1996 Bronco/F-Series

Section 06-00: Brake System, Service

1996 F-150, F-250, F-350, F-Super Duty Chassis Cab, Motorhome Chassis and Bronco Workshop Manual

DIAGNOSIS AND TESTING

Pinpoint Tests

PINPOINT TEST A: BRAKES PULL OR DRIFT

A1 INSPECT TIRE PRESSURE

Measure air pressure in all four tires.

Is tire pressure within specifications?

Yes	No
GO to A2.	ADJUST tire pressure.

A2 CHECK CALIPER PISTONS AND PINS

Check the front disc brake caliper pistons, pins or rear wheel cylinders for binding or sticking.

Do the front disc brake caliper pistons, pins or rear wheel cylinders bind or stick?

Yes	No
REPAIR or REPLACE components as necessary.	GO to A3.

A3 INSPECT FRONT DISC BRAKE ROTORS AND DRUMS

Inspect the front disc brake rotor and brake drum for excessive runout or damage.

Does excessive runout or damage exist?

Yes	No
REPAIR or REPLACE front disc brake rotor or brake drum as necessary.	GO to A4.

A4 INSPECT WHEEL BEARINGS

Inspect front and rear wheel bearings for excessive end play or improper preload.

Does excessive end play or improper wheel bearing preload exist?

Yes	No
ADJUST rear wheel bearing preload or REPLACE wheel bearings.	PERFORM a hydraulic leak check. REFER to Pinpoint Test M for vehicles equipped with vacuum boost system. REFER to Pinpoint Test Q for vehicles equipped with Hydro-Boost system.

PINPOINT TEST B: RED BRAKE WARNING INDICATOR ALWAYS ON

B1 CHECK PROPER FUNCTION OF BRAKE WARNING INDICATOR WHEN RELEASED

Key on or in ACCY.
Verify parking brake is fully released.

Is the red brake warning indicator on?

Yes	No
GO to B3.	GO to B2.

B2 CHECK PROPER FUNCTION OF BRAKE WARNING INDICATOR WHEN SET

Set parking brake.

Does the red brake warning indicator come on?

Yes	No
Brake warning indicator bulb and circuits are functioning properly.	GO to B9.

B3 CHECK BRAKE FLUID LEVEL IN BRAKE MASTER CYLINDER

Check the brake fluid level at the brake master cylinder reservoir.

Is the brake fluid level within specification?

Yes	No
GO to B4.	CHECK for leaks in the vehicle brake system and REPAIR as required. FILL the brake master cylinder reservoir to the required level. REPEAT B1.

B4 VERIFY FLOAT BUOYANCY

Remove the brake master cylinder filler cap from the brake master cylinder reservoir.
Using a clean steel implement, attempt to push the float down.

Does the float move down?

Yes	No
GO to B5.	REPLACE the brake master cylinder reservoir. BLEED the brake system. REPEAT B1.

B5 CHECK REAR ANTI-LOCK BRAKE SYSTEM (RABS) MODULE

Key off.
Disconnect RABS module harness connector.
Key on.

Does the brake warning indicator turn on?

Yes	No
RECONNECT RABS module connector. GO to B6.	REPLACE anti-lock brake control module. RECONNECT RABS module connector. REPEAT B1.

B6 LOCATE CAUSE OF RED BRAKE WARNING INDICATOR ON

Key off.
Disconnect the fluid level switch harness connector from the brake master cylinder reservoir.
Key on.

Does the brake warning indicator turn on?

Yes	No
Diesel only: GO to B7. All others: GO to B8.	GO to B9.

B7 LOW VACUUM SWITCH CHECK (DIESEL ONLY)

Key off.
Disconnect low vacuum switch harness connector.
Key on.

Does the brake warning indicator turn on?

Yes	No
GO to B8.	RECONNECT all loose connections. REFER to Section 06-07B to diagnose reason for low vacuum switch actuating the brake warning indicator.

