Disc callipers ser 2 1969

[C Kyte]

Hi, for years I have been experiencing calliper pistons siezing in calliper. About every 4 to 5 months I push pads and piston back onto calliper to prevent seizing up. I last kitted all callipers 2016, can has traveled 3,199 miles, [ 5,148 klm ]. I have stainless steel pistons, don't know if that's what is causing it. Callipers are full of sludge, must have moisture in fluid. Looks like I will have to go through the whole brake system and clean it all

Chris

[bitsobrits]

Stainless pistons should have no impact. Sludge in the system implies infrequent brake bleeding, and perhaps seal degradation from using non OEM quality seals. Brake fluid becomes moisture contaminated with age, even if no miles are driven, and for that reason a thorough system flush every 2 years is good practice.

[abowie]

The high humidity in Brisbane might be a contributor, especially if you don't drive the car very often. Water absorbing into the brake fluid gets boiled out in a daily driver, but not so effectively in a car only driven a handful of times a year.

One option for you would be to run silicone brake fluid instead as it is not hygroscopic. If you're going to overhaul the whole brake system consider this as an option.

Cheers

AB

[Series1 Stu]

Hi

Stainless steel pistons might be a contributing factor, especially if you have high humidity. If the pistons are made from a 300 series grade, which is likely, then there is an increase in potential difference between the stainless steel and the aluminium calipers giving an increased risk of galvanic corrosion where the aluminium will oxidise more quickly.

If the pistons are made from 304 grade stainless, which is likely, and the humidity is high then the pistons are at risk of stress corrosion too. Brisbane being coastal possibly adds salty air into the equation, which would make things even worse. I've seen dockside equipment made from 304 stainless returned within a month due to stress corrosion cracking. It's an interesting process.

Andrew's advice is excellent. Brake fluid contamination is likely.

Regards

[C Kyte]

Thanks for the replies. The St St pistons I machined them from high tensile St St and they are highly polished. Moisture I think is the problem. Will have to look into using synthetic brake fluid, not sure if you need special seals in system. I cant remember system being flushed since OI overhauled them 2016. I have a big job ahead of me, I have new parts on the way.
Thanks guy's,

Chris

[C Kyte]

Its moisture alright, high tensile St St is magnetic and on the bottom of pistons there were little tiny spots of rust, just re polished 3 pistons.

Thanks guy's

Chris

[Series1 Stu]

High tensile stainless steel? That doesn't really tell us much. Do you know the grade? Being magnetic and having rust spots suggests that is a ferritic grade. You certainly don't need high tensile material as the pistons only really take compressive loads and most materials are much stronger in compression than in tension.

I'm sure you'll be fine if you use silicone fluid although the lubricating properties are questionable. If you've got the pistons out then you'll be replacing the seals anyway.

Regards