Halderman ch096 lecture

Automotive Technology, Fourth EditionJames Halderman

BRAKE FLUID AND LINES

96 BRAKE FLUID AND LINES

ObjectivesObjectives• The student should be able to:

– Prepare for the Brakes (A5) ASE certification test.

– List the types of brake fluids. – Describe where armored brake line is used. – Discuss the differences between double-

flare and ISO flare.– Explain how flexible brake lines should be

handled during service.

ObjectivesObjectives• The student should be able to:

– List the precautions necessary when handling or disposing of brake fluid.

– Discuss the types of rubber that are used in brake system components.

BRAKE FLUIDBRAKE FLUID

Brake FluidBrake Fluid• Brake fluid is designed to function in

the hydraulic brake system under all operating conditions

• Boiling point is one of the most critical aspects and ratings for brake fluid

• Brake fluid should be changed regularly as part of normal routine service

Brake FluidBrake Fluid• All brake fluids must be able to pass

tests for the following:1. Fluidity at low temperatures.2. Controlled percentage loss due to

evaporation at high temperatures (tested at 212°F [100°C]).

tests for the following:3. Compatibility with other brake fluids.4. Resistance to oxidation.

tests for the following:5. Specific effects on rubber, including:

a. No disintegration

b. No increase in hardness of the rubber tested

c. Limited amount of decrease in hardness of the rubber

Brake FluidBrake Fluid• Physical Properties

– Brake fluid is a polyalkylene–glycol–ether mixture called polyglycol

– Polyglycol brake fluid is clear to amber in color

– Brake fluid has to have the following characteristics:

• A high boiling point

• A low freezing point

• Ability to not damage rubber parts in the brake system

Brake FluidBrake Fluid• Brake Fluid Specifications

– All brake fluid must meet Federal Motor Vehicle Safety Standard (FMVSS) 116

– The SAE the DOT have established brake fluid specification standards as shown in the following chart

DOT Brake Fluid SpecificationsDOT Brake Fluid Specifications

Brake FluidBrake Fluid• The wet boiling point is often called

“equilibrium reflux boiling point” (ERBP)• ERBP refers to the method in the

specification (SAE J1703) by which the fluid is exposed to moisture and tested

– DOT 3• DOT 3 brake fluid is the type most often

– DOT 3• DOT 3 brake fluid has some important

characteristics including:1. It absorbs moisture.

According to the Society of Automotive Engineers (SAE), DOT 3 can absorb 2% of its volume in water per year.

characteristics including:2. DOT 3 must be used from a

sealed (capped) container. If left open for any length of time, DOT 3 will absorb moisture from the surrounding air, which is called hygroscopic.

characteristics including:3. Always check the brake

fluid recommendations on the top of the master cylinders of imported vehicles before adding DOT 3.

– CAUTION: DOT 3 brake fluid is a very strong solvent and can remove paint! Care is required when working with DOT 3 brake fluid to avoid contact with the vehicle’s painted surfaces. It also takes the color out of leather shoes.

Figure 96-1 Brake fluid can absorb moisture from the air even through plastic, so many experts recommend that brake fluid be purchased in metal containers, if possible.

Figure 96-2 Brake fluid absorbs moisture from the air at the rate of about 2% per year. As the brake fluid absorbs water, its boiling temperature decreases.

– DOT 4• DOT 4 brake fluid is formulated for use by all

vehicles, that are designed to use DOT 3.

– DOT 4• DOT 4 is polyglycol based with added borate

esters to provide an extra buffer for the fluid against acids that can form in the moisture that has been absorbed in the fluid when it is heated.

– DOT 4• Some vehicle manufacturers recommend

that DOT 3 and DOT 4 not be mixed.

– DOT 4• If DOT 4 is to be used, the system should be

purged of all of the old DOT 3 and replaced with DOT 4.

– NOTE: Because brake fluid absorbs moisture over time, many vehicle manufacturers recommend changing the brake fluid as part of the standard services to be performed routinely. The typical recommended brake fluid change interval is every two years or every 30,000 miles (48,000 km), whichever comes first.

– NOTE: This is particularly important for vehicles equipped with an antilock braking system (ABS) because of the problem of expensive brake component wear or corrosion caused by contaminated brake fluid.

