Can you tell why this caliper has gone?

Question

Mechanic told me one of my calipers has gone and this caused accelerated wear to relevant pad and all that's left is metal. You can see only metal in the pic 1 of pads as compared to the good brakes in pic 2.

1) I didn't understand why he said the caliper needs replacing. All I remember is he said 'look the disc on that one is red'. From the bad pic can you explain what's wrong with the rotor and if it does indeed need replacing? why did he point out that it's red?

2) All other discs, calipers and pads are fine. With the faulty caliper due to metal screeching on the disc, there are two circles lines which I can feel going around the disc when I put my finger on. Maybe you can tell in pic 3. Does this rotor need to be replaced? I will probably sell this car in a 1-3 months and have spent endlessly on repairs so I'd rather not buy the caliper unless it's really required even though I know their cheap.

Edit: yes, this question is about the rear left caliper and disc shown in pic 1 and 3. Pic 2 is rear right caliper which I imagine is fine. Also the answer isn't clear to me.

I understand one pad is worn so I will need to change back two pads for balance, but why all 4 pads? Also does the brake disc even need to be replaced(is it a must or just recommendation) and if so is it just the one I need to change, if more why? Is it just the one caliper that needs to be changed, or can I keep it and just change the pins on it as somebody mentioned? please clarify.

Answer 1

Clearly one of the four brake pads is worn. All four need to be replaced.

• Its not totally clear on if this is a front or rear wheel. My guess is that this is a rear wheel, and you use your parking brake when you park your car. And one day you forgot to release the brake while driving away. That will DEFINITELY wear just one pad (I dare you, ask me how I know, sigh...) Parking brakes on four wheel discs are just an odd duck. It doesn't take long to wear down a pad in this situation. One time driving will do it...

• Another contribution to uneven brake pad wear is the caliper assembly may not be free to float (to self center) Its possible there is excessive wear on the slider elements and a groove is worn, stopping further caliper centering. This will definitely cause one pad to wear out before the rest. This can occur on either front or rear brakes. On your brakes, the sliding elements are located underneath those corrugated rubber boots. You can easily purchase replacement slider pins, they cost just a few dollars.

• I believe the comments about the rotor being red refers to excessive steel being worn off the rotor. That wear propogates as metal 'dust' and when that rusts it goes red. Obviously the rotor with lots of wear will be rust red.

• And as for machining the rotor? Best recommendation is to either machine them clean (and ensuring there is enough residual steel remaining on the rotor per spec) or replacing them. I suspect a new rotor will cost $45 or so. My recommendation to you is to replace or regrind all when you replace the pads for best performance and safety. I know others may bypass a replace/regrind if the wear is slight and on the rear wheel. If these are on the front wheel, you will definitely need to replace or regrind the rotors.

Good luck with it...