Bleeding hell

I've always done as much of my own bike maintenance as I can and as a result have learned how to fix, build, repair or maintain most parts of a bike. I find it fun to work out how stuff works, and it's also useful to be able to fix your bike, or someone else's, when you're out riding. However, after a kid came up to me with a separated brake hose last year and asked for help, I realised that I have a significant blind spot when it comes to hydraulic brakes. Having run cable rim brakes for my entire life until this year, I guess that is to be expected.

I've been slightly unhappy with the brakes on my MTB since I bought it and have tried a few things to improve them. "Bedding in" pads and discs was a new concept to me, so I did a quick internet search and gave it a go. Initially I just tried to bed in the rear brake, and it seemed to work. But after a couple of rides the front brake got better and better and eventually was much stronger than the rear. In hindsight I think I overdid the bedding in of the rear brake, and cooked the pads. Cleaning the rotors with disc brake cleaner helped a bit, and replacing the pads helped more, but the rear brake felt pretty spongy as well so I decided to try bleeding it.

Step one was to work out what tools and kit I needed to buy to do a successful bleed. There are so many different bleed kits available and not much official advice about exactly what you need. I have Tektro brakes, and I ended up with two of what Tektro call their basic bleed kit. Most people seem to agree that bleeding is much easier with two syringes, and the basic kit only comes with one. However buying two of them was still cheaper than any other two-syringe kit I could find and I was pretty sure that if it said Tektro on the box it was going to fit my brakes somehow.

Official bleed kits!

 

This is what you get in the box.

Next bit: mineral oil. The shop I found the bleed kits at didn't have any official Tektro mineral oil, or in fact any kind of mineral oil on display. After a bit of waiting around for helpful staff they came up with a bottle of Magura Royal Blood mineral oil, which I was assured would be fine. 

One last luxury purchase: my first ever bike stand. Now I really feel like an adult.

Time to start work. First off, how to get the bike into the stand? I settled on clamping on the seat tube as the top tube is a bit of a weird shape and didn't fit so snugly in the stand clamp. This worked fine, until I took the rear wheel out to start the bleed process. Then this happened:

Never mind. Removing the front wheel as well sorted the balance problems, and once the bike was angled ready to bleed (caliper at the bottom and lever at the top) it was all fine anyway. One thing I hadn't thought of was how to stop the bars flopping around. I didn't have anything the right size to wedge in or tie on anywhere, so settled on doing up the headset preload bolt way too tight to stop the bars moving. It was pretty dark in the cellar, but I had a bike light handy that fitted perfectly on a pipe on the wall. Now it was really time to start work.

One toolbox is never enough.

Step one - wheel out, brake pads out, push the pistons back with a tyre lever and put a bleed block in. Obviously there is no bleed block in the Tektro basic bleed kit. A small amount of swearing later and I managed to get a 10mm allen key to stay in there.

The main part of the process went reasonably smoothly. 

• Rotate the lever so it is level, bleed port facing up. 
• Remove the bleed port screw and make sure the rubber O-ring comes out with it. 
• Screw in an empty syringe using the correct adapter to the lever bleed port. Pull slightly on the syringe so less oil comes out of the bleed port on the caliper when you undo it. 
• Fill the second syringe 3/4 full with oil, make sure you get all the air out of the tube and attach to the caliper bleed port.

Then comes the fun bit. Squeezing the bottom syringe and pulling slightly on the top one starts to push fresh oil into the system. At this point, this is what I saw:

Pink Tektro brake fluid with giant air bubbles; surely this was the source of my spongy lever! Once I'd pushed most of the fluid through the top syringe looked like a bit like a raspberry and blueberry slushy:

Sorry for the terrible photo. It is quite hard to take a photo with a mobile when you have oily hands and have to hold one syringe up and it's quite dark.. As you can see, the new Magura oil is less dense and has floated to the top - weight weenies take note. I decided to ditch the oil in the top syringe, refill with new, blue oil and carry on. According to instructional videos from both Park Tools and Tektro, you should push the brake fluid up from the caliper first, then back down from the lever end, and then back up again, repeating until you don't get any bubbles. It all seemed too easy. I removed the syringes (caliper first), screwed the bleed screws back in, and tested the brake.

Maybe I need a third toolbox.

Spongy. Probably a bit worse than it was before. Damn. I compared it to the front brake lever which of course pulled straight back to the bar with no resistance as the front wheel was still out. Now my front brake pads were stuck together. Rage. I levered them apart with a tyre lever and cone spanner and decided to just reinstall the back wheel and see if it worked at all. First, brake pads back in. After three of four goes at this I dropped the whole lot on the floor, and the spring disappeared. Several minutes of hunting on the floor with a torch later I noticed it was still stuck in the caliper. After finally getting the rear brake back together and wheel inserted I gave the lever a few more squeezes just in case, and once again compared it to the front brake. Whoops. Still hadn't put the front wheel back in. More pad levering followed, and then front wheel reinstallation. At this point I was pretty fed up with the whole process, not to mention hungry, so I decided to give up and try again later. 

Here are my top tips for your first go at bleeding a brake:

• It might not work - don't do it the day before a big ride.
• Make a list of what you need before you go to the bike shop. Include a bleed block.
• If you have a choice of long or short hoses, use the short ones.
• Have somewhere to put small bits, like bleed screws and pads.
• Have plenty of clean paper towels or similar.
• Don't start if you're already in a bad mood.
• Make sure you have lots of time. For a first time I needed around 90 minutes but I reckon it will go much quicker when I try again. 
• Preferably have a cup of tea ready, unless you are miles away from a toilet.
  

If you're reading this and you know what I did wrong, please let me know! Otherwise I'll give it another try at some point and let you know how it goes.