Motocross Ruts Your Adrenaline Fix text
Mobile Navigation Button

How To Bleed the Brakes On A Dirt Bike


Coming up, we'll show you how to bleed the brakes on a dirt bike using only gravity and brake fluid, which is good to do periodically whether the brakes work adequately or not. Brake fluid is not supposed to last forever, and replacing old brake fluid can often provide additional stopping power, while reducing brake fade and improving the feel at the lever(s) while you're at it.

Whether you replaced a brake system component, or you merely opened the brake's hydraulic system, you'll need to bleed any trapped air from within the brake system, and gravity bleeding the brakes as we'll show you is something you can do by yourself, and is a very effective method of removing air from the brake system. Furthermore, as previously mentioned, bleeding the brakes as part of your routine maintenance, often results in performance benefits that include a firmer brake lever or pedal and shorter stopping distances.

Don't forget to keep the brake fluid clean & fresh as part of your motorcycle maintenance.

Safety First When Working On the Brakes

Working on the brakes does create a potential for loss of brakes and for this reason if you're uncomfortable working on the brakes, please do not attempt service of the brake system. Additionally, anytime you're working around brake fluid, be sure to always wear eye protection and adhere to the following points.

  • Cleanliness within the brake system is critical, and for this reason a brake flush or bleeding operation is best done after washing the dirt bike, as it's important to have a clean motorcycle before removing a master cylinder cover, or opening a bleeder.
  • A Dirt Bike's Front Master Cylinder Cover Showing the Proper Brake Fluid The brake fluid you use must be exactly what the manufacturer recommends, and coming from a new, previously unopened container.
  • On the original cover of the master cylinder reservoir, or in a service manual specific to the motorcycle you'll find the type of brake fluid to use, and it is critical that this is adhered to, otherwise seal damage could result, causing loss of braking abilities.
  • If you run out of brake fluid during a bleed, Never reuse brake fluid that has already been through the brake system, no matter how clean it appears.
  • Brake Fluid is Hygroscopic which means that brake fluid sitting in the reservoir, or in a previously opened container will absorb airborne moisture effectively ruining the brake fluid, therefore this is why it's recommended to periodically replace the brake fluid, and only replenish the brake fluid from a sealed container.
If you've ever disassembled a brake caliper or master cylinder and seen the build up that forms inside these components, this is corrosion of the aluminium parts that develops from moisture accumulation which forms due to brake fluid's hygroscopic characteristics.

How To Bleed A Dirt Bike's Front Brake

If you need replacement master cylinder cover screws and don't have time to wait for special order OEM screws, 4mm X 12mm countersunk phillips screws which fit most dirt bikes perfectly can be found at any major hardware store.
  • Before you embark upon bleeding the front brake you should ensure the front brake pads are in good condition, as pads which are worn beyond their wear limit can adversely affect the braking performance and transfer excessive heat into the brake fluid.
  • A Dirt Bike's Front Master Cylinder Reservoir Sight Glass Next, position the handlebars so the master cylinder is nearly level.
    Note: If the rider's lever positioning is extreme, it may be necessary to re-orientate the front master cylinder so the reservoir is level before removal of the reservoir cover, as this will prevent the fluid from running out of the reservoir upon removal of the cover, as well as will enable proper filling with fresh fluid by aligning the fluid level with the "High" mark.
  • Once the area is clean around the master cylinder, and the reservoir is somewhat level, remove the master cylinder cover screws, the cover and a diaphragm carefully so as to not allow any contaminants that may be trapped between the body of the master cylinder reservoir and the cover to fall into the reservoir's fluid supply upon removal of the cover.
Once the master cylinder cover is removed...
  • Using your finger, wipe the rim area of the master cylinder reservoir in a way that will direct any contaminants (Sand particles etc.) away from the fluid supply.
  • Next... If possible, use a vacuum source (A common syringe or baster works well for this if a vacuum pump is unavailable) then remove the fluid presently in the reservoir, being careful to not suck it dry uncovering the port(s) where the fluid supply to the master cylinder piston is located.
  • A Dirt Bike's Front Master Cylinder Reservoir Once the majority of the fluid is removed from the master cylinder reservoir, if the fluid has not been changed in some time, refill the reservoir again, then repeat the process of removing the fluid as a way of flushing the reservoir.
  • Now, fill the reservoir again with brake fluid so the fluid level in the reservoir is above the "Max" line and there is plenty of fluid available when starting the brake flush process.

