Disc Brake Challenge Part V: Bleeding The Brakes And Bedding-In The Pads

Friday, August 21, 2009 by David Horvath
With the new brake pads and rotors installed, it's time for Samuel to bleed any air out of the brake lines. The first step is to check the condition of the brake fluid currently in the lines.

Step 1: Checking the fluid

Brake fluid is an interesting substance. It's actually a specialized type of hydraulic fluid and it does require inspection and or replacement over time.

You can't just top it off and forget about it. It should be checked regularly and flushed/replaced at least every 18-24 months depending on the condition of the fluid.

The brake fluid used in most automotive applications is hygroscopic. This simply means that over time, it will absorb moisture from its surroundings. It literally soaks up moisture from the atmosphere like a sponge.  The rubber brake lines on most cars and trucks can allow small amounts of moisture from the surrounding atmosphere to penetrate through their walls and into your brake fluid.

That can be extremely dangerous because of the high heat generated by the braking process. The fluid inside your calipers and wheel cylinders will be exposed to intense heat and any moisture trapped in the fluid can boil off forming gas bubbles inside your brake lines.

Any air or gas bubbles in your brake lines can compress and cause your brakes to fade or even fail to stop the vehicle under hard braking conditions.  

Checking your fluid is a simple matter of looking at it. Most normal brake fluid starts out as a clear liquid. As it absorbs moisture it will start to turn dark over time.

If your fluid looks like strong tea or coffee, it's time to change it ASAP.

Start by finding the brake master cylinder. It's typically located somewhere on the vehicle's firewall just behind the engine. 

The engineer that designed the location of the brake master cylinder on the 2002 Dodge Grand Caravan should be run out of town coated in tar and feathers. This has to be the worst location I have ever seen on a modern vehicle.  It's way up under the windshield cowl and you can barely access the filler cap.

master cylinder

The brake fluid reservoir sits on top of your master cylinder and it's translucent. That's so you can see the color of the fluid without actually opening the cap. If it looks like it's full of coffee or strong tea, it's time for a fluid change.

I sucked out some fluid using a clean syringe and hose to check the color. 

I did this part because brake fluid is a very caustic substance. You want to wear eye protection and you need to be careful not to let it drip. It will damage your car's paint and it will eat a hole in your clothes too! 

Our fluid didn't look all that bad. This is about what you would expect if the brakes haven't been looked at for a couple of years. This had ATE SL-6 fluid in it to begin with and it had a very light amber color to it. This is only a shade darker.

The fluid Samuel later drained from the lines was a different story.


STEP 2: Draining The Master Cylinder Reservoir



The next step was to suck out as much of the old fluid as possible from the master cylinder reservoir using the syringe and tube. Samuel dumped the old fluid into a clean gallon container that formally contained washer fluid.

All of the old fluid was taken to the local hazardous waste recycling facility and he clearly marked the bottle USED BRAKE FLUID.  

Then he topped off the reservoir with brand new ATE SL.6 brake fluid.

We have used this fluid before and it works well with the ABS brake system on the van. Even with the sticking caliper it held up very well to the excessive heat and abuse.

Samuel had to use a spare section of PVC drain pipe I had in my plumbing spares box to reach the filler neck.

Once again, my sincere thanks to whoever engineered the location of this reservoir! You can get a good idea of where it sits in this photo.  Jeesh! Obviously, ease of maintenance was the last thing on their mind when they decided to place this up under the windshield apron!!

filler neck


STEP 3: Bleeding The Brake Lines


Samuel then took our brake fluid bottle and a section of polyethylene hose and started to bleed the brakes while his sister sat in the van, pumping the brakes when prompted.

This led to some wonderful big brother, little sister banter as they attempted to synchronize their activities.

You want to use a clear or translucent hose and container so you can see the fluid as it is forced out of the brake bleeders. This is critical.

Following the instructions in the shop manual, he started with the rear passenger's side brake drum.

He worked his way from the bleeder furthest away from the master cylinder up to the driver's front caliper as he bled all four lines.

bleeding

You can see here how much darker the fluid was in the actual brake lines. It looked just like coffee!


The bleeding procedure is pretty much the same on all vehicles.

  • The first step is to remove the rubber covers from all four brake bleeders. These just pull off the nipple.


  • Clean down the bleeder valve and surrounding area with brake cleaner spray. This will help keep dirt or other contaminants out of your calipers and wheel cylinders.


  • You want to attach your hose to the brake bleeder nipple after you place a small wrench on the bleeder.


  • Next, have the person in the vehicle pump up the brakes until the pedal is firm and then hold the pedal down. This keeps the fluid pressurized in the lines.


  • Then, as they are holding the pedal down, the person bleeding the brakes gently turns the wrench to open the bleeder valve.  This forces the old fluid out  into the line and into your recycling container.


  • At first you will see very dark fluid and perhaps some air bubbles in the fluid. Some of the bubbles are from air moving through the threads of the loosened bleeder valve.  A drop of clean brake fluid on the threads will stop that and you may need to do that a few times during the bleeding process.


  • Once the pressure forces out the fluid and the flow stops, the person bleeding the brakes turns the bleeder valve shut and instructs the person in the vehicle to pump it up again.


  • The cycle repeats until you no longer see bubbles or dark fluid coming through the translucent tube.


  • You then move on to the next brake line until they are all flushed and filled with clean fluid.

Once the fluid was changed out, Samuel put the wheels back on and torqued the lug nuts to the recommended spec in the owner's manual.

Step 4: Burnishing/Bedding-in The New Pads:

We then took the van out for a test drive (with me driving of course) and we bedded in the Hawk HPS pads following the burnishing/bed-in instructions printed on the box.

The bedding-in process is extremely important with new brake pads. It allows the pad compound to properly mate with the rotor surface and when done properly, it creates a nice, even, transfer film of pad compound on the rotor surface. Here's a handy link explaining the importance of properly bedding in your brake pads:

Bedding-in Brake Pads and Rotors

Step 5: Letting The Brakes Rest


After performing the in ital bed-in procedure, it's important to let the brakes completely cool down. We parked the van and let it sit for a few hours before driving it again. Samuel was very happy and proud of himself. He was a bit uneasy when he started, but it went off with only a few hitches and the van's brakes work great now! Great job son! Now you can help me tackle the body work on my car!












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