B8 PARKING BRAKE SWITCH

Key off.
Disconnect parking brake switch harness connector.
Key on.

Does the brake warning indicator turn on?

Yes	No
LOCATE and SERVICE short to ground in Circuit 977 (P/W), 640 (R/Y), 531 (DG/Y), or 162. RECONNECT all loose connections. REPEAT B1.	REPLACE parking brake switch. RECONNECT all loose connections. REPEAT B1.

B9 BRAKE WARNING INDICATOR TEST

NOTE: The brake warning indicator should only light when the ignition switch is in the START position or when the ignition switch is on and the parking brake is applied (gasoline), or when the vacuum is low (diesel).

Release parking brake.
Check brake fluid level in brake master cylinder reservoir. Fill as required.
Key in ACCY or on.

Does brake warning indicator turn on?

Yes	No
CHECK switch wiring for possible short to ground. REPAIR or REPLACE as required. GO to B10.	GO to B11.

B10 MASTER CYLINDER FLUID LEVEL SWITCH WIRING CHECK

Partially drain the brake master cylinder reservoir.
Key to RUN and observe brake warning indicator.

Does the brake warning indicator illuminate?

Yes	No
FILL brake master cylinder reservoir. Switch OK.	CHECK for open in fluid level switch to brake warning indicator wiring. SERVICE as required. If no open found, GO to B11.

B11 MASTER CYLINDER LEVEL SWITCH CHECK

Manually push the float in the brake master cylinder reservoir to the bottom.
Key to RUN and observe the brake warning indicator.

Does the brake warning indicator illuminate?

Yes	No
REFILL brake master cylinder reservoir. Switch OK.	GO to B12.

B12 CHECK FLUID LEVEL SWITCH

Key off.
With the fluid level switch harness connector disconnected, jumper between Circuits 512 (T/LG) and 531 (DG/Y).
Key on.

Does the brake warning indicator turn on?

Yes	No
LOCATE and SERVICE short to ground in Circuit 512 (T/LG). RECONNECT all loose connections. REPEAT B1.	REPLACE brake master cylinder reservoir. BLEED brake system. RECONNECT all loose connections. REPEAT B1.

PINPOINT TEST C: VIBRATION WHEN BRAKES ARE APPLIED

C1 ISOLATE VIBRATION/SHUDDER

Determine if vibration/shudder is induced by the rear brakes by using the parking brake to slow the vehicle from approximately 80 km/h to 56 km/h (50 mph to 35 mph).
To use the parking brake, hold the release handle out while depressing the parking brake pedal with the left foot.

Is vibration/shudder present?

Yes	No
CHECK the rear brakes. GO to C2 for disc brakes. GO to C3 for drum brakes.	CHECK the front brakes. GO to C2.

C2 DISC BRAKES

Resurface front disc brake rotors and road test vehicle.

Is shudder/vibration present?

Yes	No
GO to C4.	Brake system repaired.

C3 BRAKE DRUMS

Refinish brake drums and road test vehicle.

Is shudder/vibration present?

Yes	No
GO to C5.	Brake system repaired.

C4 DISC BRAKE PADS

Replace disc brake pads and road test vehicle.

Is shudder/vibration present?

Yes	No
REPLACE front disc brake rotors.	Brake system repaired.

C5 BRAKE SHOES AND LININGS

Replace rear brake shoes and linings and road test vehicle.

Is shudder/vibration present?

Yes	No
REPLACE drums.	Brake system repaired.

PINPOINT TEST D: PEDAL GOES DOWN FAST

D1 ROAD TEST

Road test vehicle only if condition cannot be verified in shop.
Statically depress brake pedal.

Does brake pedal operate properly?

Yes	No
Vehicle OK.	GO to D2.

D2 BRAKE FLUID LEVEL

Check brake fluid level.

Is fluid level within specifications?

