This is my first post on this forum so I thought I’d try and make it a useful one. I’m new to MTBing but I like to fix things myself, so after watching many bleeding videos on Youtube I decided to take the plunge and bleed my own brakes. I bought an Avid kit for this job. Here’s a few things I learned from doing ‘first-time’ mistakes.
When it says fill one syringe half full, I recommend filling it 3/4 full. The reason for this is that when you de-gas the syringe it’s quite difficult to not lose a lot of fluid while forcing the air out of the tip. During my first few attempts the fluid went flying out of the syringe and all over the floor! If you manage to do a decent job and not lose too much fluid, then you can always dispose of some to make sure it’s only half full as instructed. The last thing you want to do is de-gas the fluid then realise you’ve lost too much and need to refill and de-gas again.
When creating a vacuum you may find that there isn’t much room left in the syringe to draw the air out. If so, simply pull the syringe back as far as you can and leave it for 10 seconds. You’ll start to see bubbles making their way through. There’s no need to keep pushing the syringe back in and out as quickly as it mentions in the service manual.
Wear glasses. Period. When removing the syringe from the bleed port it flung some fluid into my eye. Not nice. And definitely wear gloves because no matter how careful you are you’re bound to get some on your hands the first time you try this, especially when removing the syringe from the bleed port.
This is probably the most important tip. If you have spilled any oil onto the floor then make sure you reinsert your pads AWAY from that spill. I was careful throughout the whole bleed process not to get any oil on the pads, then at the last minute I dropped a pad onto the floor and straight into a patch of oil. Even if you clean up the oil patch straight away, there will still be residue. Simply move your bike away from the spill before re-inserting the pads.
Anyway, that’s my tips from a bleeding newbie. It wasn’t as tricky as I thought, but at the same time, some aspects were more difficult than I imagined.
Now, a question for you bleeding experts: Is it possible to bleed the brakes without using more fluid? Can I just add a small amount of oil to a syringe, then jump to the stages where you create a vacuum and fix the lever against the handlebars? The reason I’m asking is because I don’t want to waste oil, plus it’s pretty nasty for the environment.
Not sure about replacing the bled fluid so I’ll let others weigh in. However, if the fluid has been in the brakes for a while, chances are there could be some contaminants in the used hydraulic fluid. But if it looks just like the new stuff (same color, and clear) I would think it would be possible to reuse the fluid, but like you said, you may need to add just a bit due to any losses.