Note: It is very important during this process that the brake fluid level in the reservoir does not get so low that the port in the bottom of the reservoir is uncovered, as this could allow air to be introduced into the brake system resulting in you being at this all day and into the night trying to restore adequate performance of the brakes.

Bleeding A Dirt Bike's Front Brake Caliper

Next, Using the proper size box end wrench (Most likely an 8mm or a 5/16" is equivalent) slip the box end over the brake bleeder on the brake caliper.

With the wrench in place, add a length of clear vinyl tubing to the bleeder nipple, then route the tubing into a suitable drain pan. (An empty water bottle works good, as these can be positioned in a way that you can monitor the amount of brake fluid that has been flushed through the brake system.)

Once you have the tubing attached to the bleeder, carefully open the bleeder about 1/4-1/2 of a turn watching for brake fluid to begin running out. (If you're having trouble loosening the bleeder, here's what to do if the bleeder is frozen.)

Do NOT Squeeze & Release the Brake Lever With the Bleeder Open.
If no brake fluid runs out of the bleeder, or you end up with no pressure at the lever with the bleeder closed, allowing the bike to sit overnight with brake fluid in the reservoir and the bleeder(s) closed often helps and will then make it easier to continue bleeding the brakes until optimum pressure is achieved.
  • Once the brake fluid is running through the line, grab a plastic hammer and gently tap on the caliper starting near the bottom and working your way towards the top, gently striking the caliper and directing the "Hits" in an upward direction, as doing this will force any air or old fluid that may be trapped in the area around the piston(s) to be dislodged and come to the top where it can exit through the bleeder.
    (If you don't have a plastic hammer, use the wooden handle of a hammer.)
  • Now continue this process until a generous amount of brake fluid has been flushed through the line while continually topping off the reservoir during this process.

Note: If no brake fluid exits from the brake bleeder within a few seconds of the bleeder being open, it may be necessary to remove the bleeder from the caliper, and using a stiff piece of wire or a pick, along with brake clean and compressed air, clear the orifice in the bleeder of any obstructions, then reinstall the bleeder in the caliper leaving it about 1/4th to 1/2 of a turn from bottomed so as to allow fluid passage, then continue with the brake flush or bleeding process.

  • Once a generous amount of brake fluid has run through the brake line and the reservoir is full, carefully monitor the reservoir level with the bleeder open, closing the bleeder when the level falls to between the "Min" and "Max" marks.
  • Now, with the bleeder closed tightly, carefully squeeze the front brake lever checking to be sure you have a firm lever.
  • If the lever squeezes to the handlebars, or is not as firm as you think it should be, continue to allow brake fluid to run out of the bleeder until all the trapped air is removed and adequate pressure is obtained.
  • With the brake fluid level at the proper height (Between the "Min" and "Max" marks), The bleeder tightly closed and a firm lever, ensure that the reservoir cover and gasket / diaphragm are clean by cleaning with brake clean followed by drying with compressed air, then reinstall the diaphragm, cover and screws.

Once you're done bleeding the brakes and everything is back together, it's a good idea to recheck the bleeder to ensure its tight, then rinse the area of the master cylinder and caliper with water, finally using compressed air to dry everything and clear the cavity in the bleeder of any water or brake fluid, then finish the job by installing a Honda bleeder cap over the bleeder to prevent any dirt or mud from being packed into the bleeder in the future.

Now, that's all there is to bleeding the front brakes in a way that'll leave you with a fresh feeling front brake that should be so powerful (provided that the front brake pads are in good shape) that throwing stoppies and out braking the competition should be a piece of cake now.

How To Bleed the Rear Brake On A Dirt Bike

Bleeding the Rear Brake Caliper On A Dirt Bike

If you've got a strong front brake and want to try to get the rear brake working a little better, bleeding the rear brake certainly can't hurt, as it's something that should be done periodically anyways, although if you've got a brake pedal that bottoms out without much stopping power it's important to ensure the rear brake pads are in good shape before doing anything.

Bleeding the rear brake is pretty much the same process as for bleeding the front brake, although there are a few other points to address which we'll be covering below, but regardless of which end you're working on, it's best to always ensure the motorcycle is clean before removing the master cylinder reservoir cap or loosening of a bleeder.

