This has been another of those new experiences for me, I learned as I went along the right way and also the not so right (or not so easy / necessary) way to do things…
My mountain bike has Magura hydraulic brakes, nothing unusual for a mountain bike, but not something I had ever had the courage to do anything with myself when they weren’t working as well as they should. I don’t think this has anything to do with the fact that they are Magura brakes, all hydraulic brakes need maintenance or occasionally have problems when frequently used in a harsh environment (such as muddy trails), these particular brakes have worked brilliantly for me most of the time, only recently the left hand trigger has been getting closer and closer to the handlebar which meant less room to pull on the brake hard, I knew I had to try to do something about it so off to YouTube I went for some bike maintenance advice.
The first video I watched advised having two plastic syringes, one to pump fluid into the system (via a bleed nipple which is to be attached at the brake calliper) and the other to catch the fluid coming out of the other end (at the handlebar lever), it all seemed relatively easy so even I could manage it. What I managed to do was purchase the wrong kind of syringe (a local shop sold me a farming syringe with a metal tip, I later learned that a plastic tip is much better for this task), spilled what seemed like a lot of brake fluid – it’s just mineral oil but is quite toxic if swallowed so needed cleaning up sharpish from the kitchen floor – and probably spent money that I didn’t need to on a bleeding kit.
Cut to the chase – here’s what I actually did that sorted out my problem, which was probably just a bit of low pressure in the hydraulic system for that lever (the back brake), after watching another YouTube video (which was shown to me by a local bike shop as an alternative method for bleeding the brakes, wish I had seen it to start off with!):
- I slackened off the bolts keeping the lever in position so that it could be swivelled up to an almost horizontal position,
- tightened the lever adjustment screw so that the lever was closest to the handlebar,
- removed the screw / cap (it is a special screw so be very careful not to lose or damage it),
- push a syringe containing suitable mineral oil firmly into the hole,
- then push and pull on the syringe to force the oil in and out of the system, while also pulling on the brake lever several times.
I repeated this push/pull technique for a few minutes, during which I saw air bubbles rising into the syringe, clearly they were in the system from my earlier botched attempt; once they were out and I was happy that the lever was giving good pressure (and the syringe is not under pressure itself, i.e. I had not pushed or pulled on it hard, but it was at a mid-point), I removed the syringe from the hole while doing my best to catch the oil that flowed out a bit using a piece of kitchen roll, then fitted the screw back into the hole with just enough firmness to tighten it without breaking anything (perhaps 3nm or less).
The brake lever should not touch the handlebar when pulling with normal pressure, it should stop about 10mm from it; I did wind out the levers about two turns of the screws in order to give more lee-way for a really firm pull on the lever before adjusting the levers back to their original angles.
Job done, and all I needed was some mineral oil and one large plastic syringe (I actually purchased mine very cheap from a local farm equipment shop, they are designed as use-once-throw-away items for use with farm animals most likely, but similar ones can be found on eBay for about the same price). For mineral oil I splurged on Magura Royal Blood, which is just blue mineral oil from what I’ve been told; thought I might as well stick with what’s already in the system.
This method would probably work for most normal mountain bike hydraulic brake systems, it’s just fluid and air after all, although there are some makes/models that have special requirements so best to consult advice before making any purchases or attempting anything, and check more than one YouTube video on the subject for your exact system.