Yes	No
GO to D3.	CHECK reservoir sealing points. ADD fluid and BLEED system. REPEAT D1.

D3 PRESSURIZE SYSTEM

Pump brake pedal rapidly (five times).

Does brake pedal height build and maintain throughout test?

Yes	No
CHECK rear brake adjustment and ADJUST if necessary. If condition still exists, BLEED system. REPEAT D1.	GO to D4.

D4 BRAKE SYSTEM LEAKS

Perform Pinpoint Test Q in this section and return to this test step.

Does system leak?

Yes	No
SERVICE as necessary. ADD fluid and BLEED system. REPEAT D1.	System OK.

PINPOINT TEST E: PEDAL GOES DOWN SLOWLY

E1 ROAD TEST

Check if condition occurs during actual stopping application by depressing the brake pedal while the vehicle is moving.

Does the condition occur only when vehicle is stationary?

Yes	No
Normal condition. No action required.	Condition occurs while vehicle is moving and braking; performance is affected. GO to E2.

E2 RECHECK BRAKE SYSTEM LEAKS

Perform Pinpoint Test Q in this section and return to this test step.

Does system leak?

Yes	No
SERVICE as necessary, ADD fluid and BLEED system. REPEAT E1.	GO to E3.

E3 MASTER CYLINDER TEST

Perform Pinpoint Test M in this section and return to this test step.

Is test OK?

Yes	No
System OK.	REPLACE damaged parts, ADD fluid and BLEED system. REPEAT E1.

PINPOINT TEST F: PEDAL IS LOW OR FEELS SPONGY

F1 BRAKE PEDAL CHECK

Statically apply brake pedal.
Road test vehicle only if condition cannot be verified in shop.

Does brake pedal operate properly?

Yes	No
Vehicle OK.	GO to F2.

F2 BRAKE PEDAL RESERVE CHECK

Key on, engine running at idle with transmission in PARK or NEUTRAL.
Depress brake pedal lightly three or four times.
Wait 15 seconds to allow the vacuum to replenish.
Push down on brake pedal until it stops moving downward or an increased resistance to the brake pedal travel occurs.

NOTE: This increased resistance may feel like the pedal has bottomed out.

Hold the brake pedal in the applied position while increasing the engine speed to 2000 rpm.
Release the accelerator pedal.

Does the brake pedal move downward as engine speed returns to normal?

Yes	No
GO to F3.	CHECK vacuum to power brake booster. REFER to Section 06-07A or Section 06-07B.

F3 BRAKE FLUID LEVEL CHECK

Check brake fluid level.

Is brake fluid level within specifications?

Yes	No
GO to F4.	CHECK brake master cylinder reservoir sealing points. ADD fluid and BLEED system.

F4 FILLER CAP VENT CHECK

Check if brake master cylinder filler cap vent holes are clogged or dirty.

Are holes clogged or dirty?

Yes	No
CLEAN as necessary. REPEAT F1.	GO to F5.

F5 BLEED BRAKE SYSTEM

Bleed brake system as described in this section.

Has the condition been corrected?

Yes	No
Vehicle OK.	GO to F6.

F6 FRONT WHEEL BEARING ADJUSTMENT

Check front wheel bearings for proper adjustment.

Are bearings properly adjusted?

Yes	No
CHECK rear brake adjustment and ADJUST if necessary. REPEAT F1.	ADJUST front wheel bearings. REPEAT F1.

PINPOINT TEST G: BRAKE LOCKUP DURING LIGHT BRAKE PEDAL FORCE

G1 TIRE CHECK

Check tires for uneven wear and correct pressure.

Is there a wear or pressure concern?

Yes	No
CORRECT tire concern. REFER to Section 04-04.	GO to G2.

G2 BRAKE SHOE AND LINING CHECK

Inspect brake shoe and linings for contamination, correct installation, damage, correct size and type.

Is there a brake shoe and lining concern?

