over" because there isn't an "end" of the ramps for the balls to fall off.! Thanks for the explanation!

[doffcocker]

As always many thanks for your responses.

Just an update on this.
A few weeks ago I took the bike into Decathlon as they do a free 3month safety check on all new bikes.
The guy adjusted the brakes for me and the lever worked with much less pull back distance.
I told him about the noise and he was unconcerned, he said he checked for brake pad wear and he said they were nowhere near worn, he even said they should last another few months at least.
Then this week I decided to tighten them up again myself at the cable and clamp as the lever travel distance had gradually increased again since taking it into the shop.
This seemed to work fine and the brakes themselves are working fine, it's just there is still that clicking noise, albeit much quieter than previously when applying a lot of force on the lever.
I know a great deal of this is paranoia induced, I just have been feeling generally more anxious on the roads lately and quite kean to get some peace of mind at least as far as the brakes are concerned.

[aflook]

[quote=hoogerbooger post_id=1747328 time=1672766282 user_id=11046

I've had this on TRP Spyres before I realised you should use the pad adjusters to allow for pad wear rather than using the barrel adjuster and/or adjusting brake cable. Need to make sure actuator arm does not travel too far.
[/quote]

I think this is important: adjusting pad clearance with the cable could lead to complete brake failure because it limits the function of the actuator.

[doffcocker]

Update on this.
I had to do some adjustments today as although I haven't heard the noise for a while, the lever is starting to reach further and further back so I wanted to tighten this up.

Anyway I can't seem to tune them so that there's enough braking power and no brake interference.

I have removed the pads (pictures attached), I have no idea what I'm looking for in terms of signs of waring.

But in the midst of trying to tune the brakes by adjusting both the screw and cable, I come across not only the loud noise again but most alarmingly what it sometimes coincides with. As you can see the wheel brakes, then fails with the hand still firmly pulling the lever, and the wheel continues to run free. (Video to follow)

[doffcocker]

https://photos.app.goo.gl/ApHdJrMkK2cms5ea8

Video shows the brake slowing down the wheel before failing.

[rareposter]

I suspect that what you're about to get now is a host of suggestions as to what is wrong and supposed solutions to the alleged problem but I would suggest that far and away the best thing you can do at this stage is take the bike to a reputable local shop and get them to have a look at it.

You're onto safety critical parts combined with (from your other thread about holding the levers) a feeling of being unsafe anyway which is a really really bad combination that's not going to be solved by people posting suggestions on here (no matter how helpful they intend to be).

It's very difficult diagnosing fit and mechanical issues via pics and short videos.
If you post up an approximate location of where you are, folk on here may be able to recommend decent local shops with good mechanic support.

[wirral_cyclist]

One pad worn out, half of it worn semi diagonally and you can see rivets too. How many miles on it, where do you live (roughly) as it's either hilly or you ride with the brakes on. As you aren't any good at maintenance just take it to a bike shop, again give a rough location and someone might be able to recommend a bike shop, hat might also check your bike fit (other thread).

[531colin]

You have worn right through the friction material, now you are grinding away at the metal backing, and also of course the disc.

I'm a very late adopter of disc brakes, but I believe the friction material is bonded onto the backing (not riveted) and you are recommended to fit new pads while enough friction material remains to stop the heat from braking melting the bond.

i imagine the brake is coming to the end of its travel (over-camming, as before) and releasing the disc