Re: Brake caliper re-assembly electrolysis worries

[florence]

Having taken apart my front caliper and replacing the piston and seal, I am contemplating re-assembly.  I want to put something on the threads of the two large bolts that go through the caliper so that I can undo them next time it needs servicing.  Would a very slight smear of high melting point grease be OK, I don't imagine it will get anywhere near the pads or disk?

[Johnwebley]

Or Copper slip ,that's what I use

Sent from my SM-A750FN using Tapatalk

[florence]

Thanks John, I did think that but I haven't got any and wanted to finish the job today.

[Bryanj]

Any grease temporarily then coppaslip as soon as you get some

[florence]

Thank you Bryan.

[florence]

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?

[Spitfire]

Put a stainless piston in my front brake in 2007, it's still fine, the piston is separated from the alloy by the seal.

Cheers

Dennis

[Bryanj]

Fitted loads and never yet had a problem

[K2-K6]

It needs to be assembled with silicone grease as this prevents an electrolyte forming from water and salt in the gap between the piston and caliper bore. There is no weather sealing on this type of caliper and this takes it's place as best as can be provided.

It's even in the first 750 KO manual as direct instruction.

Don't assemble with brake fluid as lubrication for the seal,  it's hygroscopic (absorbs water) and just promotes accumulation of moisture to facilitate electrolysis. 

[florence]

OK, thanks for the advice, looks like I will have to take it apart again before winter and get myself some silicon grease.

[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. 

[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)]

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?

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.