Most of the newer bikes have the rear brake master cylinder reservoir integral to the master cylinder itself, but there will always be a lot of dirt bikes which have a remote reservoir located above the master cylinder connected with a hose.

On the brake systems with a remote reservoir, it is possible to remove the reservoir from the feed hose for cleaning of the reservoir if desired before starting the brake bleeding operation and removal and cleaning of the reservoir should be performed if the inside of the reservoir appears dirty or stained.

Now, with everything around the immediate area of the reservoir and rear brake caliper clean let's get started.

  • On models which have the fluid reservoir integral to the master cylinder, begin by removing the reservoir cover screws, the cover and a diaphragm from the reservoir but do so in a careful manner so as to not allow anything such as small grains of dirt to fall into the reservoir.
On dirt bikes with a remote reservoir attached to the rear brake master cylinder via a hose, it's best to remove the seat, gas tank or subframe to gain unobstructed access to the reservoir, as this will also allow you to visually inspect seldom seen hoses, cables and wires for chaffing or other anomalies.
  • On models with a remote reservoir, once the reservoir is easily accessible, carefully remove the cap and the diaphragm while exercising care so as to not allow any dirt or other contaminants to fall into the fluid supply.

Once the Rear Brake Reservoir Cover is Removed...

  • Next, use your finger (without a rag) and wipe the rim area of the master cylinder reservoir in a way that will direct any contaminants (Dirt particles etc) away from the fluid supply before continuing.
  • Then... If possible, use a vacuum source (A common syringe or baster works well for this if a vacuum pump is unavailable) to remove the fluid presently in the reservoir.
    Note: If you are working on a dirt bike with an integral reservoir, be careful to not suck it dry uncovering the port(s) where the fluid supply to the master cylinder piston is located. If the system your working on has a remote reservoir, it is alright to remove all the fluid from the reservoir as the hose between the reservoir and master cylinder will still have fluid in it to supply the master cylinder with enough fluid as to not uncover the port(s) supplying the piston, allowing air to be introduced into the brake system.
  • Once the majority or all of the fluid is removed from the master cylinder reservoir (Depending on the type of reservoir) refill the reservoir again, repeating the process of removing the fluid as a way of flushing the reservoir before beginning the brake flush.
  • Once the reservoir has been flushed, fill the reservoir again with brake fluid, at this point it is best to fill the reservoir above the "Max" line so as to have plenty of fluid available when starting the brake bleeding process. This is especially true when working with a brake system that has an integral master cylinder reservoir as these have a much smaller capacity and can run dry quickly during the brake flush process easily allowing air to be introduced to the brake system.
Remember; It's Critical during the brake bleed process that you don't allow the fluid level to become so low in the reservoir that the port(s) in the bottom of the reservoir are uncovered on an integral master cylinder reservoir, as this could allow air to be introduced into the brake system resulting in inadequate performance of the brakes and requiring longer bleeding times.
  • Next, Using the proper size box end wrench (Most likely an 8mm or a 5/16" is equivalent) slip the box end over the brake bleeder on the brake caliper.
  • With the wrench in place, add a length of clear vinyl tubing to the bleeder nipple, then route the tubing into a suitable drain pan. (An empty water bottle works good, as these can be positioned in a way that you can monitor the amount of brake fluid that has been flushed through the brake system.)
  • Once you have the tubing attached to the bleeder, carefully open the bleeder about 1/4-1/2 of a turn watching for brake fluid to begin running out. (If you're having trouble loosening the bleeder, here's what to do if the bleeder is frozen.)
Do NOT Depress & Release the Brake Pedal With the Bleeder Open.
  • Once the brake fluid is running through the line, use a plastic hammer and gently tap on the caliper starting near the bottom and working your way towards the top, gently striking the caliper and directing the "Hits" in an upward and forward direction, as doing this will force any air or old fluid that may be trapped in the area around the piston(s) to be dislodged and come to the top where it can exit through the bleeder.
    (If you don't have a plastic hammer, use the wooden handle of a hammer.)
  • Now continue this process until a generous amount of brake fluid has been flushed through the line while continually topping off the reservoir during this process.

Note: If no brake fluid exits from the brake bleeder within a few seconds of the bleeder being open, it may be necessary to remove the bleeder from the caliper, and using a stiff piece of wire or a pick, along with brake clean and compressed air, clear the orifice in the bleeder of any obstructions, then reinstall the bleeder in the caliper leaving it about 1/4th to 1/2 of a turn from bottomed so as to allow fluid passage, then continue with the brake flush or bleeding process.

