RE-SLEEVING A BRAKE CYLINDER
We will be rebuilding your brake master cylinder today, but perhaps I should start by telling your readers a little about brake calipers so they get a better overall understanding of the work we do – on master cylinders most of the internals are reclaimed because there are so many variants, but we machine our own caliper pistons because every unit that we rebuild gets new ones. We only use British steel for our pistons. These used to be hard chrome plated, but that has been banned under health and safety legislation because of the process involved, so OE went over some years ago to a process called electroless nickel (or EN) plating, and that is what we use too.
Why do the pistons need to be so hard? You’d be surprised at how they wear because they are not just pushing out. Think about the way the wheels are rotating; as the pistons come out, the pads grab a disc that can be rotating at some speed and everything wants to go in the direction of travel. So there is always a thrust side to the caliper, and pistons do wear as a result. Plus, of course, if salt gets in behind the seals, then it will corrode the chrome hardening very quickly.
You can get pistons in plated steel or stainless steel. A lot of people choose stainless just because it won’t corrode, but it is a lot more expensive. The cost of stainless steel itself has rocketed in the last 12