Yes	No
REPAIR or REPLACE brake shoe and lining. REFER to Section 06-02, Section 06-03 or Section 06-04.	GO to G3.

G3 PARKING BRAKE CHECK

Inspect parking brake components for damage or seized condition.

Is there a parking brake concern?

Yes	No
CORRECT parking brake concern. REFER to Section 06-05.	GO to G4.

G4 WHEEL BEARING CHECK

Raise vehicle enough to relieve weight on tires.
Pull alternately on front and rear of each tire to check for loose or damaged wheel bearings.

Is there a wheel bearing concern?

Yes	No
CORRECT the wheel bearing concern. REFER to the appropriate section in Group 04 or Group 05.	GO to G5.

G5 POWER BRAKE BOOSTER PUSH ROD CHECK

Support the brake master cylinder and remove the brake master cylinder mounting nuts.
Position the brake master cylinder out of the way.
With a shop-fabricated gauge, check the power brake booster push rod adjustment.
The exposed end of the power brake booster push rod should be within 24.89-25.27mm (0.980-0.995 in.) of the brake master cylinder mounting surface on the power brake booster.

Does the power brake booster push rod require adjustment?

Yes	No
ADJUST as necessary. REFER to Section 06-07A.	GO to G6.

G6 ABS HYDRAULIC CONTROL UNIT (HCU) CHECK (BRONCO ONLY); REAR ANTI-LOCK BRAKE SYSTEM (RABS) (F-SERIES EXCEPT SUPER DUTY)

Perform the appropriate diagnostic tests in Section 06-09A or Section 06-09B to check for defective dump valve and return to this test step.

Is there an HCU or RABS concern?

Yes	No
REPAIR or REPLACE the HCU. REFER to Section 06-09A or Section 06-09B.	CHECK for possible brake fluid contamination.

PINPOINT TEST H: EXCESSIVE AND/OR ERRATIC PEDAL TRAVEL

H1 ROUGH ROAD TEST

Road test vehicle under rough road conditions.
Apply brakes slowly.

Are brakes good?

Yes	No
Vehicle OK.	GO to H2.

H2 WHEEL BEARING CHECK

Check for loose front wheel bearings.

Are front wheel bearings loose?

Yes	No
REPLACE front wheel bearing if damaged. TIGHTEN front wheel bearing assembly to specification. REPEAT H1.	CHECK front disc brake rotor for thickness variances. REFER to Section 06-03.

PINPOINT TEST J: FRONT BRAKES DRAG

J1 BRAKE FUNCTION TEST

Road test vehicle and apply brakes.

Are brakes functional?

Yes	No
Vehicle OK.	CHECK power brake vacuum booster push rod. REPEAT J1.

PINPOINT TEST K: BRAKE PEDAL EFFORT EXCESSIVE, BOOSTER SYSTEM OK

K1 BRAKE PEDAL LINKAGE TEST

Detach booster push rod from brake pedal pin and depress brake pedal fully.

Has condition been corrected?

Yes	No
CHECK power brake booster vacuum availability. REFER to Section 06-07A or Section 06-07B.	SERVICE or REPLACE brake pedal linkage. VERIFY system OK.

PINPOINT TEST L: SLOW OR INCOMPLETE BRAKE PEDAL RETURN

L1 BRAKE PEDAL RETURN

Run engine at fast idle while making several brake applications.
Pull brake pedal rearward with approximately 44.5N (10 lbs.) force.
Release the brake pedal and measure the distance to the toe board.
Make a hard brake application.
Release the brake pedal and measure the brake pedal to toe board distance. The brake pedal should return to its original position.

Did brake pedal return to original position?

Yes	No
Vehicle OK.	GO to L2.

L2 BRAKE PEDAL BINDING

Check brake pedal for sticking or binding.

Is the brake pedal operating freely?

Yes	No
REPLACE power brake booster.	CORRECT any sticking or binding. REPEAT L2.