  • Once you've flushed a generous amount of brake fluid through the brake line and the reservoir is full, carefully monitor the reservoir level with the bleeder open then close the bleeder when the level falls to between the "Min" and "Max" marks.
  • Now, with the bleeder closed, depress the rear brake pedal checking to be sure you have a firm feeling pedal, If a firm feel to the pedal is not felt, continue to allow brake fluid to run through the system then close the bleeder and check for adequate pressure again.
  • With the brake fluid level at the proper height (Between the "Min" and "Max" marks) and a firm pedal, ensure that the reservoir cover and gasket / diaphragm are clean by cleaning with brake clean followed by drying with compressed air, then reinstall the diaphragm, cover and screws on the integral reservoir's or the diaphragm and cap on a remote reservoir.

Once everything is back together, it's a good idea to recheck the bleeder to ensure its tight then rinse the area of the master cylinder reservoir and caliper with water, finally using compressed air again to dry everything and clear the cavity in the bleeder of any water, then finish the job by installing a Honda bleeder cap over the bleeder to prevent any dirt or mud from being packed into the bleeder in the future.

That's all there is to bleeding the rear brake in a way that's sure to leave you with a rear brake that should be so powerful provided that the rear brake pads are in good shape, that brake slides will be easy and coupled with the front brake, brake checking the competition should become routine and this is especially true if your front brake is performing at it's peak.

Provided that the brake pads are in good shape at both ends, and you followed the steps above for servicing your front brake, embarrassing the competition by brake checking them should come naturally now.

What To Do When the Bleeder or Cover Screws Won't Loosen

What to do when the screws securing the master cylinder cover won't loosen

If you tried to loosen the screws securing the master cylinder cover and the screwdriver "slipped" leaving you feeling hopeless for getting the cover removed, (especially considering the way the screws look now) it's not all that bad and the tips below will illustrate how to remove the screws securing the cover to the master cylinder.

If you need new screws and can't wait for the OEM screws to come in on special order, 4x12mm countersunk phillips screws can be found at most major hardware stores and will fit most dirt bikes perfectly.

If the screws that are securing the master cylinder cover started to round out (which is to be expected) and you stopped before mangling them try this:

  • First, ensure there is no dirt or anything else packed into the bottom of the screw heads, If there is, get it out using a small pick, brake clean and compressed air, then grab a good phillips screwdriver and a hammer.
  • Next, place the screwdriver in the screw head, then while putting a slight turning pressure on the handle (but not enough pressure to cause it to slip again), use the hammer and lightly hit the top of the screwdriver while turning and see what happens.

If the screws are still not moving, check out this next tip.

What To Do When the Screw Heads are Ruined
If you're at a point where the screwdriver won't grip at all, use a small sharp chisel or a center punch with a good tip and a hammer to carefully turn the screws in a counter clockwise direction. If you do this carefully you should be able to get the screws loose without making the reservoir cover look hammered.

Once you have the old screws out, be sure that you replace these screws and when reinstalling them make sure you apply a very light coating of antiseize to the threads to help prevent any problems in the future.

What To Do If The Bleeder is Frozen & You Can't Get It Loose
If the brake bleeder won't budge, begin by using a brass hammer to strike the bleeder straight on hitting the bleeder at the top while turning.

When striking the bleeder you want to be hitting it downwards like driving a nail while attempting to turn the bleeder but do NOT hit it hard. Just use repeating taps as this will shock the threads, often allowing you to break the bleeder loose.

If you have a heat source you're thinking about firing up DON'T. Using heat should only be a last resort and even then you better start thinking about rebuilding the caliper or finding a new one. Applying heat to the caliper is likely to cause problems such as leaking seals which will leave you with no brakes, so firing up the torch isn't recommended.

Saving the best for last...
If you really want a strong front brake when you get to the first turn try this... Use a zip tie and tie the front brake lever to the handle bars leaving moderate pressure on the lever for about 30 minutes before a race, then cut the zip tie off and go to the line but be forewarned:
You might be surprised at the brake's performance when you get to the 1st turn!!




Wondering If We Cover More of Your Dirt Bike Interests?
Find Out Right Now.