Leaky Brakes

I got a surprise this morning on my cycle to work. Heading down my first hill towards some traffic lights I started to pull on the brakes: a little on the front first, a bit harder, then pull on the back. The problem was as I pulled the lever for the rear brake it came right back to the bar and nothing happened. That's odd I thought. Luckily there's more than enough power in the front brake to stop easily (although a little tricky if you need to signal right at the same time). I had been away for work the previous week so my bike hadn't been ridden for around a week and a half, but it was still a surprise for the rear brake to fail completely like that.

Earlier on this year I upgraded my brakes to a pair of Shimano Deore XT M775s. I hadn't had any problems with them until now, all in all they have been pretty awesome. At work I checked the lever and calliper for signs of a leak but didn't find anything. At home tonight it was time to find the issue. I gave the lever, line and calliper a good going over, but still couldn't see any traces of oil. There was also no pool of oil on the floor where my bike had been sitting. Off came the reservoir cover and I wasn't particularly surprised to find the reservoir almost completely empty. It was a bit of a mystery, but there was not a lot else to do other than top things up.

With the reservoir topped up and a few bubbles worked out, things were starting to feel a bit more normal. Happy with the feel in the lever I replaced the diaphragm and cover, before rotating the lever back to its correct position. However, that's when the problems began... A quick squeeze of lever resulted in oil pissing out the side of the lever from under the reservoir cover. Annoyed, I went through the process of filling the system back up and making sure I tightened the cover as much as possible. Same problem. Bugger.

I was really at a loss, was there a problem with the cover? Was this the cause of my mystery failure? A bit of googling didn't turn up much and after a bit of looking around and checking the lever over I still couldn't get the cover sealed properly. While looking about online I noticed that most pictures of the levers had the covers positioned the other way around from mine, with the "Deore XT" readable from the front. With nothing else to lose I tried the cover on the other way around a everything sealed ok.

With the brake back together, the lever nice and stiff, and most importantly no leaks, I'm now a bit confused. Does it matter which way the cover is on? If so why doesn't my front brake leak? Is it just tricky to seat the cover and I got lucky? Who knows, I'm just happy that it was fixed without buying any more parts. I'll need to keep and eye on it over the next few days, but hopefully it's now sorted.

So, if you've got a M775 lever which is leaking from the reservoir cover, try it on the other way around and see if that helps.

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