How To Bleed Front Brakes


HOW TO BLEED FRONT BRAKES IN QUICK EASY STEPS

Brake fluid like suspension oil, is not on everyone’s top list of items to service due to the fact that it is a messy and time consuming job; not to mention that the consequences of making a pigs ear of it are a little too much for most people. We will start with a frame of reference to set the article up and give you some background information.

If you have ABS, your service manual will tell you exactly what steps you must take to service the braking system correctly, or if it needs to be done by the dealer as specialized equipment is needed. Don’t short cut this process and either do it right with the right tools or let the dealer do it!

Bleeding at the master cylinder

Bleeding at the master cylinder

BRAKE FLUID

You will find that on the top of each and every master cylinder it will specify what type of brake fluid to use:- DOT 3, 4 etc. Take this seriously and use exactly what the manufacturer states.

In so doing, also take the time to look at the different boiling points offered by brake fluid manufacturers in that category of fluid eg: DOT 4. The higher the boiling point the less fade you are going to get. Is this important for a commuting bike? Sure it is, as those brakes will be used all the time. For a sports tourer – maybe not so? Reflect on how you use your brakes:- how often and with what level of aggressiveness? Let those criteria determine the heat range of the brake fluid you use.

Another important point that often gets overlooked is that brake fluid is hydroscopic (it wants to attract moisture).  Over time therefore, brake fluid not only gets heat cycled to death, it also gets water in the fluid and that creates a lot of fade after a while as the water heats up far quicker than the brake fluid. Water in the brake fluid will also make the brake lever feel mushy when the brake fluid gets hot.

Does that help you understand why brake fluid needs to be changed VERY frequently? Your life may depend on it so take the time to do this often, at east every 4-6 months if you frequently use your bike. If it is a track or race bike, consider doing it every 4 track or race days.

One last note. If you have an open container of brake fluid in the garage, don’t use it unless it is less than 8 weeks since you first cracked the bottle open to use it. Therefore only buy the very small bottles, or change all the brake fluid in all your bikes at the same time.

Elevated speeds = elevated servicing intervals!

COMPONENTS

A brake reservoir can be a unit attached to the brake master cylinder by a hose, or it can be built in as part of the casting. In either case, you will see that there are a couple of screws holding the cap on or a retaining clip and screw keeping the cap in place. Once the cap is off, you will find in most cases a rubber gasket and a plastic ring or metal clip on top of the rubber seal.

Bleed nipples abound in most systems which really helps with the bleeding process. Normally they are covered with a small rubber cap that fits tightly over them. The cap ensures that dust and debris don’t pile up in the bleed nipple itself and can’t accidentally fall in to the calipers or brake system. That debris can block a return path, and that can be highly dangerous!

TOOLS:

You will need a fresh bottle of the correct DOT brake fluid, a hose that fits tightly over the bleed nipple (Some come with a one-way valve) , a bottle of sorts that the hose attaches into or on and the correct size combination wrench of 8,10, or 12mm. Make sure you compile everything you need before you start this job!

You can also go a little more high tech and by something like a Mighty Vac or Stockton Tool Company’s Brake Bleeder Deluxe that pulls the fluid through, or if you have a compressor get a vacuum attachment for it that does the same thing. This does not mean that you never manually bleed the brakes again – it just speeds up the process of old fluid out and new fluid in.

Take your wrench and try to loosen each bleed nipple. If it hasn’t move for a while, it may take a little force to get it to break free. It may take a lot more force than you think, and that in turn will put a lot of stress on the bleed nipple. Use the handlebars to position the front wheel in the direction you are turning the bleed nipple so you use the steering stops to your advantage! You only need to crack it open and then snug it back up. This is a very important step, so don’t bypass it.

Brake fluid can be recycled so make sure you recycle it!

TECHNIQUE

There are several schools of thought on how to bleed brakes, and we will combine a couple of them in this article. Let’s start at the top with the master cylinder reservoir.

Before you remove the cap, turn the bars to full left lock to position the reservoir upright making sure the fluid is as close to level as possible.

Carefully remove all components and put then on a clean rag.

NOTE: you don’t want to use rags or towels that will leave will leave lint residue on any of the components!