PINPOINT TEST M: LOSS OF BRAKE FLUID

M1 CHECK FOR LEAKS

Apply the brakes and check for leaks.

Are any leaks found?

Yes	No
REPLACE leaking parts as required.	GO to M2.

M2 REAR BRAKE LEAK CHECK

Remove brake drum.
Inspect all rear wheel cylinders for leaks.

Do rear wheel cylinders check OK?

Yes	No
GO to M3.	REPLACE or REBUILD rear wheel cylinders as required.

M3 FRONT BRAKE LEAK CHECK

Inspect front disc brake calipers for leaks.

Do front disc brake calipers check OK?

Yes	No
GO to M4.	REPLACE or REBUILD front disc brake calipers as required.

M4 MASTER CYLINDER CHECK

Disconnect the brake master cylinder connector tubes from the master cylinder.
Plug the output ports using the appropriate size flared tube type plugs.
Push down hard on the brake pedal.

Does the brake pedal slowly move downward?

Yes	No
REPLACE or REBUILD the brake master cylinder as required.	Hydraulic system checks OK.

PINPOINT TEST N: EXCESSIVE PEDAL EFFORT, VACUUM BOOST SYSTEM

N1 VACUUM CHECK

Disconnect vacuum booster hose from booster.
Connect Rotunda Vacuum/Pressure Tester 164-R0253 or Rotunda Vacuum Tester 014-R1054 or equivalent to the vacuum hose with a T-fitting.
Key on, engine running. Allow engine to reach normal operating temperature.
Record the vacuum pressure.

Is the vacuum reading 57-70 kPa (17-21 in-Hg)?

Yes	No
GO to N2.	TUNE UP or REPAIR engine as required.

N2 SYSTEM INSPECTION

Key off.
Reconnect the vacuum line.
Inspect power brake booster check valve, rubber grommet and all vacuum plumbing for cracks, holes, bad connections or missing clamps.
Push down on brake pedal and hold.
Key on, engine running.

Does the brake pedal move downward when the engine is started?

Yes	No
Vacuum system is OK.	GO to N3 for diesel engines. GO to N4 for gas engines.

N3 VACUUM DROP CHECK, DIESEL ONLY

Key off.
Disconnect the vacuum line and connect a vacuum gauge with a T-fitting to the lower part of dash-mounted plastic check valve.
Key on, engine running at idle until vacuum reaches 57-70 kPa (17-21 in-Hg).
Key off.
Observe vacuum gauge for 1 minute.

Does vacuum pressure drop more than 1 in-Hg?

Yes	No
REPLACE power brake booster check valve.	GO to N4.

N4 COMPONENT ISOLATION CHECK

Key off.
Reconnect the vacuum gauge to the same point as in Step N1, but leave the rest of the system connected.
Key on, engine running at idle until vacuum reaches 57-70 kPa (17-21 in-Hg).
Key off.
Observe vacuum gauge for 1 minute.

Does vacuum pressure drop more than 1 in-Hg?

Yes	No
DISCONNECT each component one at a time and REPEAT the test procedures in N4 until the leaking component is found. PLUG the disconnected vacuum line while performing the test procedures. REPAIR or REPLACE as required. On diesel engines with dash-mounted power brake booster, REPLACE power brake booster check valve also.	GO to N5.

N5 BOOSTER LEAK CHECK

Key on.
Run engine until vacuum pressure reaches 57-70 kPa (17-21 in-Hg).
Key off.
Push down on the brake pedal and hold for a few seconds and release.

Does the vacuum drop to 0 kPa (0 in-Hg)?

Yes	No
REPLACE power brake booster.	System checks OK. REMOVE vacuum gauge and RECONNECT all vacuum lines.

PINPOINT TEST P: EXCESSIVE PEDAL EFFORT, HYDRO-BOOST SYSTEM

P1 FLUID LEVEL

Check power steering pump fluid level.

