On my last ride my rear brake had become pretty useless I think I could have gotten more braking if I had squeezed my finger and thumb around the brake disc.
Now this was the first bike I had ever had with disc brakes so I hadn't really got a clue, however I have done motorbike disc brakes so how hard can it be... ahem
The first thing was to diagnose the issue and this was what I came up with:
1. The rear brake cable was contaminated (there was a lot of drag when pulling and it wasn't returning properly, I suspect it got some sea water in it.
2. The rear disc was contaminated, just wiping a tissue over it left black oily residue
3. Because the disc was contaminated I was pretty sure the pads were contaminated.
Stage one: I disconnected the brake cable and removed it from the bike as well as the sleeve. I cut off the crimp at the end and pulled it out of the sleeve. Sure enough it had contamination and corrosion, it was dull etc.. I laid the cable on some paper and I sprayed it with a light oil, I then fed it back into the sheath and worked it backwards and forwards.
I then oiled the new cable and threaded it through, the new cable glided easily so that was one issue resolved. I refitted the cable and but didn't connect it onto the disc brake lever at the rear.
Stage 2: Decontamination
I removed the rear wheel and took it outside, I put sprayed the disc surface with disc cleaner and then worked it in with tissue. I did this to both sides then wiped the disc thoroughly, I did this two times until I was getting no more residue or contamination off. I left the rear wheel outside for a while so the solvent on the disc could evaporate thoroughly.
Stage 3: New Pads
To fit my new pads I needed to remove two retaining bolts on the inner housing, this allowed me to remove the existing pads, i could see clearly they were contaminated. They are only held in place by magnets so it's not a hard task.
Once the old ones were removed I examined the mechanism it seemed ok but I applied some lubricant to the moveable parts, it moved even more freely now. I then fitted new pads in and replaced the two bolts.
Stage 4: Adjusting:
The first stage in adjusting my brakes was refitting the wheel and then I fully tightened all of the brake adjusting nipples, on the rear brake and the adjuster on the brake itself so I could get the maximum adustment later.
I then moved the rear brake lever and refitted the brake cable, keeping an eye on the outside pad I pulled the lever and adjusted the cable tightness so that it left the outer pad 1-2 mm from the disc itself. I just checked the manufacturers website and they recommend 3mm gaps either side of the pad, I will try that later see if it makes any difference.
I then turned my attention to the inside adjuster, between the bolts that I had removed to fit the pads earlier. I tightened this so that the inside pad protruded towards the disc, again leaving 1 - 2 mm clearance from the disc. I then turned the pedal to ensure there was no catching on the disc.
I made the wheel go faster and then pulled the rear brake, it bit very well but the bite point was at almost full extension on the brake lever. I slackened off the brake arm lever and then removed some of the slack on the cable bringing the disc slightly closer.
I then cranked the wheel again and pressed the brake lever, it was an amazing difference the brakes felt like new.
Now I should mention this, that when I went for the new cable I showed it to one of the "bike mechanics" he told me I would most likely need a new disc/pads and possibly a new rear brake as the tightness on the cable was likely to be a damaged brake mechanism. I knew enough to know a new brake would not have been necessary, if it had I would have made a warranty claim!!
In the end, it cost me some spare time, a brake cable £3.99, some cleaner £4.99 and a new set of Pads £12.00 front and rear. Had I gotten the shop to do it.... I would have paid top price for the parts and labour of about £40.00 per hour... This is why I like to maintain the bike myself, it's fun, saves money and best of all makes me better able to deal with on road emergencies myself!
I will try and take photos to add.