Section 06-00: Brake System—Service
1994 Mustang Workshop Manual
DIAGNOSIS AND TESTING

Pinpoint Tests

  

PINPOINT TEST A: BRAKES PULL OR DRIFT

 

A1 ROAD TEST VEHICLE

Yes
GO to A2.

No
Vehicle OK.

 

A2 TIRE INSPECTION

Yes
GO to A3.

No
INFLATE tires to proper pressure. REPLACE excessively worn tires. REPEAT TestA1.

 

A3 BRAKE PAD INSPECTION

  • Inspect brake shoe and lining for grease or fluid on linings and/or wear concerns.
Yes
GO to A4.

No
REPEAT Test A1.

 

A4 PRESSURE CONTROL VALVE TEST—FRONT

  • Install pressure gauges in the LH front and RH rear bleeder screws. Apply 6895 kPa (1000 psi) in front brake system. The RH rear brake pressure must be between 6205-7584 kPa (900-1100 psi).
  • Is rear brake pressure between 6205-7584 kPa (900-1100 psi)?
Yes
INSPECT calipers and REPLACE as required.

No
REPLACE RH rear brake pressure control valve.

 

A5 PRESSURE CONTROL VALVE TEST—REAR

  • Install pressure gauges in RH front and LH rear bleeder screws. Apply 4136-4688 kPa (600-680 psi) in front brake system. The LH rear brake pressure must be between 3964-4343 kPa (575-630 psi).
  • Is rear brake pressure between 3964-4343 kPa (575-630 psi)?
Yes
INSPECT calipers and REPLACE as required.

No
REPLACE LH rear brake pressure control valve.

  

PINPOINT TEST B: BRAKE WARNING LAMP INOPERATIVE

 

B1 BRAKE FLUID LEVEL

  • Check brake master cylinder reservoir fluid level.
  • Is fluid level good?
Yes
GO to B3.

No
GO to B2.

 

B2 BRAKE SYSTEM LEAKAGE

  • Check brake master cylinder reservoir sealing points and external brake system for leakage. (Refer to Diagnostic TechniquesNo. 1 and No. 3.)
  • Does system leak?
Yes
SERVICE as necessary, ADD fluid and BLEED system.

No
FILL brake master cylinder reservoir . GO to B3.

 

B3 IGNITION WIRING CHECK

  • Check that ignition wiring is not within a 50.8mm (2 inch) radius of the reed switch Fluid Level Indicator (FLI) assembly.
  • Is ignition wiring OK?
Yes
GO to B4.

No
REROUTE wiring as necessary.

 

B4 FLOAT ASSEMBLY CHECK

  • Check if float is stuck or magnet is dislodged from float.
  • Is float functional?
Yes
CHECK if ignition prove out circuit is working properly.

No
REPLACE brake master cylinder reservoir assembly.

  

PINPOINT TEST C: VIBRATION WHEN BRAKES ARE APPLIED

 

C1 ROAD TEST

  • Road test vehicle without applying brakes 40-80 km/h (25-50 mph).
  • Is a vibration present?
Yes
REFER to Section 00-04 to service this condition first. REPEAT Step.

No
GO to C2.

 

C2 REAR BRAKE VIBRATION

  • Road test vehicle with medium application on the parking brake control only.

    NOTE: With manual release parking brake control , hold the parking brake control in release position during parking brake control application.

  • Was a vibration present?
Yes
CHECK rear disc brake rotor for excessive wear or runout. REFER to Section 06-04 for rear disc brake procedures.

No
GO to C3.

 

C3 FRONT BRAKE VIBRATION

  • Road test vehicle with light and medium application on the brake pedal .
  • Was a vibration present?
Yes
CHECK front disc brake rotors for excessive runout or cracks. REFER to Section 06-03 for disc brake rotor procedures. REPEAT Step C3.

No
Vehicle OK.

  

PINPOINT TEST D: PEDAL GOES DOWN FAST

 

D1 PEDAL FEEL

  • Road test vehicle and apply brake pedal .
  • Was brake pedal effort normal?
Yes
Vehicle OK.

No
GO to D2.

 

D2 BRAKE FLUID LEVEL

  • Check brake master cylinder reservoir fluid level.
  • Is fluid level acceptable?
Yes
GO to D3.

No
CHECK brake master cylinder reservoir sealing points (use Diagnostic Technique No. 3), ADD fluid and BLEED system. REPEAT Test D1.

 

D3 PRESSURIZE SYSTEM

  • Pump brake pedal rapidly (five times).
  • Does the brake pedal height build up and then hold?
Yes
CHECK rear brake adjustment and ADJUST if necessary. If condition still exists, BLEED system for air. REPEAT Test D1.

No
GO to D4.

 

D4 BRAKE SYSTEM LEAKS

  • Check for external brake system leaks (use Diagnostic Technique No. 1).
  • Any leaks found?
Yes
SERVICE as necessary, ADD fluid and BLEED system. REPEAT Test D1.

No
GO to D5.

 

D5 MASTER CYLINDER BYPASS TEST

  • Test for brake master cylinder bypass (use Diagnostic Technique No. 2).
  • Was a concern found?
Yes
REPLACE damaged parts, ADD fluid and BLEED system. REPEAT Test D1.

