The Brake Bleeding/Maintenance FAQ

by Kristian #562:
Please read the Disclaimer before attempting any work in this FAQ.

23/11/01

If you are looking for information on how to CHANGE your Brake Pads, see the Brake Pad FAQ


For Other Brake Questions see the:

DISCLAIMER: My Father told me a long, long time ago, if you are buying a used vehicle, there's two things you need to make REALLY sure of; Brakes & Tyres. Changing the Brake Fluid is a simple job, but nevertheless should not be done someone who is not that confident with their mechanical abilities. I'd say that very little mechanical experience is OK if you are mechanically inclined. Having "No Brakes" is not much fun and is just plain dangerous. ed


Take great care with brake fluid. It will rot pretty much anything known to man, especially organic stuff like eyeballs and skin. Keep it off the paint and if you spill any wash it off with gallons of cold water. Think acid and you'll be safe enough. Andy #982


Why should I bleed my brakes ?:

 

Well there are several reasons:

  1. New Brake fluid is fairly incompressible. So when you squeeze your brake, the force in the piston at the Lever goes to the piston at the calliper with the fewest losses. Over time however, a couple of things happen. One is that air can get into the system, either by absorption directly into the brake fluid or more commonly by absorption of water, which contains air.

    Air is much more compressible than Brake Fluid. Think in terms of childhood games with a needle-less syringe filled with water. If you put your finger over the end and squeeze the plunger, it doesnít move at all, or not so youíd notice. With air in the syringe rather than water you can compress it a fair bit. Same happens when air gets absorbed into your brake fluid. Itís what makes your brakes feel mushy or squishy.

  2. The second thing that happens is that the brake fluid can absorb water. This water very often gets into the system as a result of condensation due to heat, from when the brakes or hoses get hot. Water can have dissolved oxygen in it, which when hot expands into small air-bubbles. Enough of these can also make the fluid more compressible. The water, if left in the system, can cause corrosion of the Cylinder, which is what eventually ruins your seals. When you bleed your brakes and the old fluid is brown, part of that is the corrosion.

  3. Water in the fluid will boil and change state from compressible gas to incompressible fluid during the brake application, the change in volume causing a change in brake force. Old brake fluid can cause a failure that is fast and dramatic. i.e. if they get hot from constant use down a hill, you can have a situation where you will have NO BRAKES. So change the fluid regularly.

  4. Basically, if you ever do anything that results in fluid coming out anywhere except the filler, you need to think about bleeding. The F classics are very easy to bleed. I don't know about the ABS bikes, they might take longer. If you take the lever off the master cylinder there is no need to bleed.

How often should I bleed my brakes ?

 

Dot. 4 Brake fluid (or any new brake fluid) comes in many colors but is clear of debris or dark opaque color. If the brake fluid in your sight glass on the Handlebar becomes a darkish brown, it's time to change your brake fluid. Good brake fluid is clear as a rule. Bad fluid can be clear, but tends to be cloudy. If it is clear the only way to test it is to measure the boiling point. This is not recommended at home, it is easier just to replace it at the set intervals.! If thereís two things you want to be absolutely sure of on your bike it's Tyres and Brakes. (and the Chain Master Clip, but that would be 3 things). Otherwise the BMW Manual recommends every two years. Many people do it annually, especially if they winterise their bikes.

How should I bleed my brakes ?

 

Bleeding your brakes involves replacing the old contaminated fluid with new fluid. Assuming you have the stock bleed nipples:

 

Note Well:

 

  1. Brake Fluid is like Paint Stripper. If you spill any on your paintwork it will eventually strip the paint. So don't drip any or spill any, if you can help it.!
  2. I hesitate to write this because I am afraid someone (children) might try it, but DON'T it's dangerous. If you have a Pool or Pool Chlorine lying around somewhere, DO NOT let Pool Chlorine and Brake Fluid Mix. The chemical reaction produces a LOT of heat and a wicked flame. In enclosed spaces it is particularly dangerous. This goes for using Glass Jars that MAY have had Chlorine in it or any Cleaners, like Washing Powder which contains Chlorine, that may have been placed in a Jar.
  3. Don't get any on your eyes and try to keep it off your skin.

 

Parts/Consumables:

 

Notes on Brake Fluid:

Tools:

 

 

Safety

 

Spilt brake fluid should be washed off using a low pressure stream of fresh water. If you get in on your hands, you want to run them under a cold tap for at least 10 minutes. Don't use soap until you've washed and dried them, the soap can contain Chlorine type stuff. Brake fluid in a cut stings like mad, so you need to try and get water in the hole to wash it out. Latex medical gloves give reasonable splash protection. I'd recommend use of safety glasses.

Getting to Work:

 

If you are replacing your Brake Pads at the SAME time, (see the Brake Pad Replacement FAQ) note that the NEW pads are thicker than the old ones, and hence push the Piston in the Brake Calliper back a bit. Thus, once installed the Brake Fluid Level in the reservoir will be HIGHER than with the old pads. SO do the Brake Pad Replacement First and then the Brake Bleeding. If your Brake Reservoir was full BEFORE you replace the pads then, try and remove some fluid with a Turkey Baster or something first, otherwise when you squeeze back the piston in the Calliper to get your new pads IN you will cause the reservoir to OVERFLOW.

