Aluminium brake caliper pistons

[Brummmie]

I had some trouble at Donnington last weekend with the brakes binding on, causing loads of heat...
I now have the replacement Stainless pistons in today, so i have stripped down the Alcon Race calipers and its clear to see what the problem was.
I have even used autosol with a soft cloth to polish the piston to seal area, sad i know but if a jobs worth doing!?
Upside is the 330mm discs dont look fazed by the silly heat that was being generated..

[FarmyardPants]

So.. what are we looking at in that picture exactly?

[Brummmie]

FarmyardPants said:

So.. what are we looking at in that picture exactly?

The great big band of corrosion on the piston?

[FarmyardPants]

Ok I noticed that, so the bottom one is the new one that you polished even though it's new, and is a direct replacement for the other one even though it's a different length? Not trying to be clever (for once) just wonderin

Edit: I see now that the lower one has a polished left side, didn't notice that earlier

[Brummmie]

FarmyardPants said:

Ok I noticed that, so the bottom one is the new one that you polished even though it's new, and is a direct replacement for the other one even though it's a different length? Not trying to be clever (for once) just wonderin

Edit: I see now that the lower one has a polished left side, didn't notice that earlier

They will still go in they also have knock off springs behind, the calipers are just two years old with no salt use..

[FarmyardPants]

As an aside, whatever rubber-like compound is used for the piston seals - can we use it for the clutch slave piston? Can't understand the disintegration of clutch components when brakes have a much harder life and are so much more reliable. If my brakes failed as often as my clutch I'd have used up more lives than my cat! Makes no sense to me.

[Boosted LS1]

Some race calipers don't have the dust seals that road calipers have which is why contaminants can get in there.

[Sardonicus]

That's how most calipers fail (binding) due to piston corrosion dust seals or otherwise be it Nissan Micra VW Golf etc etc I presume in the title of this thread you was referring to the caliper body material rather than the piston as that looks like plain old coated steel to me standard on most OE

[Brummmie]

They are Aluminium pistons, like i say just two years old summer use only, so my point Beware if you are getting new calipers with aluminium pistons, as alot of the top end calipers are.
This full set of stainless pistons will sort it but its additional cost, and it put a premature end to my track day (my one and only this year) drove home fine, as the heat is nowhere near.
Alot of us guys out there have 15 year old AP Racing calipers..

[Getsis]

1st thought is why would anyone use an aluminium piston that is in contact with moisture, air and heat?! plus the seal will rub off the oxisised surface on a regular basis leading to rapid corrosion? only reason I can see is they would be seen as a disposable item after one or two races. Stick with St. Steel if you don't intend to replace them on a regular basis.

[Sardonicus]

Brummmie said:

They are Aluminium pistons, like i say just two years old summer use only, so my point Beware if you are getting new calipers with aluminium pistons, as alot of the top end calipers are.
This full set of stainless pistons will sort it but its additional cost, and it put a premature end to my track day (my one and only this year) drove home fine, as the heat is nowhere near.
Alot of us guys out there have 15 year old AP Racing calipers..

OK my bad most aftermarket performance calipers for as long as I can remember have always been needy IMO anyway aly is not ideal material for brake calipers anyay apart from the weight saving this is why you will find motorcycle brake calipers need far more attention and upkeep than good old cast iron found on 90% of cars on our roads, VAG ally rear calipered cars are notorisisly troublesome because of said material