Monday, August 24, 2009

Maintenance - Brake system flushing

A maintenance item that has not been discussed for a long time is brake fluid flushing.

Every two or three years, it is a good idea to flush the brake system, removing the old brake fluid, along with dirt, debris and absorbed water. Brake fluid is hydrosorbic, meaning it absorbs water from the atmosphere. The absorbed water causes all sorts of problems, including rust. When the brakes become very hot, as when descending long downgrades, water in the fluid can boil leading to brake fade and/or brake failure. Another good reason to use low gears when heading downhill.

Brake fluid flushing is a chore that a qualified home mechanic can do. It requires only a handful of simple tools. Brakes are a critical safety system, so do this only if you have the proper experience to do it correctly. Even if you are not qualified, it is a periodic maintenance item that every MH owner should have done.

There are several ways of flushing or bleeding a brake system. Shops usually use a power flusher, which speeds the process. I use this method on our Jeep and Acura.

Not having the right adaptor for the LD, I use the gravity method, a simple, effective method whose major disadvantage it that it's slow. It takes a couple of hours to do but it can save you a lot of money. The flushing process basically removes the old dirty fluid and replaces it with clean fluid, while also removing any air that may be in the system.

Start by removing as much of the old fluid from the mater cylinder's reservoir. I used a rubber battery filler bulb. They cost less than $10. When done, flush the bulb out with water to preserve it.


After sucking out as much fluid as possible, flush the reservoir a couple of times with a few ounces of fresh fluid and suck it out. Then refill the reservoir to the top with fresh fluid. Check the owner's manual in your LD for the proper fluid. Our 2003 Ford E450 calls for DOT 3 fluid. I use Castrol GTLMA DOT3 because it is less susceptible to absorbing moisture and it has a higher boiling point, making it more resistant to brake fade.

Deposit the old fluid in a container for recycling at your local auto parts store or local Haz-Mat disposal site. I use old windshield washer fluid bottles for the dirty fluid.


The brake lines are flushed one brake caliper at a time, starting with the passenger side rear brake, proceeding to the driver side rear brake, then to the passenger side front brake and finishing with the driver side front brake.

Each brake caliper has a bleeder valve, covered with a rubber cap. Remove the bleeder's rubber caps before flushing and replace afterwards.

Ours LD bleeders have a 3/8" hex head. A 3/8" wrench or socket is used to loosen and tighten the bleeders.

After loosening the bleeder 2 or 3 full rotations, attach a clear plastic hose to the bleeder, with the other end of the hose dropped into a container to capture the old fluid. The clear plastic hose enables you to observe the color of the brake fluid as it drains. You will know when the fluid is flushed when the color of the fluid changes from a dark, dirty color to clear. When the fluid runs clean, remove the hose, tighten the bleeder valve and move to the next brake.

The fluid will slowly drain out. The passenger rear brake took almost 45 minutes before the old fluid ran clear, indicating that the old fluid was gone. The driver side rear brake only took about 15 minutes before it ran clear. After flushing the rear brake, move to the front brakes and repeat the process.

While the brakes are draining, frequently check and refill the master cylinder, making sure the reservoir never runs dry.

After the flushing is complete, make sure the bleeders are tight, the rubber caps replaced, the master cylinder fluid is topped off and its cap replaced. When finished, start the engine and push hard on the brake pedal, making sure it does not sink (which would indicate a leak).

Look at all the bleeders to make sure there is no leakage.Afterwards, hose off with water any brake fluid that has spilled since it will remove any paint it touches if allowed to remain.

Our 2003 23.5' LD required about 2-1/2 quarts of fluid to fully flush the system.

Brake flush photos.


After flushing, you should drive on a gravel road and hit the brakes hard several times to fire off the ABS system. This helps flush out the old brake fluid that is contained in the ABS pump and valves.

This fluid normally is not removed during a flushing unless a special electronic tool is used to open the ABS valves. Unfortunately, the old fluid is not removed from the system but it is diluted with the newly replaced fluid.

Ford or a good brake shop should have the tool and be able to fully flush the system.

Contributor: Larry Wade

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