– DOT 5.1• DOT 5.1 brake fluid is a non-silicone-based

polyglycol fluid and is clear to amber in color.

– DOT 5.1• DOT 5.1 can be mixed with either DOT 3 or

DOT 4 according to brake fluid manufacturers’ recommendations.

– CAUTION: Some vehicle manufacturers such as Chrysler do not recommend the use of or the mixing of other types of polyglycol brake fluid and specify the use of DOT 3 brake fluid only. Always follow the vehicle manufacturer’s recommendation.

– DOT 5• DOT 5 brake fluid, commonly called silicone

brake fluid, is made from polydimethylsiloxanes.

– DOT 5• DOT 5 brake fluid is purple (violet) in color.

– DOT 5• It is called nonhygroscopic because it does

not absorb any water.

– DOT 5• DOT 5 is tested using standardized SAE

procedures in a humidity chamber.

– DOT 5• Silicones have about three times the amount

of dissolved air as glycol fluids, which causes concern about its use

1. Silicone brake fluid has an affinity for air; therefore, it is more difficult to bleed the hydraulic system of trapped air.

2. The trapped air expands with increasing temperature, causing the brake pedal to feel “mushy.”

3. The air trapped in the silicone brake fluid can also “off-gas” at high altitudes, causing a mushy brake pedal and reduced braking performance.

4. DOT 5 brake fluid should not be mixed with any other type of brake fluid. Therefore, the entire braking system must be completely flushed and refilled with DOT 5.

5. DOT 5 does not affect rubber parts and will not cause corrosion.

6. DOT 5 is expensive. It is approximately four times the cost of DOT 3 brake fluid.

– NOTE: The characteristic of DOT 5 silicone brake fluid to absorb air is one of the major reasons why it is not recommended for use with an antilock braking system (ABS). In an ABS, valves and pumps are used which can aerate the brake fluid. Brake fluid filled with air bubbles cannot properly lubricate the ABS components and will cause a low, soft brake pedal.

Figure 96-3 DOT 5 brake fluid is used mostly in motorcycles because if spilled, it will not hurt painted surfaces.

Brake FluidBrake Fluid• Brake Fluid Inspection and Testing

– The brake fluid should be inspected regularly, including the following items:

• Proper level: Brake fluid level should be above the minimum level (labeled MIN) and below the maximum (labeled MAX) on the side of the master cylinder reservoir.

• Color/condition: New brake fluid is clear or amber in color. Discolored fluid should be changed.

• Tested using a tester or test strips: Test strips can be used to measure copper ions that increase as the brake fluid becomes deteriorated.

• Boiling point tester: An electronic tester can be used to measure the actual boiling temperature of the brake fluid.

• Brake fluid contamination test: To check the brake fluid, use a Styrofoam cup filled with water.

– Place a teaspoon (1 ml) of brake fluid from the master cylinder into the water.

– Pure brake fluid will completely dissolve in the water.

– Petroleum or mineral oil fluids will float on the surface of the water, retain their color, and dissolve the Styrofoam cup at the waterline.

– If the brake fluid is contaminated, the entire braking system must be drained and flushed and all rubber components replaced.

Figure 96-5 If the brake fluid is black in color, it should be replaced.

Figure 96-6 (a) A brake fluid test strip is being used to test the condition of the brake fluid.

Figure 96-6 (b) The color of the test strip is then compared with a chart on the package, which indicates the condition and if the fluid should be replaced.

Figure 96-7 An electronic tester that measures the boiling temperature of the brake fluid is useful to help determine if the brake fluid needs to be replaced.

BRAKE FLUID SERVICEBRAKE FLUID SERVICEPROCEDURESPROCEDURES

AND PRECAUTIONSAND PRECAUTIONS

Brake Fluid Service Procedures and Brake Fluid Service Procedures and PrecautionsPrecautions

1. Store brake fluid in its original container.– Purchase brake fluid in small containers– Keep all brake fluid containers tightly

closed

2. Remove any dirt, moisture, or other contamination from the top and outside of the container before opening.

3. Always discard empty brake fluid containers. Never use them for anything except brake fluid.

4. Do not transfer brake fluid to any other container that may have contained oil, kerosene, gasoline, antifreeze, water, cleaners, or any other liquids or chemicals.

