Yesterday, I hoped to deal with a sticky brake caliper on the XM. Initial inspection revealed torn slider boots. The XM uses a single-pot caliper, with a single slider on which the caliper ‘floats.’ The best calipers simply have (at least) one piston per pad, either side of the disc. As on a 2CV, original Mini or Range Rover. These pistons push on the bad when you press the brake pedal, and braking occurs. The only thing that goes wrong is that the piston gets stuck in its bore due to corrosion, which leads to the brake sticking on – lots of heat, lots of wear and an accident if you don’t sort it out. The use of steel pistons (Mini/Range Rover) doesn’t help here. The alloy ones on my 2CV don’t corrode.
Later floating designs cheapen the design by having only one piston. As well as pushing directly on one pad, the pushing power is transmitted by one or two sliders, so you get a gripping pressure on both pads – like your hand crushing a drinks can. Now there is more scope for problems, as these sliders can stick as well as the piston. Again, they can stick in such a way that the brake can’t release – as I once had on my Daihatsu Sirion – or they can stick in such a way that the brake application is uneven – as is the case with my XM right here. That’s because the seals that should protect the slider were torn, allowing muck to get in and damage the slider.
I ordered a new slider, because it seems you can’t order the boots separately. Besides, the old one was probably damaged. I also ordered new discs and pads as the uneven wear had caused one pad to wear very badly, and one side of the disc.
Sadly, I got sent the wrong slider, so this job is abandoned for now. I cleaned up the old slider as best I could, slapped it in red caliper grease, and reassembled. I’m not fitting the new discs and pads until I can fit a new slider. What a pain!
But if you’d like to see the work in action, here is my latest video.