Section 06-06: Brake System, Hydraulic | 1996 F-150, F-250, F-350, Bronco and F-Super Duty Workshop Manual |
WARNING: BRAKE FLUID CONTAINS POLYGLYCOL ETHERS AND POLYGLYCOLS. AVOID CONTACT WITH EYES. WASH HANDS THOROUGHLY AFTER HANDLING. IF BRAKE FLUID CONTACTS EYES, FLUSH EYES WITH RUNNING WATER FOR 15 MINUTES. GET MEDICAL ATTENTION IF IRRITATION PERSISTS. IF TAKEN INTERNALLY, DRINK WATER AND INDUCE VOMITING. GET MEDICAL ATTENTION IMMEDIATELY.
In a modern braking system, the driver of the vehicle provides force by pushing down on the brake pedal (2455). In power brake systems, this force is increased by a vacuum or hydraulic power brake booster (2005) and is applied to the brake master cylinder (2140). The force applied to the brake master cylinder pistons transmits pressure through the brake lines to each brake piston, resulting in braking action at each wheel (1007).
The system consists of the following:
The dual brake system is split front and rear with the front wheel brakes comprising one circuit and the rear wheel brakes, the other circuit.
Brake System, F-150, F-250, F-350 and Bronco, Typical
| Item | Part Number | Description |
|---|---|---|
| 1 | 2078 | Front Brake Hose |
| 2 | N802768 | Single Clip |
| 3 | 2264 | Front Brake Tube (RH) |
| 4 | 2263 | Front Brake Tube (LH) |
| 5 | 2264 | Front Brake Tube |
| 6 | N804645 | Clip |
| 7 | 2078 | Brake Tube |
| 8 | 2814 | Brake Hose Clip |
| 9 | 2C267 | Tee Assembly |
| 10 | 2B373 | Anti-Lock Brake Control Module |
| 11 | 383057 | Union |
| 12 | N802770 | Triple Clip |
| 13 | 2C190 | Rear Brake Anti-Lock Sensor |
| 14 | 2267 | Rear Brake Tube (RH) |
| 15 | 2267 | Rear Brake Tube (LH) |
| 16 | 2265 | Tube |
| 17 | N620398-S36 | Nut, Anti-Lock Brake Control Module-to-Frame |
| A | — | Nut. Tighten to 17-23 Nm (13-17 Lb-Ft) |
The ability of a brake system to stop the vehicle is dependent on the available traction.
Assuming there is traction, a brake system has to deal with other critical requirements. There must be a balance of the brake forces applied from side to side. If this were not the case, several things might happen. The vehicle might pull to one side or the wheels on one side might lock up prematurely, which could result in a skid.
Another important requirement is having the front and rear brake forces balanced. This allows all four wheels to utilize available traction and stop the vehicle in the shortest distance. Lightly loaded wheels may lose traction with less braking force than heavily loaded wheels.
For example, the black truck in the following illustration is carrying its maximum-rated load in the truck bed. For maximum brake performance, it needs more brake force directed to the rear, because the weight distribution gives the rear more traction. The white truck is empty in the rear and carrying a snow plow on the front. For maximum brake performance, it needs less braking power in the rear and more in the front. That is one of the reasons manufacturers provide gross axle weight ratings as well as gross vehicle weight ratings on each truck. There are limits to the loading and weight distribution that the truck is designed to accommodate. Exceeding these limits may adversely affect the brake performance.
Balanced Brakes
Besides assuring that the maximum brake force is directed where it is needed to provide shorter stopping distances, brake balance also assures that the wear on brake pads and linings will be reasonably equal under normal operating conditions. This makes the required brake system maintenance more predictable.
Brake Fluid
The general principles of hydraulics apply to any fluid in a closed system. But this doesn't mean that just any fluid can be used in a braking system. The fluid used in Ford vehicles is Ford High-Performance DOT 3 Brake Fluid C6AZ-19542-AA specially engineered to meet the unique requirements of the hydraulic braking system.
