why do brakes seize?

[cadetchris]

this has confused me for a while, why do brakes seize on after a long time standing?

i always presumed that the presence of brake fluid kept the bores in good nick and that piston didnt seize in the bore due to it being a fraction of a nat from the bore itself, so corrosion processes wouldnt be educed by interaction of steel and what every some bores are made from.

but having enjoyed the pleasure of seized brake cylinders recently, i am still not sure why this actually happens.

[polo2k]

brake fluid is hydroscopic which means it activly pulls the water out of the air (sometimes via the seals) and into the fluid. once its in there a bit of corrosion gets going and then its all downhill from there

[bmcecosse]

The very expensive Silicone brake fluid is not hygroscopic - but it has other problems.

[les]

Those problems must have avoided me then, Roy!

[bmcecosse]

Well - it must only be used with a complete NEW set of rubber parts in the brake system - it's EXPENSIVE - and some say it doesn't give a 'hard' brake pedal - in other words - it's slightly compressible. As far as I know it's not used by any new car manufacturers.

[les]

Ah, only problems if not prepared correctly then!

[bmcecosse]

Indeed!

[beero]

One way to help stop corrosion is to flush the hydraulics with new fluid every couple of years.

[DAVIDMCCULLOUGH]

Add to that the back cylinders are made up of 2 different metals!

[Alec]

Hello Cadetchris,

"One way to help stop corrosion is to flush the hydraulics with new fluid every couple of years."

This is recommended as the absorbed water also lowers the boiling point of the brake fluid which can boil due to brake heat and the brakes no longer work as with air in the lines.

Alec

[LouiseM]

Chris - I've moved your message to the 'mechanical' forum as it is more appropriate than 'general discussion'. I've also amended the title as your original title "why do?" gives nobody any idea of what the post is actually about. If you give an indication in the title of what the thread is about it makes it easier for those looking for a thread on the same subject to find it later

[mike.perry]

The back brakes seize because owners park them with the handbrake on over the winter.
Series MM wheel cylinders are prone to seizing if they are not used regularly.
The drums should be removed at service intervals and the wheel cylinders checked whilst an assistant gently presses the brake pedal