5. Do not reuse brake fluid that has been siphoned from another vehicle or drawn out during a brake bleeding operation. (Brake bleeding means to open special bleeder valves in the hydraulic system to rid the system of any trapped air.)

6. Use only fresh, new brake fluid for flushing the hydraulic brake system.

• CAUTION: Alcohol or flushing fluids should not be used because they cannot be totally removed from a closed hydraulic brake system and will contaminate the system. Disassembled parts, however, can and should be cleaned with denatured alcohol or spray brake cleaner where the parts can be visually inspected to be free of cleaning solutions.

• Brake Fluid Handling and Disposal– Protective clothing and safety glasses or

goggles should be worn– Brake fluid becomes a hazardous waste if

spilled onto open ground, where it can seep into groundwater

• Brake Fluid Handling and Disposal– The disposal requirements for brake fluid

spilled onto open ground vary with the exact amount spilled and other factors

– Refer to local EPA guidelines and requirements for the exact rules and regulations in your area

RUBBER TYPESRUBBER TYPES

Rubber TypesRubber Types• Rubber products are called elastomers• Some are oil- and grease-resistant and

can be harmed by brake fluid, while others are brake-fluid resistant and can swell or expand if they come in contact with oil or grease (this swelling is necessary for the seals to withstand high hydraulic pressures)

Rubber TypesRubber Types• Silicone (DOT 5) brake fluid does not

cause rubber to swell; therefore, a rubber swell additive is used (the additive can cause SBR rubber to swell too much)

CHART 96–1 Notice that if a rubber is OK to use for brake fluid it is not OK to use for oil or grease.

Figure 96-8 The master cylinder piston seals are usually constructed from EPDM rubber, and the diaphragm of the vacuum power brake booster is usually made from SBR.

Figure 96-9 Cross-sectional view of a typical drum brake wheel cylinder. Most wheel cylinder boots and cups are either SBR or EPDM rubber.

Figure 96-10 Exploded view of a typical disc brake caliper. Both the caliper seal and dust boot are constructed of EPDM rubber.

Brake LinesBrake Lines• Terminology

– Steel brake lines are also called brake pipes or brake tubing and are used to connect the master cylinder to each wheel

– Brake lines carry brake fluid from the master cylinder to the ABS hydraulic control unit, wheel cylinders, and brake calipers

– The brake lines contain and direct the pressure of the brake hydraulic system

– Most of the brake line consists of rigid tubing

– For maximum strength and durability, all brake systems use double-walled brake tubing made from plated steel sheet

– There are two types of double-walled tubing:

• Seamless• Multiple ply

– All double-walled tubing is plated with tin, zinc, or other similar substances for protection against rust and corrosion

– All steel brake lines have one of two basic types of ends:

• Double Flare. This type is a 45 degree flare that meets SAE standard J533 also called an SAE flare)

– All steel brake lines have one of two basic types of ends:

• ISO, which means International Standards Organization (also called a ball flare or bubble flare)

Brake LinesBrake Lines• CAUTION: Copper tubing should never

be used for brake lines. Copper tends to burst at a lower pressure than steel.

Figure 96-11 Steel brake tubing is double-walled for strength and plated for corrosion resistance.

Figure 96-12 An SAE flare brake line fitting. Because of the slight difference in flare angle, double-flare fitting seals cause a wedging action.

Figure 96-13 An ISO fitting, also called a bubble or ball-type flare.

Brake LinesBrake Lines• Brake Line Replacement

– Always use a tubing cutter instead of a hacksaw to cut brake line

Figure 96-14 A tubing cutter is the preferred tool to use to cut brake line because it leaves a clean edge.

Brake LinesBrake Lines• Flaring Brake Line

– When replacing steel brake line, new steel tubing should be used and a double flare or an ISO flare completed at each end using a special flaring tool

Brake LinesBrake Lines• Flaring Brake Line

– Always use two line wrenches to disconnect or reattach brake lines

Brake LinesBrake Lines• CAUTION: According to vehicle

manufacturers’ recommended procedures, compression fittings should never be used to join two pieces of steel brake line. Only use doubleflare ends and connections, if necessary, when replacing damaged steel brake lines.