Is fluid level within specifications?

Yes	No
GO to P2.	CHECK Hydro-Boost leak points. ADD fluid as required.

P2 BELT CHECK

Check the power steering belt tension, and condition.

Is drive belt OK?

Yes	No
GO to P3.	ADJUST belt tension as required. REFER to Section 03-05.

P3 CHECK POWER STEERING HOSES

Check power steering right turn pressure hose, power steering left turn pressure hose and power steering return hose for cracks or leaks.

Do power steering right turn pressure hose, power steering left turn pressure hose and power steering return hose check OK?

Yes	No
GO to P4.	SERVICE or REPLACE as required. REFER to Section 11-00.

P4 CHECK BRAKE PEDAL LINKAGE

Check the brake pedal linkage for binding or sticking operation.

Does linkage check OK?

Yes	No
GO to P5.	SERVICE or REPLACE as required. REFER to Section 06-06.

P5 PUMP SPEED

Check engine idle speed against specifications.

Is engine idle speed OK?

Yes	No
GO to P6.	SET engine idle speed to specifications.

P6 PUMP FLOW AND RELIEF

Test the power steering pump for proper flow and relief pressure.

Is power steering pump operating properly?

Yes	No
REPLACE power brake booster.	REPAIR or REPLACE power steering pump as required. REFER to Section 11-00.

PINPOINT TEST Q: BRAKE FLUID LOSS, HYDRO-BOOST SYSTEM

Q1 BASIC CHECK

Key off.
Depress and release brake pedal several times to deplete all hydraulic pressure from the Hydro-Boost power brake booster.
Depress and hold the brake pedal with light pressure.
Key on, engine running.

Does the brake pedal fall slightly and then hold, and is less pressure now required to hold the brake pedal at this position?

Yes	No
Hydro-Boost power brake booster is OK.	GO to Q2.

Q2 BRAKE HYDRAULIC LEAK CHECK

Depress and release the brake pedal several times.
Hold the brake pedal down with medium pressure of 111-156 N (25-35 lbs.).

Does the brake pedal fall away?

Yes	No
GO to Q3.	GO to Q4.

Q3 EXTERNAL LEAK CHECK

Check for leaks at power steering return line hoses, brake lines, brake master cylinder and hoses.

Do components check OK?

Yes	No
SERVICE or REPAIR the brake master cylinder internal leak as required. REFER to Section 06-00.	REPAIR or REPLACE as required. REFER to Section 06-06.

Q4 HYDRO-BOOST HOSE CONNECTIONS LEAK CHECK

Clean the Hydro-Boost power brake booster, power steering right turn pressure hose, power steering left turn pressure hose and power steering return hose and connections.
Key on, engine running at idle speed.
Check the Hydro-Boost hose connections for leaking.

Do the hose connections check OK?

Yes	No
GO to Q5.	SERVICE or REPLACE power steering right turn pressure hose, power steering left turn pressure hose and power steering return hose and connections as required.

Q5 HYDRO-BOOST LEAK CHECK

Key on, engine running at idle speed.
Apply the brake pedal with approximately 444 N (100 lbs.) force of pressure and hold.

CAUTION: Do not hold the brake pedal at 444 N (100 lbs.) force for more than 5 seconds at a time.

Check the Hydro-Boost power steering right turn pressure hose, power steering left turn pressure hose and power steering return hose for leaks.

Do the hoses check OK?

Yes	No
GO to Q6.	REPLACE the Hydro-Boost power brake booster.

Q6 RESERVE RETENTION CHECK

Key on, engine running at idle speed.
Charge system pressure by holding the steering wheel on the stop, or by pressing down on the brake pedal with approximately 444 N (100 lbs. force).
Key off.
Wait 8 to 12 minutes.
Depress the brake pedal.

Is there any power reserve?

Yes	No
Hydro-Boost power brake booster is OK.	REPLACE the Hydro-Boost power brake booster.