In muddy, wet conditions, brake pads wear out very fast. Replacing cartridge type pads is quick and somehow satisfying. I'm a fan of Clarks brake stuff, because quite simply, I've never been disappointed after buying any of their products. I also like Kool Stop, but they are pricier. So, step one, dismantle your brake assemblies, and clean up the alloy holders (soapy water and an old toothbrush - rinse well in clean water, and dry off with a paper towel).
Simply slide them in, but at the point shown in the photo below, remember to put the bolt back in position before fully pushing the pads home. I hold the pads with my fingers and press the holder down on a flat surface.
Put the bits and bobs back on the bolt in the original order, finishing with the washer and nut. Below they are all ready to be fitted back on the bike.
I have to say that I find the Clarks pads to be an improvement on the Tektro pads that came with the original brakes. The great thing about cartridge type brake pads is that you can try out a few different brands and types - e.g. dual or triple compound varieties - in order to find the ones that you most prefer. There's a huge choice out there, and a wide spectrum of prices!