Bleed your brakes: A simple guide to improve your stopping power.
Bleed your brakes. A simple guide to improve your stopping power
Maintenance on your bike’s brakes is important. If you can’t stop when you’re heading to a massive drop-off out on the trails or when a car is pulling out on you, then the consequences could be terrible. So if your stoppers are not working as well as they should, it’s time to spend some quality time in the garage and Bleed your Brakes.
So let’s start this thing off on the right foot. Doing any level of mechanics or maintenance on your bike is vastly easier and more effective if your bike is clean to begin with. There’s a whole guide on this on another blog on our website, so have a look here. With all the components clean and free of road grime or mud then you stand a far better chance of completing the task effectively.
Second up, you are going to need some fresh fluid if you are going to do the job properly. Hydraulic fluid is hygroscopic which means it takes in moisture from the atmosphere over time. If your fluid has water within it then this will expand and evaporate when it gets very hot and cause your brakes to become spongy just at the moment you don’t need it to be. So buy a new bottle and you know you’ll be putting moisture free fluid into the system.
Dot 4 or Dot 5 though? Better check on the top of the reservoir – you don’t want to mix them …
Now this might sound obvious, but checking you’ve got the correct tools is pretty important. If your reservoir cap uses Torx fasteners rather than the usual phillips head screws, then you won’t get far if you don’t have a set of Torx in the toolbox!
Generally you are going to need an 8mm, 10mm or 11 mm on spanner to undo the bleed nipple on the caliper, a screwdriver / torx key to remove and refit the reservoir cap. You will also need a length of clear tube that fits snugly onto the top of the nipple and that is long enough to loop up at least six inches and then down into a suitable catch pot. Bungees or cable ties are often useful to hold the tube and the pot in place, and to hold the lever in when you are ready to tighten the nipple. Oh and some rags to mop up spillages and maybe a dust sheet / large cloth to protect your paintwork from spilled fluid when topping up the reservoir.
OK so we are ready to start. The bike on this occasion is our 2001 KTM EXC250 – we need to do a full bleed on this as we’ve removed the whole front master cylinder to replace the seal kit.
Put the bike on a stand and ensure you have good light to do the job. Ideally the handlebars should be straight to keep the reservoir horizontal. Remove the cap and the rubber expendable seal which should be fully pushed back for when it’s remounted later. If the heads on the screws on the cap are anything less than perfect then try to replace before you refit them – you don’t want them rounding off! To make the reservoir cap more accessible, you may need to move the throttle housing round and the hand guards down.
OK so now you are ready to start the process and to do so you are boing to have too loosen off the bleed nipple. As it’s fairly disastrous if the nipple rounds off or snaps, it’s worth spraying a bit of WD40 on it and leaving for a bit if you haven’t undone it for a while. It’s also definitely worth using a ring spanner rather than an open ender to initially loosen it off. Once done you can loosely tighten it again to fit the bleed tube. The tube should initially go up to encourage bubbles out of the system before arcing down to the catch pot.
So it’s time to start pumping through the fluid. The bleed nipple needs to be open when you are pulling the lever in and closed when you are releasing. It’s a tricky process to do on your own, so if you can rope in your significant other to help then all good, especially if you are bleeding from a totally empty system as we are.
You need to continue the process until flesh fluid has filled the whole system and is coming through without bubbles into the bleed tube. Keep an eye on the fluid level in the reservoir and top up as necessary throughout the process. Don’t let it run dry as you’ll have to go right back to the start. Once you are happy then pull the lever fully in and hold in place while you tighten the nipple. Gently release the lever and then pump again a few times to totally seat the pads. Your brake lever should now give the correct feel, and you can then adjust the bite point with the span adjuster / adjuster on the lever.
If all is good, then you can refit the expandable seal, being careful as fluid may spill at this point. Refit the cap and tighten the screws. You should put the spent fluid into a sealed bottle and take for recycling when convenient.
If you’ve followed all the above, then hopefully the brakes are working correctly. But what if they are not?
One of the most common reasons particularly on dirt bikes, is air remaining in the hydraulic hose in the section that curves upwards before going down to the caliper. You may need to turn the bars or take out the slack lower down the cable by pulling it and cable tieing it to ensure there is no high point in the cable. If there is, you will never get them bled!
Another reason could be air leakage from the banjo bolts at the top and bottom of the hose. This is unlikely if they have not been undone in the process, but very likely if you’ve removed components and reinstalled. In this case you really should have used fresh copper washers, so if you haven’t done that, then it’s a good move to do so before tightening to the correct torque. Oh and if your hoses are the problem, then it could be time to upgrade – Venhill are our ‘go-to’ cable supplier.
Once you’ve located the problem and corrected it, then return to the bleeding process and repeat.
So now you’ve done the front and if you’ve got enough time then it makes sense to do the back too on the basis that the fluid will be just as old. Bleeding the back is sometimes harder on a dirt bike as the reservoir if often very small and held on the top of the master cylinder. For this reason you need to keep an eye on the level very closely.
That said it’s a bit easier as you can sit alongside the bike and pump the pedal with the right hand and loosen and tighten the nipple with the left. On a road based bike the reservoir is often a remote unit held away from the master cylinder. It’s still usually a smaller volume unit so will need watching.
PAD AND PINS
The final part of the process should be to check the rest of the brake components. Remove the brake retaining pins and the brake pads and fully check them over for condition and the depth of pad left and replace as appropriate. If re-installing, then clean up the pads, remove and clean the anti-rattle clip and add copper grease if required.
For the brake pin, the surface should be smooth to allow the pads to remove freely as they wear. Light surface corrosion can be removed with fine emery paper, but if they are too bad, then replace. For the KTM they are £10.68 so nothing to break the bank!
Reinstall the components – you can put copper grease on the pins but it will be lost the first time you jetwash the bike! New R clips may be needed – we tend to cable tie them together to hold them secure in place.
So you are now done – brakes refreshed and working properly once again.
Now get out and ride!
PLEASE NOTE: THIS BLOG IS PRESENTED ONLY AS AN INDICATION OF HOW WE BLEED OUR BRAKES AND SHOULD NOT BE USED AS A DEFINITIVE GUIDE.
ONLY ATTEMPT ANY MAINTENANCE ON YOUR MOTORCYCLE IF YOU ARE COMPETENT TO DO SO AND HAVE SUFFICIENT KNOWLEDGE AND THE CORRECT TOOLS TO COMPLETE THE TASK SAFELY.
IF IN DOUBT, TAKE YOUR MOTORCYCLE TO A QUALIFIED MECHANIC.
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