Brake failure

SwampRodent

Pedelecer
Jun 19, 2019
34
9
Hey peoples,

Does anyone else suffer repeated rear brake failure on their ebikes (or any other bikes)?

I commute into Sheffield every day which means I have some pretty savage hills to play with. I can usualy get 4 - 6 weeks out of a set of brake pads (Shimano Zee 4 piston calipers front and rear) less if there has been a wet period, however every few months the rear pads just give up the ghost, they look perfectly OK but loose 100% of the friction, I can squeeze the lever to the point of breaking it or blowing a hose and nothing, zilch, nadda just an unbelievable ear shredding noise like an old bus coming to a halt with every dog in a 2 mile radius barking and howling.

Admittedly I am very heavy on the brakes either coming to a halt from 30 mph+ at the bottom of a steep hill or braking every few seconds as I speed through some of the hilly suburb's. I always use both front and rear brakes at the same time to keep the bike balanced often feathering the rear to keep the bike strait if I'm doing an emergency stop (car cutting me up ect). I have a muddy 60% / 30 degree climb / decent (flood embankment) which takes a bit of finesse on the brakes!

I'm currently using Uber orange Kevlar pads that give a good feel, are not to hard on the rotors and if I buy them in bulk cost about £6 a pair, other pads fail in the same way.

I'm kind of at a loss as to whether they are glazing or getting contaminated. Sometimes such as this morning if I repeatedly pump the lever to get some heat into them they start to work to a degree, other times it makes no difference. I don't think its the hydraulics as if I put new pads in the system works perfectly. I have taken the failed pads out and sanded the top layer off and washed the rotors in acetone but still no friction and lots of squealing. If its oil contamination which I suspect it is then I am at a complete loss to where it is coming from, I do ride across country so there is a lot of dust, nettles, weeds ect. Also I ride in heavy rush our traffic so maybe its some sort of airborne contamination.

When I first started ebiking I was using rim brakes but these never ever worked as every time it rained it would wash chain oil onto the rim, currently I oil the chain very sparingly and keep a good lookout for anything on the rear wheel. The front brakes never have this problem but the pads will wear away in a few days if the rears stop working.

I've yet to turn the rotors blue but have burnt myself when I've stupidly torched them after I reach my destination!

In an ideal world I would just love regen braking to offset the pads.

Any ideas?
 

SwampRodent

Pedelecer
Jun 19, 2019
34
9
Thanks Fishy, they are pretty much what I'm using now together with 203mm rotors, these brakes are absolutely awesome with very good modulation. The model in your picture has heatsink fins on the pads.
I think the difference between the Zee and saint is with the lever assembly.
 

SwampRodent

Pedelecer
Jun 19, 2019
34
9
OK, this is going from weird to bizarre!

Yesterday my front brakes decided to leave the party,( I've kind of got used to getting only two or three days out of the rear pads). The night before the front brakes were perfect then yesterday morning they barely worked, we are talking 203mm discs, 4 pot callipers and sintered pads, at 20 mph if I grabbed the lever full on the bike would slow to a halt like a 1920's rod braked boneshaker but with the sound of a dozen people scratching their finger nails down a blackboard...erm...chalkboard at the point of the wheels coming to a halt.

On one of the steep descents into work I braked as hard as I could from 25 - 30 mph down to standstill several times to get some heat into the discs to try and burn anything off, they improved somewhat but had a bit of a 'rubbery' feel to them. I noticed the day before that after the rears failed they would work in the rain so I let the discs cool for a few hundred yards then squirted some of my drinking water on them and try again...they were suddenly back to 100% and I locked up the front wheel!!!???

This morning it was raining so I had both front and rear brakes which is a bit of a novelty, tonight its supposed to be dry so I will see what happens.

Its almost as if something does the opposite of bedding the pads in, what ever it is it usually happens at the weekend when the bike is not being used.
 

soundwave

Esteemed Pedelecer
May 23, 2015
15,971
6,292
you need some decent rotors as the heat will be killing the pads.
DSC_0290.JPG
that was destroyed in one day at the forest of dean not had a problem since using 203mm hope rotors not cheap but does the job with sinterd pads
 

SwampRodent

Pedelecer
Jun 19, 2019
34
9
That's actually an interesting point, the last leg of my homeward commute is down a steep hill into the village, I have to turn right at the bottom of the hill so have to be doing traffic speed (30mph + ) to get over to the centre of the road then hammer the brakes at the bottom for a mini roundabout, I know when I get off the bike at home I felt the front rotor once and burnt my finger ( yeah OK I know....). The strange thing is that its generally always the rear pads that fail.

Just to be clear, I don't have a 30mph e-bike I just live somewhere VERY hilly :)
 

flecc

Member
Oct 25, 2006
52,763
30,349
I know when I get off the bike at home I felt the front rotor once and burnt my finger ( yeah OK I know....). The strange thing is that its generally always the rear pads that fail.
The rear will probably have rather less cooling air passing over it than the front disc. Also the upward spray of water from the front tyre tread with road contaminants like diesel oil and particulates, plus rubber plasticizers from tyres will be going onto the rear disc to some extent.
.
 

soundwave

Esteemed Pedelecer
May 23, 2015
15,971
6,292
that rotor was of the rear stock rotors are crap as my bike can do 30mph on the flat and they just cant cope with the heat buildup and nukes the pads.

these are what i use now
DSC_0063_01.JPG
 

SwampRodent

Pedelecer
Jun 19, 2019
34
9
Hey all, I figured I would give an update on this to help anyone else with a similar issue.

Basicaly new pads fitted in the rear callipers would fail after only a day or twos use leaving no useable braking efficiency, then the front brakes also started to repeatedly fail. After a continued dry spell, i.e. the bike was not still soaking wet from rain at weekend when I service it the cause became evident.

It was kind of obvious really but as the hydraulic callipers are the thick end of £70 each I probably didn't want to admit it. It seems that the seals in the pistons had failed and were allowing brake fluid to creep onto the friction surfaces over night. The callipers always have a build up of black brake dust but when dry it could be seen that it had an oily texture that was not obvious when wet with rain. The brakes would even work reasonably well in the rain but fail in the dry, they would genuinely sound like a fully laden freight train coming to a halt!

2 New callipers later and everything is still tickety-boo a couple of weeks on. To change the Shimano Zee callipers is pretty easy, just make sure you have a bleeding kit and plenty of brake fluid. The rear calliper gave me a bit of grief as the banjo bolt rounded off where the allen key fits (they are super tight!), however a slot made with a hacksaw allowed me to use a regular screwdriver to remove the bolt.