Toyota 4Runner Topsites

Brake System Flushing




Did you know that you should regularly flush your brake fluid?  Most people don’t and here is why you should do it, regularly. 

Brake fluid is hygroscopic.  That means it loves to absorb water like a sponge and likes it so much it will suck water right out of the air.  As it absorbs water two bad things happen.  First is that it causes the boiling point of the fluid to go down reducing braking performance, and second, the moister causes the brake fluid to become corrosive and can damage brake system parts, very expensive brake system parts. 

The brakes generate lots of heat and the fluid in the brakes can get very hot.  If it gets hot enough it can boil, and when it does it goes from a liquid to a gas.  Remember back in school you leaned that fluids don’t compress well?  That is the whole concept behind hydraulic brake systems.  The brake fluid does not compress so it passes energy from the master cylinder that is connected to the brake pedal to the wheel cylinders, or calipers where the pads press against the rotors or drums to stop your car.  This all works well as long as the brake fluid remains a liquid.  If it gets to hot it will boil and transform its self from a liquid to a gas.  Remember air is a gas and you can really compress it, a lot.  You can take a lot of gas and compress it and put it in to a small place like a scuba tank.  The bad thing is that it will not transfer energy to the brake pads like liquid brake fluid can.   

Once your brake fluid boils, your brake pedal can go right to the floor and have little to NO affect on getting the brakes to stop the car.  This has happened to me several times in my work cars, but NEVER in any of my personal cars. 

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 DOT Types and Boiling Points:

DOT 3 brake fluid has a minimum boiling point of 400 degrees Fahrenheit.  DOT 4 has a minimum boil of 450 Degrees.   DOT 5 and 5.1 has a minimum boiling point of 500 degrees Fahrenheit, but they are not compatible with normal brake systems and are used in special racecar brake systems.  DOT 5 is a silicone fluid and will foam in ABS systems and you will have no brakes.  DOT 5.1 is non-silicone, but neither one is compatible with the Toyota brake system so forget about it.   

If your system is labeled for DOT 3 you can use DOT 3 or 4 and they can be mixed if needed.  I use DOT 4 in my vehicles.

The minimum boiling point ratings are as the fluid sits in its factory sealed container.  As soon as you open the container it starts to absorb moisture and the boiling point starts to drop.  When you add brake fluid always make sure you do so from a factory sealed container.

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As brake fluid absorbs moisture it can become corrosive and damage very expensive brake system parts like a $1400 ABS modulator pump.  A few dollars spent regularly flushing you brake system can save you thousands down the road especially in modern brake systems with all kinds of fancy stuff like ABS, Traction Control, Vehicle Skid Control, and so on.  Your brake system should be flushed yearly, but never longer then every two years.

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 Flush your brakes:

Brake fluid absorbs water from the atmosphere, lowering its boiling point and causing corrosion, particulate contamination, microscopic particles of rust and rubber accelerating the wear of very expensive brake components. This is why you should fully flush your brake system every year, but never more then every two years.  In addition, whenever the hydraulic system has been opened like when a component is replaced, the system must be bled of air. 

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 Flushing Methods: 

The brake pedal method:   

This can be done with two people or one with a “one man bleeding kit”.  The one man bleeding kit has a check valve that you attach to the wheel cylinder so air does not get drawn back into the system.   

Everyone knows about this method, but few know how bad it can be.  Normally the piston, which is connected to the brake pedal, only travels so far in the master cylinder.  When using the brake pedal flushing method, the piston can travel much further down in the master cylinder and contact an area that has never been touched by the piston or its sealing O-ring.  If the area has corrosion in it you can ruin the O-ring in just one pass and then you will need a new master cylinder.  This is most likely going to occur in a vehicle where brake flushing has not been done as often as it should have been.  If it has been neglected then you should only have it power flushed. 

Knowing that and you want to proceed you should check the shop manual and make sure that your brakes can be flushed this way.  Some GM cars cannot and they can only be flushed with a special computer that interfaces with the ABS system.  I can tell you that my 96 4Runner can be flushed this way. 