 

Rear Brake:

 

1.)     Remove the Seat and Remove the Right Hand Side Panel (Two Allen Bolts)

2.)     Under the Coolant Reservoir Tank is the Rear Brake Reservoir. (The one in that picture is too full).

3.)     Before you start. Make sure your reservoir and reservoir cap is clean. If you get dirt into the lines its like letting air in, because, dirt is also compressible. Remove the Reservoir Cap and have your New Brake Fluid Bottle handy.

4.)     Locate the Rear Brake Bleed Nipple. Remove the Rubber Dust Cap.

5.)     Now put your ring spanner over the Nipple FIRST, then attach the Plastic Hose, pushing it firmly over the nipple. Put the other end of the hose in the Jar.

6.)     Get your helper ready at the brake pedal.

7.)     Now just cracking open the nut, simultaneously get your helper to SLOWLY depress the Brake Pedal, and ask them to tell you how far down it's going as they do it.

8.)     When it's almost all the way down, Nip the Brake Nipple closed. Do this before your helper lets the Brake Pedal come up, otherwise you will suck not only the old fluid, but also air, back into the system. Nip means just tighten till it seats, then gibe it a very small amount more.

9.)     Repeat this exercise #7-#8, until the Brake fluid level is on minimum, but do NOT let it get empty, or you will introduce Air into the System.

10.) Top up the Reservoir and repeat the Brake Depress/Nipple Nut Open/Close (#7-#8) sequence.

11.) Keep repeating the reservoir fill exercise until the Fluid that comes out of the hose looks like the clear fluid that you are putting in. It should be only 2 or 3 reservoir fills.

12.) When it runs clear, Torque the Brake Nipple closed, clean the Nipple, put on the rubber dust cap. Do NOT over-tighten the bleed nut. It is steel and the alloy in the Calliper much softer. I stripped one on my car 15 years ago and it was an expensive lesson.

13.) Top up the Reservoir to Max., replace the Reservoir Cap and Replace the Side Panel.

 

Front Brake:

 

1.)     The Front Brake Reservoir is on the Handlebar, next to the Throttle.

2.)     Before you start. Make sure your reservoir and reservoir cap is clean. If you get dirt into the lines its like letting air in, because, dirt is also compressible. Remove the Reservoir Cap and have your New Brake Fluid Bottle handy.

3.)     Undo the Screws on the Reservoir Cover and remove the cover. Inside is a Black Rubber Diaphragm with a Triangular bit hanging down underneath it. Remove this from the Reservoir.

4.)     Locate the Front Brake Bleed Nipple. (top of Photo). Remove the Rubber Dust Cap.

5.)     Now put your ring spanner over the Nipple FIRST, then attach the Plastic Hose, pushing it firmly over the nipple. Put the other end of the hose in the Jar.

6.)     Get your helper ready at the brake pedal.

7.)     Now just cracking open the nut, simultaneously get your helper to SLOWLY squeeze the Brake Lever, and ask them to tell you how much it is to almost fully pulled in.

8.)     When it's almost all the way in, Nip the Brake Nipple closed. Do this before your helper lets the Brake Lever out, otherwise you will suck not only the old fluid, but also air, back into the system.

9.)     Repeat this exercise #7-#8, until the Brake fluid level is on minimum, but do NOT let it get empty, or you will introduce Air into the System.

10.) Top up the Reservoir and repeat the Brake Depress/Nipple Nut Open/Close (#7-#8) sequence.

11.) Keep repeating the reservoir fill exercise until the Fluid that comes out of the hose looks like the clear fluid that you are putting in. It should be only 2 or 3 reservoir fills.

12.) When it runs clear, Torque the Bake Nipple closed, Clean the Nipple, put on the rubber cap. Do NOT over-tighten the bleed nut. It is steel and the alloy in the Calliper much softer. I stripped one on my car 15 years ago and it was an expensive lesson.

13.) Top up the Reservoir to Max., replace the Reservoir Cap Screw up the Two Screws. They do NOT need to be Mega-Tight. You will either strip the screws or the worse the Reservoir.

 

Wipe all surfaces clean. Test you have Working Brakes before you ride off.

 

If you have replaced your Brake Lines or done some work which resulted in Brake the reservoir emptying you might have to flush quite a few reservoirs-full of brake fluid through the system and pump the lever a bit to actually make the brake actuate at all. It might FEEL like nothing's happening for a while, i.e. like there is absolutely no resistance, but persist with the Bleed Nipple open and do NOT let the reservoir go empty.
 