Use only brake fluid that meets or exceeds Ford specification ESA-M6C25-A.
Brake Fluid Boiling Point
One of the key aspects of brake fluid quality is the temperature at which it boils. A comparison of the boiling points for DOT 3 (in general), Ford DOT 3 and DOT 5 brake fluids is shown. If brake fluid boils in the brake system, it forms vapor which reduces the ability of the brake system to develop hydraulic line pressure. If brake fluid boils, the system acts just like a system with air in the lines, except that it reverts to normal operation when the brakes cool and the vapor condenses.
| F | C | |||
|---|---|---|---|---|
| Dry | Wet | Dry | Wet | |
| DOT 3 | 401° | 284° | 205° | 140° |
| DOT 5 | 500° | 356° | 260° | 180° |
| Ford DOT 3 | 550° Exceeds Requirements | 288° Exceeds Requirements | ||
Note: A newly opened can exceeds all minimum requirements.
Brake fluid absorbs moisture from the air and must be stored in the original container with the cap securely fastened. If not, its moisture content will increase and the boiling point will drop. Moisture also will be absorbed while the fluid is in the brake system, but a properly capped and sealed brake master cylinder reservoir will limit the rate at which this occurs.
DOT Differences
DOT 3 is the standard brake fluid in the U.S. for cars and light trucks. It is colorless. Note again that Ford DOT 3 brake fluid far exceeds minimum federal standards when new. This advantage continues with ordinary use and proper maintenance of the brake system. Any DOT 3 fluid will absorb moisture rapidly if its container is left open during storage or if damaged brake master cylinder reservoir seals allow large amounts of moisture to enter the brake system.
WARNING: DO NOT USE DOT 5 BRAKE FLUID IN A SYSTEM DESIGNED FOR DOT 3 BRAKE FLUID.
DOT 5 is a silicone-based fluid. It is purple in color. DOT 5 has good wet and dry boiling points. However, it is more compressible than DOT 3 and has been reported to give a "soft" pedal feel in operation. DOT 5 does not readily mix with DOT 3. There have been reports of damage to seals resulting when DOT 5 is mixed with or substituted for DOT 3 in a system designed for DOT 3.
Moisture entering a system with DOT 5 does not combine with the fluid as it does with DOT 3. A good comparison is gasoline with and without a moisture controlling additive. DOT 3 is like gasoline with an additive: the moisture blends with the fluid. DOT 5 behaves like gasoline without an additive. The moisture doesn't fully blend with the fluid. When enough moisture is present, pockets (or puddles) of water form. These pockets or puddles migrate to low points in the system, such as rear wheel cylinders (2261) and disc brake calipers (2B120). At high enough temperatures, this water will boil. At very low temperatures, it will freeze and form ice.
In summary, the drawbacks of DOT 5 are that it doesn't mix well with DOT 3 and it doesn't fully blend with water that may enter the system. As a result, it may require changing more frequently.
Ford High Performance DOT 3 brake fluid is the best brake fluid for all Ford vehicles built for the North American market (and many competitive vehicles as well). It is the only brake fluid approved for Ford warranty repairs.
Keeping Brake Fluid Cool
Along with being kept as dry as possible, the fluid in a vehicle's braking system must also be protected from excessive heat. Since braking generates heat, even the best of fluids may develop vapor pockets if the driver rides the brakes or the brakes drag due to poor maintenance.
When descending long, steep grades, drivers should downshift the transmission to assist in controlling vehicle speed and to reduce the load on the brake system. Overloading a vehicle or towing a trailer with inadequate trailer brakes may also cause excessive heat buildup.
Heat buildup in the engine compartment can adversely affect the braking system due to the following:
Heat buildup may also result when brake components and brake lines are too close to hot engine and exhaust components. If it is suspected that the brake fluid in a system is vaporizing, check for possible external heat sources. If the vehicle has been modified, certain areas or components may have to be shielded from these external heat sources.