This will provide you with easy access to the fluid in the reservoir, so you can do one of two actions:

  1. Using a suction device, suck all the fluid out of the reservoir
  2. Soak up all the fluid with shop towels

Once the reservoir is completely empty, clean it out thoroughly of any old fluid by wiping only (DO NOT USE BRAKE CLEAN ETC)

Prep the entire area with paper towels that will absorb any spilt brake fluid quickly and be excessive with the amount of towels you use (much less expensive than repainting!).

Fill the reservoir with new fluid to ¾ full. If you have a bleed nipple on the master cylinder, attach the hose to it and support the bottle it is attached to somewhere below the master cylinder (you may need to use bungee cords etc).

Now – are you right or left handed? This is critical in using the wrench correctly. Line yourself up with the right handlebar and see what hand you will use for the wrench/bleed nipple open and close and for pumping the brake lever. Make that decision before you start!

Keep the handlebars at full left lock. Pull on the brake lever several times to generate pressure, but don’t try to pull it all the way to the bar. Take the wrench and crack the nipple open and fluid should escape into the tube. Before the brake lever hits the bar, snug the bleed nipple again to stop the flow of brake fluid. That will make sure you don’t suck the old fluid back it and worse, any debris packed into the bleed nipple. Repeat this step several times until the reservoir level is down to ¼, and then refill it to ¾ full. At this point, you are done with bleeding the master cylinder so remove the tube carefully and wipe up any remaining brake fluid quickly with brake clean or Simple Green on a rag. Reinstall the rubber cap.

Next you want to bleed the caliper that is furthest from the brake master cylinder and that is normally on the left fork leg. Sometimes this is almost impossible to do by yourself unless you have a vacuum tool, so you may need to recruit help at this point in the process. Labor will be divided into two tasks:

  1. One person pumps the brake lever following instructions from the second person
  2. The second person opens and closes the bleed nipple and directs the individual pumping the brake lever
Bleeding at the caliper

Bleeding at the caliper

It is a very simple level of communication but can become a complete disaster in coordination, so if this is your first time talk it through using the following protocol:

–       pump the brake lever to generate pressure “lever ready”

–       open and close the bleed nipple “nipple closed, pump brakes”

–       Lever ready

–       Nipple closed, pump brakes and so on

Brake lines can differ with internal diameter (rubber and braided) and length, so you may need to fill the reservoir two or 3 times for each caliper. It is critical that you don’t run out of fluid in the reservoir or you will be starting from scratch!

Once done with that caliper, carefully remove the tube and clean the nipple area with brake clean or simple green, and reinstall the rubber cap.  Inspect your storage bottle and empty if needed.

Move on to the right caliper and repeat the process and communication techniques. Use the same amount of fluid from the reservoir. Clean the nipple when done and reinstall the rubber cap. Examine the rotors, wheel and tire very carefully for any flecks of brake fluid and clean off immediately.

At this point the bleeding process is complete, so start at the top and check there’s no brake fluid anywhere and that your rubber caps are all in place. Be thorough and clean again to give yourself piece of mind.

You need to top off the reservoir at this point in time and you must have an air gap in the reservoir for fluid expansion (no air gap = potential front brake lock up and crash).

With a remote reservoir, it is easy to do and fill to just shy of the upper level mark. With a built in reservoir there’s usually a sight glass, so fill it to the point that there’s an air bubble visible at the top of the window.

Now you can reinstall the rubber gasket (make sure it is fully collapsed) and then all other components. Don’t over tighten the fitting screws! Thoroughly clean around the master cylinder area again.

Now at last, turn the bars into the middle of the steering lock and check for brake pressure on the lever. If you have stock rubber lines it should feel just a tad spongy, but if you have braided lines it should feel similar to hitting a wall where the lever just stops during the pull action at about 30% of the range.

Finally, remove the plethora of paper towels you have used and double check the master cylinder, brake lines, painted surfaces, forks and gauges for any flecks of brake fluid and clean thoroughly.

The Author:

Dave Moss is the Founder of Catalyst Reaction and Host of OnTheThrottle video programming specializing in technical analysis and how-to segments. He has been working with street, track, and race riders and motorcycle suspension and chassis geometry since 1995 and has become an internationally recognized authority in his field through his work with regard to testing and tuning. Dave is an avid rider and races with AFM in Northern California and is the 2011 450 Superbike Class Champion.

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