Problem: Brake fluid contaminated with petroleum based fluid (i.e. power steering fluid, motor oil, transmission fluid)
Cause: Untrained person topped off master cylinder with fluid other than brake fluid. Brake rubber parts are not compatible with petroleum based fluids. Exposure to these fluids will cause the rubber parts to swell as shown in Figure 69.1.
Solution: If the foreign fluid has been in the system long enough the rubber diaphragm in the master cylinder cap will be distorted and gummy. The best test for petroleum based fluids is the water test. Use these steps to perform the water test:
1. Remove a small amount of the suspect fluid from the reservoir. It is best to pull the fluid from the top of the reservoir due to the fact petroleum based fluids are lighter than brake fluid.
DO NOT use the same drain tool used for normal brake jobs unless you clean it after use.
2. Place the suspect fluid in a clear container filled partially with water. If there is petroleum based fluid in the brake fluid it will separate and float to the top. If two layers form as shown in Figure 69.2 then you have a contaminated system.
Note: Some systems, especially GM, use a silicone based assembly lube in many of their brake parts. This silicone assembly fluid has a tendency to migrate to the fluid reservoir. It will appear as small droplets both on the surface of the brake fluid and the rubber diaphragm. DO NOT mistake this for petroleum based fluid. You can usually tell the difference by taking a small amount and smelling it and rubbing it between your fingers. It will have a different smell and feel from petroleum based fluids.
If the foreign fluid introduced was petroleum based the repair procedures are:
1. All components having rubber parts will have to be replaced or rebuilt. On a non-ABS equipped system this will include: master cylinder, brake valving, rubber hoses, calipers and wheel cylinders. If the vehicle is equipped with ABS the modulator will have to be replaced.
2. All steel brake lines will have to be flushed to remove any traces of the petroleum based fluid. using brake fluid to do this will NOT remove the contaminates. use either denatured alcohol or brake clean to perform the cleaning. Flush enough cleaner through each brake line to insure all contaminates are removed.
3. Bleed and flush the system with the correct fluid type. the fluid type can be found on the master cylinder cap.
Note: Some customers will request a partial repair when their system becomes contaminated. This should almost never be done. Brake fluid circulates through the system. Every stroke of the brake pedal takes brake fluid from the reservoir and brings it into the hydraulic system. Installing only a master cylinder will usually only result in a short term “fix” for the problem. it is very common for the new master cylinder to return with swelled rubber parts shortly after being installed. Remember simply flushing the system with new brake fluid will NOT remove the contaminates.
Tip: Always perform an underhood inspection as part of the brake inspection process. This will prevent unnecessary surprises like finding a contaminated system after the wheel based brake job has been performed.
To learn how to further test the effectiveness and safety of your brake fluid visit the link shown below. Once you have arrived at the website, click on the video featuring famous car enthusiast Stacey David to learn about brake fluid contamination and the proper measurements needed to know if your brake system is safe to operate.