Note: Bleeding Brakes FAQ Clarifications:

  1. When you open the Bleeder Nipple (or Speedbleeder)  and squeeze the brake lever/pedal to force fluid out, you do NOT need to have the cover and diaphragm on the master cylinder. i.e. you do not need to put the master cylinder cover back on before applying pressure as it is not a Pressurized Chamber. However, please SQUEEZE SLOWLY or the plunger will squirt brake fluid all over your PAINT!

  2. To bleed brakes I loop some clear hose up and over the mudguard and down into a bottle. This way you don't have to tighten the nipple up as there is always fluid in the hose and air can't get in. You might use a bit more fluid but I never use an opened bottle at a later date anyway. Rick, 01 F650GS, Qld-Australia.

Aftermarket Solutions (for Bleeding Brakes)
or (I don't have a wife/girlfriend/friend/son/daughter  to help me. Isn't there an easier way ?)

 

Yes, there are several Aftermarket Solutions:

Speedbleeders:

Vacuum Pump:

 

This device allows you to SUCK the old fluid out and the new fluid through, rather than having to PUSH it through with the pedal or the lever. It saves you having to have someone else squeeze the pedal or lever. It can be used in conjunction with the Speedbleeders to make the job simple and easy without having to contort yourself between the Nipple and the Handlebars or Brake Pedal.

 

See Web Bike World Article on Vacuum Pumps.

Reverse Bleed:

What if it is till Spongy AFTER Bleeding?

 

Loosen the bleed screw. Pull the lever to the bar and TIE it there. Tighten the bleed screw. Park the bike with the master cylinder as high as possible. Leave it over night. Problem solved. Flash 412 (CO).

 

Feedback

Is there anything else I should check on my Brake System while I'm at it ?

Yes:

  1. Check the Calliper Mounting Bolts (Front Only, the rear is mounted on the Axle.). Note if you DO undo these bolts for any reason, see the Brake Calliper Retaining Bolt Warning.
  2. Another thing to check is that the calliper pins are free. Our brakes are what's called floating callipers which means the calliper floats on a mount which keeps it cantered on the disk as the pads wear. This way the brakes require no adjustments throughout the life of the pads. If the calliper begins to bind on the pins, or the wheel or fork is put incorrectly, the calliper applies uneven pressure to the pads, lessening the brakes' effectiveness. All that is required is to loosen all the stuff on the bottom of the fork a little bit, as if removing the wheel. Sit on the bike and pump the fork up and down a time or two, then re-torque everything.

How to check it: The way to check for the whole calliper thing is: Put the bike on the centre stand. Somehow apply weight to the back wheel, easiest way is to have someone sit on the luggage rack, and spin the front tire once it's off the ground. If you have an off centre disk, it will bind at some point and if you listen to the brake you will hear the disk drag more at one point than the rest. (It's normal for the disk to drag a little, but a good spin should keep the wheel turning for 10-20 revolution at least). (From Unknown contributor).

  1. Grease the Plunger, under the rubber sock. (You need to Remove the Brake Lever to get this out.)
  2. Check the Brake Pedal Pulse FAQ
  3. Check the Brake Squeal FAQ.
  4. Check the Brake Light FAQ.

 

Empty Sight Glass?

Q. I look in my Sight Glass (on the Front Master Cylinder and it appears empty?) What's with that?

A. It's Probably just OVER Full, so you can't see it, but check for leaks anyway

 

Feedback:

What is the Rotor Wear Limit?

When the Brake discs measure <4.5mm or are warped or BADLY scored. Measure SEVERAL places around the disc.

Feedback:

Self-Bleeding Brakes ?

Q. My front brake was getting a little less crisp than I like it, so I was preparing to bleed the system. Like y'do. Before I started, I squeezed the brake hard, to see if I could bring the lever in to reach the handlebar, which I couldn't. but the squishy sensation has gone. ok, ok, I am aware that you can 'pump up' a brake system by repeated presses but this was just ONE HARD PULL on the lever, with the ignition and therefore the ABS on. Why has the brake stayed crisp and sharp for a week now without having to repeat the hard press? Adamx#1001. Any ideas?

A. Moisture/water in brake fluid + some inspired riding? Haakon #626

1. What Haakon said.
2. a small bubble that finally floated up past the piston into the reservoir.
3. a small piece of rust or crud stuck in the piston seal/cup.
4. an early indication that your bore is rusted, or
5. your piston seal/cup is worn and close to failure. Especially likely if your master cylinder is older, and you bleed the brakes by over pumping the lever instead of pressure or vacuum bleeding. Todd #389.
 

When should I replace the Master Cylinder Boots?
by Raymo #1173 Chicago '01GS

The service manual indicates that the front & rear master cylinder primary sealing boots should be replaced every 24K miles for ABS bikes.

Rear Brake Free Play Adjustment?

 

Q. Can you adjust the rear brake pedal freeplay? I have to push the pedal over an inch before the brakes start engaging. It seems that the plunger is on a threaded rod with a nut, but I can't figger out how to adjust it so that there's less play.

A. Loosen the locknut. Turn the rod. It will go in/out depending on which way you turn it. Get it where you want it and then tighten the locknut. Flash #412