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[Closed] strange brake issue
On the rear of the tandem
Its got old hope six pots front and rear. The front is a great brake but the rear is not.
I thought it might be contamination from the rohloff which does tend to leak a little oil mist that side so I changed both pads and disc and made sure all pistons in the caliper are moving freely and its centered as per the hope method.
It just does not produce enough friction. We have been away touring with some heavy loads and I tried dragging it down hills - it got very hot but remained ineffective. At one point it started to feel like it was working properly but it never did - getting worse thru the tour
It feels to me like glazed pads. But glazed from brand new and if it was would getting very hot not break the glazing down?
Any ideas - I really like them on the tandem because they cope with heat well but I need a working rear brake
Did you try sanding and cleaning the rotor?
brand new rotor. I did try putting peaty mud all over it while we were away to act as an abrasive but I didn't sand it before installation.
My guesses would be that your hub is still spraying oil on the rotor or the surface of the new rotor was contaminated.
no sign of either thanks tho
Same pads and rotor as the front?
The brand new rotor may have had a protective oil on it and contaminated your existing pads, or perhaps you are using sintered pads which have glazed over and are not transferring a braking residue onto the rotor, give the rotor a clean using IPA and try a set of organic pads, bed them in by doing 10 hard braking runs down a hill/slope by braking progressively harder as you complete the runs. This will transfer braking pad residue onto the disc which is essential for consistent braking.
Or...if the discs are the same size front/rear (unlikely i know) then swap round pads/discs to see if that helps
I do use sintered pads.
Could be a slight leak on a caliper seal?
Put the front rotor and pads onto the rear. See what that does?
rotors are differnt sizes or I would try that.
I had the brake hot enough to blue the disc and sizzle when I put water on it - surely that would have burnt off any contamination?
It feels to me like glazed pads.
Are they glazed? No point in guessing when it's easy to have a look and answer the question right away.
surely that would have burnt off any contamination?
Doubt it would burn off brake fluid, for obvious reasons
Has it always been poor? Must be producing friction otherwise it wouldn't get hot...
The only thing I could suggest is that if you are using aftermarket pads, try going back to Hope. I've recently started using original Shimano and surprised at how long they are lasting, I'm sure they've done four times the miles and they are far from worn yet, so wondering if superstar etc are a false economy now.
Might be worth switching to a modern setup with finned pads otherwise.
The sintered pads may have baked/overheated (easy to do on a tandem when dragging/feathering rear brake) and glazed/baked the surface/compound to such an extent that transference of pad material is impossible to attain, very well could be what has happened if you managed to blue the disc, for the sake of £10 id be tempted to try a softer organic compound such as EBC green and bed them in gradually (once the disc has been cleaned/given a light sand with emery paper.
What does the lever feel like when you are braking hard, I can easily lock the rear wheel of my tandem which has cable operated BB7s, could your rear brake need bled or have a leaky seal as others suggested?
I've blued the brakes on my tandem before and they have always been fine once they cooled down again, apart from the one time with the factory fit organic pads that got so hot they disintegrated, sintered pads fixed that though.
Well I stripped it down and the pad surface is greasy so contaminated they are. I thought I had cured the rohloff leaks but maybe not. No evidence of oil anywhere tho.
Ho hum. Thanks for your help
I have a spare caliper so will try that