Figure 96-15 (a) Double flaring the end of a brake line. (a) Clamp the line at the correct height above the surface of the clamping tool using the shoulder of the insert as a gauge.

Figure 96-15 (b) Double flaring the end of a brake line. (b) The insert is pressed into the end of the tubing. This creates the first bend.

Figure 96-15 (c) Double flaring the end of a brake line. (c) Remove the insert and use the pointed tool to complete the overlap double flare.

Figure 96-15 (d) Double flaring the end of a brake line. (d) The completed operation as it appears while still in the clamp.

Figure 96-16 (a) Making an ISO flare requires a special tool. (a) Position the brake line into the two-part tool at the correct height using the gauge end of the tool.

Figure 96-16 (b) Making an ISO flare requires a special tool. (b) Assemble the two blocks of the tool together and clamp in a vise. Turn the tool around and thread it into the tool block. The end of the threaded part of the tool forms the “bubble” or ISO flare.

Figure 96-17 Whenever disconnecting or tightening a brake line, always use the correct size flare-nut wrench. A flare-nut wrench is also called a tube-nut wrench or a line wrench.

Brake LinesBrake Lines• Coiled Brake Line

– Steel brake line is often coiled to allow movement between the brake components without stress that could lead to metal fatigue and breakage

Figure 96-18 The coils in the brake line help prevent cracks caused by vibration.

Brake LinesBrake Lines• Armored Brake Line

– In many areas, the steel brake line is covered with a wire coil wrap

– This type of brake line is called armored brake line

Brake LinesBrake Lines• Armored Brake Line

– This armor is designed to prevent damage from stones and other debris that could dent or damage the brake line

Figure 96-19 Armored brake line is usually used in the location where the line may be exposed to rock or road debris damage. Even armored brake line can leak and a visual inspection is an important part of any brake service.

Brake LinesBrake Lines• Flexible Brake Hose

– Used on each front wheel to allow for steering and suspension movement and at the rear to allow for rear suspension travel

– These hoses can crack, blister, or leak, and should be inspected at least every six months

– Made from synthetic yarn (poly vinyl alcohol, abbreviated PVA) braided into position from multi-end yarn spindles

– Braiding the yarn allows the strength to withstand braking system pressure over 1,000 PSI (6,900 kPa)

– A typical brake hose has an inner tube and a cushion liner between the braided layers

– All three layers use ethylenepropylene- diene-monomer (EPDM)-type thermosetting polymers to prevent the hose from absorbing moisture

– An outside jacket is made from rubber and protects the reinforcement fabric from moisture and abrasion

– The outside covering is also ribbed to hide surface blemishes

– It is not unusual for flexible brake lines to become turned around and twisted during a brake pad change

– A constricted brake hose can cause the brakes to remain applied, causing excessive brake pad wear and unequal braking

– A constricted flexible brake line can also cause the vehicle to pull to one side

– Always replace flexible brake hoses in pairs

Brake LinesBrake Lines• CAUTION: Never allow a disc brake

caliper to hang by the flexible brake hose. Damage to the line can result. Always use a wire to support the weight of the caliper.

Figure 96-21 Flexible brake hoses are used between the frame or body of the vehicle and the wheel brakes. Because of suspension and/or steering movement, these flexible brake lines must be strong enough to handle high brake fluid pressures, yet remain flexible. Note that this flexible brake hose is further protected against road debris with a plastic conduit covering.

Figure 96-22 (a) Typical flexible brake hose showing the multiple layers of rubber and fabric.

Figure 96-22 (b) The inside diameter (ID) is printed on the hose (3 mm).

Figure 96-23 Brake hose fabric being woven at the factory.

Figure 96-24 Typical flexible brake hose faults. Many faults cannot be seen, yet can cause the brakes to remain applied after the brake pedal is released.

Figure 96-25 Flexible brake hose should be carefully inspected for cuts or other damage, especially near sections where the brake hose is attached to the vehicle. Notice the crack and cut hose next to the mounting bracket.

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