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Problem: Low, spongy brake pedal

Cause: Air trapped in hydraulic system

Solution: RFI is a patented process from Phoenix Systems. The Phoenix Injector has been designed to perform RFI as well as pressure and vacuum bleeding. To perform RFI follow the steps below:

1. to perform RFI bleeding, first drain and clean the master cylinder reservoir. If necessary fill the before draining so an accurate measure of fluid can be taken. Note the amount of fluid removed. This will be necessary to avoid overfilling the master cylinder during the RFI bleeding process. In order to give the air an easy path out of the master cylinder raise the rear of the vehicle to allow the master cylinder to sit higher at the primary end (firewall) then at the secondary end. This will allow the air to exit the vent ports.

2. Remember caution is to be used when raising the vehicle to avoid an unsafe condition or vehicle damage. If the master cylinder cannot be positioned in this manner, get it to at least a point where the body is level. If this is not practical then remove the master cylinder from the vacuum booster and gently flex the brake lines to position the secondary end of the master cylinder (bumper end) lower than the primary side (firewall end). This will position the vent ports at the highest point.

3. Configure the Phoenix Injector for RFI bleeding as per the instruction manual. Follow instructions for priming the injector and lines. Once the master cylinder has been positioned then begin the bleeding process at the first wheel in the bleeding sequence. Connect the injection side of the tool to the bleeder and the vacuum side to the fluid supply container making sure it is full.

4. With the tool connected, open the bleeder screw and the slowly stroke the handle. Continue this at the wheel giving at least three to four strokes.

5. Once complete, remove the adapter from the bleeder and let the wheel cylinder or caliper burp or gravity bleed. Close the bleeder.

6. Repeat this process at each of the wheels remembering to watch the amount of fluid being used. It may be necessary to drain the reservoir during the process to avoid overfilling it. At the end of each wheel bleed remember to allow the caliper or wheel cylinder to gravity bleed.

7. Once complete check and adjust the master cylinder fluid level and test the pedal. If firm, test drive.

CAUTION: Never drive a vehicle with an unsafe pedal.


More Info: All bleed procedures published in service manuals are based on conventional bleeding techniques. Whether they work or not and how quick will depend on where the air is. In addition to these there is another relatively new technique available. It is called RFI, which stands for Reverse Fluid Injection.

This technique involves forcing fluid into the bleeder screws to force the fluid and air up to the master cylinder (See Figure 76.1).
Air naturally wants to travel up so this technique takes advantage of this. Most people who have never heard of this before are alarmed
because fluid is being pushed up stream. They are concerned about damaging the various hydraulic components. Two points to take into consideration this technique is used only as a secondary bleed technique. The fluid has already been flushed. Second it is done at very low pressures, usually less than 10psi. This prevents forcing any debris upstream. It can use effectively on most vehicles equipped with both ABS and conventional brakes.

screen-shot-2016-09-12-at-10-11-32-am Figure 76.1

RFI relies on the fact that the vent port is the highest point in the system. The fluid path is from the bleeder screw, through the lines, hoses and valves into the pressure chamber of the master cylinder. From there it escapes into the reservoir through the vent port (See Figure 76.1). This is providing the vent port is the highest point in the master cylinder. If the master cylinder is mounted level then the air will escape through the vent port. If it is mounted at an angle then it will be trapped in the end of the master cylinder. To use RFI bleeding on this style of vehicle the master would have to be brought to a level position. Either raise the rear of the vehicle until the master is level
or remove the master cylinder from the vacuum booster and rest it on the booster studs. When raising the vehicle be careful to do it in a safe manner. Some masters are mounted at too severe an angle to allow the use of this method. On these remove the master from the booster.
You might be asking yourself is all this worth while? I think you should first consider that you won’t have to do these extra steps on most vehicles. Next think back to the last time you or somebody else in the shop spent too much time bleeding a vehicle out. S
pending the extra 10 minutes to undo the master cylinder would have been time well spent. I speak from experience when I say that RFI is the most effective method to get a pedal back on a vehicle when used properly. With one exception.

RFI Exceptions: There is only one case where I am aware of where RFI will not work. It involves a unique style master cylinder. Master cylinders are supposed to have vent ports right? Well that’s what I thought too until about 5 years ago. TEVES makes a master cylinder that does not use vent ports. It uses valves in the center of each piston to control venting (See Figure 76.2). RFI will not work on this style of master cylinder because the air forced back to the master cylinder will be trapped above the check valves. These master cylinders seem to be used only on vehicles equipped with the TEVES IV ABS system. The reason for the elimination of the vent ports was to prevent damage to the cup seals during ABS operation. These master cylinders can be identified by looking for the large tube the connects the reservoir to the ABS modulator. The good news if that most of the time these systems do not prove too difficult to bleed.

screen-shot-2016-09-12-at-10-23-49-am Figure 76.2


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