brake piston maintenance

[czakal]

It's the middle of summer, but as a commuter I have to ride in all 4 seasons and I'm thinking ahead about winter preparation a bit. With my previous bike I had trouble with a brake piston becoming stuck due to corrosion. When riding in winter it would be important to keep all such parts clean and dirt/salt free, but I don't know if that's easy to do with the brake unit? I haven't even disassembled one myself--is it usually possible to access the piston in order to inspect/clean it, without needing specialised tools and equipment?

Seb

[fatpies]

What do you ride? If you ride a single disc machine then brakes are easy. Just undo the caliper. Remove the brake pin, and then pump the brake you'll notice the brake piston come out a bit.

You can either pump it out fully or pump it out partially and clean around the piston. If you pump the brake too much the piston will fall out. Try to get them both out as far as possible so you can pull the piston out which doesn't fall out. Clean it. Take out the seals clean them up or replace them. Clean the pistons looking for burrs which you can flatten out with a bit of plastic. Then put the seals back in push the pistons back in and then bleed the system:

You need:

A Hex key for the brake pad pins.
A spanner to get the caliper off
A length of hose to fit onto the bleed nipple.
Brake fluid.

[czakal]

Thanks for the quick reply. For those who don't know me--I ride a Kymco Pulsar (2010) which in most ways is like the CG and it has a single disc on the front wheel. Most instructions I found for working with the brake (mainly, about changing the pads) says not to press the brake lever when the pads are out, but I guess you have to do that to get the piston out to inspect it. I'm assuming you have to remove the pads to get access to the unit. From what you say, you also have to bleed the system each time you work on the piston?

Seb

[fatpies]

[dangerousdave]

Hi Seb,

If your brake is working fine at the moment then it wont require drastic maintenence.

What tends to happen with hydraulic brakes is road crud builds up on the sides of the piston, which corrodes the piston and damages the piston seals.

You can do an inspection and light clean up of the brake without having to remove the pistons, and therefore not having to refill the system with hydrailic oil. If you do this regularly, then you wont ever have a piston seize again.

You can remove the caliper from the fork (while keeping the hydraulic cable attached), remove the brake pads, pump the lever to push the pistons out half way, and clean them up. Remove any dirt, and clean up the pistons with brake cleaner. If there isn't any rust on the pistons, then push them back in, reassemble and you're good to go.

If the pistons show corrosion then they will need to be replaced at some point, as this will damage the seals and cause leaks. However, minor rust will likely clean up well enough, and not be a concern.

Does that help at all ?
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1988 Kawasaki KMX 200

Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50

[Ade75]

The problem with your previous bike could have been down to a split piston seal which would have been letting in water/salt and corroding the piston. Check out youtube for some 'how-to' video's on how to overhaul a brake caliper.
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CBT Passed: 05/10/16 Theory Passed: 13/10/16 Mod 1 Passed: TBA Mod 2 Passed: TBA

[prawny1]

Most of the time when brakes sieze up it is due to corrosion behind the seals rather than on the piston body, sometimes the caliper slides stick too.

The sealing point of the fluid seal is on it's deepest edge inside the piston bore where it is angled.

Youably looking a good 6 or 8mm down so minor pitting on the edge of the piston is not normaly a problem especialy when you consider the pistons are pushed out a few mm even on brand new pads.

Sometimes if the brake fluid has never been changed the fluid can form a kind of crystaline deposit behind the fluid seal too.

If you want to keep your caliper healthy you need to at least clean out and regrease the dust seal grooves with rubber grease, the grease will help prevent water creeping in again and keep the piston nice and free.
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[TUG]

Heres what happens, simple version:-

Road salt reacts with all metals on the bike - Corrosion and rust occurs.

Brake calipers are aluminium, salt corrodes.

Corrosion then occurs in the seal seats pushing the seal against the piston, this causes binding (brake pad always touching disc).

If not cleaned out at this point, more pressure will be applied to the seal against the piston until it then gets pushed out, the caliper piston can no longer return even with pressure from you.


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Haz ER-5, innit!

[czakal]

Thanks for all the advice. This will help me do better preventive maintenance on this bike.

[Robby]

Don't be worried about leaking brake fluid. It isn't difficult to drain down and refill the brake system.

Brake fluid should be changed every two years anyway. New brake fluid does make a difference. It always amuses me when people fit braided lines to their 5 year old bike and say how much of a difference it has made, when most of that is just down to replacing 5 year old fluid.

[TUG]

[czakal]

Gadgets have their uses, but I don't think they help much if you skip regular maintenance.

Seb