how do I change brake fluids/brake problem?

[steppen22]

My wheel is still stiff, and I'm getting a little fed up now. I've stripped, cleaned and copper eased the caliper, and I return today and yet again I can hardly move the front wheel with my hand. I really could do without this with my test approaching and u turns, etc, being nightmarishly extra difficult becuase of this. I figure the piston is forcing itself out when the bike is stationary, and I can't think why other than upset fluid pressure.

So I'll need to change fluids. but

a) the screws on my cylinder won't budge. WD40? (but won't this work it's way into the chamber?)
b) I'm not sure what to do. Just unscrew the cable from the caliper and let it flow into a pot. Fill up via cylinder. Or do I need to fill whilst draining - is that what the little nipple under the rubber seal is for?


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[LeeR]

The little nipple is where you bleed the fluid from, get yourself a short piece on tubing, slip it over the nipple and drop the open end into a jug. Now while someone squeezes and holds the brake lever (or you can cable tie it) turn the nipple and bleed some fluid out.

Alternatively just open the reservoir and remove the excess fluid using a pippet/syringe or kitchen roll.
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[TAX MY BRAIN]

As said above bleed your brakes properly, a google search on bleeding brakes will show you how if you are unsure,

You say you have stripped and cleaned the caliper, did you take out the pistons in the caliper ? ?,

im not saying take them out if you havent already,
But if you have, Did you put the piston seals and dust seals back properly, It could be the piston seals not seated corectly that is giving you the problems
all the best

[Cigaro]

I wouldn't remove the brake line from the calliper, you don't really need to do that to change the fluid.

Just get a length of tubing, unscrew the bleed nipple, pop it over the top and then pump the brakes until all the fluid is out. Then take the lid off the master cylinder and soak up any excess fluid with paper towel.

[finpos]

[Ichy]

To undo the master cylinder screws first try the correct size screwdriver, if that doesn't work go for an impact driver, as a last resort https://www.bikechatforums.com/viewtopic.php?t=148055


Do a search for brake bleeding or find someone who can show you how, its a bit risky to be playing with brakes when you have little idea of what to do.

As for the original problem, I've seen the little fluid return hole in the master cylinder get partially blocked with some gunk and cause similar problems, might be worth cleaning it all out.
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[rotax81]

[Ichy]

Out of interest, are you using the bike daily or leaving it sitting? Does it get better or worse when you ride it?
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[Cigaro]

Maybe the problem is that there is too much fluid in, stopping the piston from returning fully?

[Vincent]

Could be that the master cylinder isn't allowing fluid to return.

[Ariel Badger]

That caliper has not been stripped by the look of it. The piston will be gummed up into the cylinder. If you need to ask how to strip one down I do not recomend trying it yourself. I recon it should cost £30 plus parts to sort it.
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[steppen22]

[Cigaro]

What you could try is pushing the piston out as far as you dare (without actually popping it out of its seals), spraying brake cleaner on and scrubbing with a toothbrush. Push it back in and repeat. That's what I did to free mine up (it was still binding slightly but that sorted itself out over time, I can only assume that the pads wore down enough to stop it).