SOHC.co.uk Forums > CB500/550
Re: Brake caliper re-assembly electrolysis worries
K2-K6:
You can just get small pot size from plumbers merchants or something like this
https://www.amazon.co.uk/PROUNOL-Silicone-General-Purpose-Dielectric-Waterproof/dp/B088361TCJ/ref=psdc_303918031_t2_B086QBNSRT
It's generally very useful anyway for all sort of things as inert to most materials, and so safe to use.
Particularly good on electric connections on old Land Rover systems too. ;D
deltarider:
Car mechanics use this.
Bryanj:
Not in UK we dont just copperslip. You wont find many car mechanics rebuilding calipers usually exchange rebuilt ones are fitted due to cost of labour
McCabe-Thiele (Ted):
--- Quote from: florence on June 06, 2021, 06:14:21 PM ---well, I have assembled the brake caliper, very easy and quick but suddenly realise I may have made a mistake. The new piston is stainless steel rather than the original chrome steel type and therefore will be prone to electrolysis with the aluminium and the bike spends most of it's time outside. Although the old type of piston goes rusty after a few years, it doesn't affect the caliper. Has anyone had problems with this and should I order an original piston?
--- End quote ---
Galvanic corrosion as you know occurs when two disimilar metals are in contact so both types of caliper metals will have this issue be it your new stainless steel calipers or the original chrome/steel type.
On the outside you will have water / salt road grime helping the corossion process on the inside you might have water if you are using mineral brake fluids due to the hygroscopic nature of most brake fluids. Certainly on cars it is my experience that calipers seize or stick due to moisture getting past the dust seals causing the chrome to pit etc.
K2-K6:
"Certainly on cars it is my experience that calipers seize or stick due to moisture getting past the dust seals causing the chrome to pit etc."
That's one of the issue here, they have no external seal at all, dust or otherwise.
It's just straight into the bore between the piston and caliper until it meets the only seal. You get a creeping corrosion that also travels round behind the seal into the machined groove, ultimately compromising the seal ability to retract the piston in use and resulting in brake binding.
The silicone greaee is the external protective boundary if they are assembled dry (no fluid) with it.
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