Determine how far down the brake pedal normally goes and put a block of wood under it to prevent it from going further down to prevent O-ring damage.  Next using a NEW turkey baster, not a used one so you do not contaminate the brake fluid and system.  Our use my favorite, a large sterile medical syringe.  Clean the outside of the master cylinder and reservoir to make sure no dirt can get into the brake system.  Remove the cap and use the turkey baster to remove as much of the old fluid as you can and top it off with new fluid from a factory sealed container.  Then go to the wheel cylinder that is furthest from the master cylinder.  On most cars that will be the right rear wheel, on the 3rd generation 4Runner with ABS it will be the left rear wheel.  Apply a 10mm box end wrench to the bleeder valve and a clear tube that goes into a collection container and you are ready to start. 

Tell your helper to apply pressure to the brake pedal while you open the bleeder valve.  Have your helper tell you when the pedal is against the block of wood and hold it there until you close the valve.  Let him know to let the pedal up.  It is important that he allows it to come all the way up for a few seconds while the master cylinder refills.  Keep going until you see nice new clear fluid free of bubbles coming out of the bleeder valve.  Stop and move to the next closest wheel to the master cylinder and so on until you get them all.  It is very important that you never let the level in the master cylinder reservoir drop below the MIN mark or you may get air into the system and have to start all over again.  Once you complete the last wheel, top off the reservoir and go for a careful test drive.  If the brakes are mushy that means you got air into the system and have to do it again until you get it all out.  Now you are done until next year. 

Here is another nifty idea.  There is a company called Speed Bleeder that sells a replacement bleeder valve that has a check valve built right in.  It looks like it would speed up the bleeding process especially if you had to do it by yourself.  The only thing is that for the speed bleeder to work properly the threads would have to remain air tight so the valves would have to be removed from time to time to apply more thread sealant.

Reverse Injection: 

There is some new equipment out that is for reverse injection of brake fluid.  The idea here is that you force new fluid into the wheel cylinders through the bleeder valve and flush the old fluid back out the master cylinder.   

I have one of these systems and flat do not like it.  I just do not think I can get the bleeder valve clean enough so I do not force dirt into the brake system.  I also feel that the fluid in the wheel cylinders is where it gets the hottest and maybe in the worst shape and I sure do not want to force the worst, dirtiest brake fluid backwards through the ABS modulator pump and the rest of the brake system. 

I may just be old fashioned here, but I just do not think this is a good idea. 

The reverse injector system can also be used to apply suction to the bleeder valve and such the old fluid out the bleeder valve.  I have tried this several time and I keep getting air sucked in past the threads of the bleeder valve into the wheel cylinder and it appears to me that I can not get all the air out of the wheel cylinder.  Overall the only thing I like about my reverse injection kit is the nifty collection bottle that I use when power flushing the brake system. 

Power Flushing: 

Power flushing is the ticket for flushing the brake system and you do not have to worry about damage to the master cylinder like in the brake pedal method. 

The professional power flushing systems have a big aluminum gadget that looks like a beer keg.  It has two chambers in it that is separated by a diaphragm.  One side of the diaphragm is the new brake fluid and the other is compressed air.  A hose is clamped on to the opening of the master cylinder reservoir to supply the reservoir with fresh fluid.  The tank is hooked up to the shops compressed air line and puts about 15 PSI on the diaphragm which forces the new fluid into the master cylinder reservoir and keeps it under positive pressure.  Then all your have to do is go around to the different wheel cylinders and allow the fluid to flow out until you see nice new fluid coming out of the bleeder valve.  This works really well, but the equipment is expensive and you need shop air to drive it. 

I just found a power flusher tank that works really well for the do it yourselfers.   

I got one from Motive Products and it sells for $49.95 for model PBU101. 

It works the very same way as the professional power flushing systems, just on a smaller scale.  You connect the hose with the universal adapter to the opening of the master cylinder reservoir and dump two quarts of new fluid into the tank and pump it up to 15 PSI and then run around and bleed it out of the wheel cylinders.  I was able to flush the brake systems in all three of my vehicles in about an hour and a half.  It is fast and really easy to use.  For the money it is a must have item.  Many shops charge well over $100 to flush a brake system.  You can get one of these tanks and do it yourself for $49.95 for the tanks and $20 in new fluid.  From then on all you need is the fluid.

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