brake disc

Every little thing means something…

And the challenge is twofold. One: not ignoring it, thinking oh, it’s nothing, and two: finding out what is actually wrong. Oh; maybe I should say triple fold, because sometimes, unconnected things are connected in ways you hadn’t thought about…

Let me tell you a story of a tiny observation (that I had largely ignored) that could have had serious consequences. My old runabout car passed its government safety test only a few months ago and after repairing a few issues all was good. But, recently I’d noticed the car doesn’t ‘creep’ quite so much. Any automatic drivers out there will know what I mean. When you take your foot off the brake pedal on an Auto, they creep forward. This helps hold the car from rolling backwards on gentle inclines etc.

Then I was facing challenge one. Oh, it’s ‘no biggie’ I thought, it’s an old car, it’s probably just the gearbox getting a bit ‘tired’. Fast forward a few weeks it was time to change the wheels for the winter ones and I found a problem. One of the rear brake disks had a crack in it. Right through.

cracked brake disk
A brake disc like this is not good obviously, the unusual, lighter colour rust is also an indicator of excess heat build up…

Uh-oh I thought, but still, it’s an easy swap methinks. I order a new disc, pop it on with some new pads and away we go. The very next day we had an even larger problem. That brake was jammed on! Sh*t, what did I do wrong I thought?

So, off came the new disc for a deeper look at the calliper (the part which moves to pull the brake pads onto the disc). When I had put a new disc and pads on earlier, I had pushed the piston further into the calliper (to allow for the extra thickness of the new stuff). Unbeknown to me, this pushed the rubber seal onto a rusty area of the piston. And now the piston was stuck, I couldn’t move it at all. It’s supposed to slide back and forth a little you see.

If you’re not familiar, brake callipers have a metal piston inside them with a rubber brake fluid seal and a dust seal. The brake fluid pushes on the back of the piston and pushes against the brake pad, forcing it onto the brake disc, slowing its rotary motion down.

What happens over the years is two things, moisture gets past the dust seal and brake fluid absorbs a little water. These two things lead to rust the outside of the piston, causing it to drag over the rubber seal and either leak brake fluid (bad) or it can cause the piston to stick in the body of the calliper (also bad).

new versus old brake calliper pistons
New vs old brake calliper pistons. Just imagine, the square rubber O ring was trying to keep a seal up against that rust…

Working backwards, I looked again at the uneven wear on the old brake pads (which I’d wondered about but stupidly and conveniently ignored when I put on the new disc), it’s obvious to me now that the brakes had been “binding”, or catching for a while. This extra friction causes heat, oh. A lightbulb moment. The extra heat is what caused the original brake disc to overheat and over time, crack. Duh.

Now comes the bad news. Some car repairs need to be balanced, which means it’s usually wise to replace safety related things at least in pairs, so the items work the same on both sides. I’m sure you can see the logic of the brakes ‘pulling’ with the same amount of force on both sides of the car, or not pairing a new tyre with a worn out one, for example…

Plus there is an assumption of age related wear. Not always, but with parts which are considered “consumable”, nearly always. A window winder motor for example, could be replaced singly as it might just be a bad one or usually the drivers as this is used the most. But with 17 year old, original brake calliper pistons, as in this story, not so much. If one is rusted, there is a better than even chance that they all are.

brake calliper repair kits
New brake calliper repair kits with new pistons, rubber seals and dust seals with retaining clips…

Off to the store then for four sets of new brake calliper pistons, rubber seal kits and some new brake fluid. Now everything is rebuilt with new brake pads and the car drives so, so much better, more responsive, brakes better, pulls away better, holds on inclines better, the whole nine yards.

inside a brake calliper as good as new
Although rusty on the outside, this 17 year old brake calliper body is as good as new on the inside where it counts…

In addition to a brake just jamming on, which was obvious. I now realise that all of the rusty brake calliper pistons were not releasing the brake pads as quickly as they used to. This was causing a tiny amount of ‘drag’, a little extra friction. Not enough to make the brakes not work, they did stop the car okay and even passed the test. But enough to just hold the gearbox from creeping as it normally would.

The answer to the lack of ‘creep’ was a series of connected facts. Rusty calliper pistons were not retracting properly in general, which caused very slight brake binding in general. One rear brake was binding badly, creating heat which cracked the brake disk which caught my attention. The slightly binding brakes were the reason for the lack of creep from the gearbox. Problem solved.

So there you go, one failed observation. The moral of this story is don’t ignore the little things, they always mean something has changed, and only rarely for the good. Check stuff out at your earliest convenience and try to make connections. You might just save yourself from an even larger bill later (imagine if my brakes had leaked and failed!).

Merry Christmas to you all, it’s been a terrible year for sure, but lets hope that 2021 turns a real corner this year and we can go about picking up the pieces of our old lives.

Stay well


Comments 1

  1. Hi Ian,
    As always, look for the cause of the problem, not the effect. LMAO, done the same thing myself with electronic gear, its easy to just change the fuse, but I always ask myself (now) Why did the fuse actually blow?
    Glad to see you are still alive and kicking, and still learning new things.
    With kind regards, Michael

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