Brake weirdness

[Visitor Q]

Hi guys. My rear brake is being a funny little bugger.

A while ago it started to feel piss weak, like it was barely having any effect.

I eventually got round to getting in new pads and fluid, and swapped/bled. Anyway, never got a go to test it until today due to sump stupidity.

Anyway today I sorted everything, went for a ride and was excited to try to the new pads.

Same cunting shite. Went through tesco carpark with the back brake on reasonably hard (well, pedal pushed a fair bit) and it barely affected the ability to go forward.

Got back assuming it was obviously not being clamped, touched the disc... in short, its getting clamped very well.

So, do you guys reckon its just the disc has some oil or something on it? I do have a spare disc, but its very rusty and I'd rather not go to all the faff just to rule that out.

Any ideas?

It feels like heat fade (ie you get resistance at the lever but no stopping power), but from the start.


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[4Stroke]

Weird indeed.

I'd go with the oil/wd/whatever and check the pads for discolouration.

Wipe the disc with a white cotten cloth or clean paper towl see if any dark/black greese or anything of that nature comes off.

[Vincent]

Can you still move the bike from a standstill while putting the rear brake on? if you can, it might be something else rather than the pads, seized Master cylinder maybe? Wouldn't hurt to use a bit of brake cleaner on the disc, or anything that breaks up oil and evaporates - thinners etc. You can usualy tell by looking if the pads are contaminated, look for small brown shiny patches on the surface or larger damp looking patches.

[Visitor Q]

[Phoenix]

How thick is the disc? If it's too thin then the pistons might be at the limit of their travel just as they touch the disc so they heat it up but don't actually stop the bike.

[el_oso]

alcohol and paint thinners/white spirit also work particularly well at cleaning crap off the disk. even petrol may work

[sickpup]

Clicky

Simply because if it's not working it's probably seized and I doubt you've ever cleaned it out. Lube the lever pivot point as well.

[Visitor Q]

I've tried the brake from stationery, locks solidly and won't move an inch...

Disc has a slight lip, but only ~1mm, certainly not a beast.

Sickpup I'll bare that in mind, that is fairly cheap to replace the piston too. How about just the seals? When I changed the pads I brought the piston almost fully out, and there was no pitting etc so I don't think I'll need to replace it. But whacking in some new seals might be worth the agro.

I'll relube the pivot points, but fairly certain they were nicely slathered.

Going down the gym now but will sort it out when I get back. Any other ideas while I'm at it?
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China traffic/travel bike vid - When I make a sweeping statement, please add the word 'statistically' in to the sentence before you bitch...
From September 2014 to January/February 2015 I will not be using any English, nor reading any. As such, I won't be on here. PM at will, but I won't be checking/posting unless in emergencies. Certainly not for the first couple of months. Please berate me savagely if I break that rule...

[Visitor Q]

Righto, haven't given it a go yet as I did it quite late.

Cleaned off the disc thoroughly with Isoclene (diluted IPA) and got the dremel sanding attachment out on the pads.

They had quite a weird looking polished black face, which came off very nicely with a quick once over with the dremel. They now look new again, so I'm thinking it was just an inordinately greasy disc.

Wheel still moves fairly freely with back brake slightly applied, as it did with the greased pads. But I'm hoping thats them not bedded in yet.

Will let you know if its any better, and if not I'll need some more brain storming as everything /seems/ to be ok.
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China traffic/travel bike vid - When I make a sweeping statement, please add the word 'statistically' in to the sentence before you bitch...
From September 2014 to January/February 2015 I will not be using any English, nor reading any. As such, I won't be on here. PM at will, but I won't be checking/posting unless in emergencies. Certainly not for the first couple of months. Please berate me savagely if I break that rule...

[The Artist]

I suggest going fast with back brake applied lightly and pump it a bit, warm everything up and bed them in properly.

If that doesn't work, master cylinder probs.

[Phoenix]

Holding the brake on while riding fast isn't how you bed in pads, just likely to glaze them and make them even more useless.

[Visitor Q]

Brake was much much better today, very handy considering the amount of hill starts I have to do on the commute.

Will leave it to bed in, but its pretty much at the level I need now. I quite like locking the rear to swing the back in, but I'll cope without that for now
____________________
China traffic/travel bike vid - When I make a sweeping statement, please add the word 'statistically' in to the sentence before you bitch...
From September 2014 to January/February 2015 I will not be using any English, nor reading any. As such, I won't be on here. PM at will, but I won't be checking/posting unless in emergencies. Certainly not for the first couple of months. Please berate me savagely if I break that rule...