No
System OK.

  

PINPOINT TEST E: PEDAL EASES DOWN SLOWLY

 

E1 CHECK BRAKE PEDAL OPERATION

  • Check if condition occurs during actual stopping application by applying the brake pedal while the vehicle is moving.
  • Does condition occur with vehicle stationary?
Yes
No action required. (REFER to Normal Condition No.1.)

No
GO to E2.

 

E2 BRAKE SYSTEM LEAKS

  • Were any leaks found?
Yes
SERVICE as necessary. ADD fluid and BLEED system. REPEAT Test E1.

No
GO to E3.

 

E3 BRAKE MASTER CYLINDER BYPASS TEST

  • Was a problem found?
Yes
REPLACE damaged parts, ADD fluid and BLEED system. REPEAT Test E1.

No
System OK.

  

PINPOINT TEST F: PEDAL IS LOW OR FEELS SPONGY

 

F1 SPONGY PEDAL

  • Road test vehicle and apply brake pedal .
  • Was brake pedal effort normal?
Yes
Vehicle OK.

No
GO to F2.

 

F2 BRAKE FLUID LEVEL CHECK

  • Check brake master cylinder reservoir fluid level.
  • Is fluid level acceptable?
Yes
GO to F3.

No
CHECK brake master cylinder reservoir sealing points. (USE Diagnostic Technique No. 3) ADD fluid and BLEED system.

 

F3 FILLER CAP VENT CHECK

  • Check if filler cap vent holes are clogged or dirty.
  • Was a concern found?
Yes
CLEAN as necessary. REPEAT Test F1.

No
GO to F4.

 

F4 BLEED BRAKE SYSTEM

  • Bleed brake system as described in this Section.
  • Is condition still present?
Yes
GO to F5.

No
Vehicle OK.

 

F5 FRONT HUB NUT CHECK

  • Check front axle wheel hub retainer nut for looseness, (refer to Section 04-01).
  • Was hub nut loose?
Yes
REPLACE with new nut and stake. Do not reuse the front axle wheel hub retainer . REPEAT Test F1.

No
CHECK rear brake adjustment and ADJUST if necessary. REPEAT Test F1.

  

PINPOINT TEST G: PEDAL EFFORT EXCESSIVE

 

G1 CHECK BRAKE PEDAL BUILDUP

  • Depress brake pedal fully several times.
  • Does brake pedal build up?
Yes
Vehicle is OK.

No
GO to G2.

 

G2 FLUID CONTROL VALVE CHECK

  • Check brake pressure control valve for contamination. (Refer to Fluid Control Valve Assembly removal and installation procedure in Section 06-06.)
  • Is fluid contaminated?
No
GO to G3.

Yes
REPLACE brake pressure control valve . FILL brake master cylinder reservoir . REPEAT Test G1.

 

G3 BRAKE PEDAL LINKAGE TEST

  • Detach booster push rod from pedal pin and depress brake pedal fully.
  • Did pedal move freely?
Yes
CHECK booster vacuum availability as described under Vacuum Booster Diagnosis in this Section.

No
SERVICE or REPLACE brake pedal linkage. REPEAT Test G1.

  

PINPOINT TEST H: REAR BRAKE LOCKUP DURING LIGHT BRAKE PEDAL FORCE

 

H1 BRAKE LOCK UP TEST

  • Road test vehicle and apply brake pedal lightly.
  • Do brakes lock up?
Yes
GO to H4 and H5.

No
Vehicle OK.

 

H2 TIRE INSPECTION

  • Check for excessive tire wear or improper tire pressures.
  • Are tires good?
Yes
GO to H3.

No
SUBSTITUTE known good tires if worn. INFLATE to proper pressure. REPEAT Test H1.

 

H3 BRAKE PAD INSPECTION

  • Inspect brake shoes and linings for grease or fluid on linings and/or wear concerns.
  • Are there concerns?
Yes
GO to H4.

No
REPLACE if necessary. REPEAT Test H1.

 

H4 PRESSURE CONTROL VALVE TEST—FRONT

  • Install pressure gauges in the LH front and RH rear bleeder screws. Apply 6895 kPa (1000 psi) in front brake system. The RH rear brake pressure must be between 6205-7584 kPa (900-1100 psi).
  • Is rear brake pressure between 6205-7584 kPa (900-1100 psi)?
Yes
INSPECT calipers and REPLACE as required.

No
REPLACE RH rear brake pressure control valve .

 

H5 PRESSURE CONTROL VALVE TEST—REAR

  • Install pressure gauges in RH front and LH rear bleeder screws. Apply 4136-4688 kPa (600-680 psi) in front brake system. The LH rear brake pressure must be between 3964-4343 kPa (575-630 psi).
  • Is rear brake pressure between 3964-4343 kPa (575-630 psi)?
Yes
INSPECT calipers and REPLACE as required.

No
REPLACE LH rear brake pressure control valve .

  

PINPOINT TEST I: EXCESSIVE AND/OR ERRATIC PEDAL TRAVEL

 

I1 ROUGH ROAD TEST

  • Road test vehicle under rough road conditions. Apply brakes slowly.
  • Are brakes good?
Yes
Vehicle OK.

No
GO toI2.

 

I2 WHEEL BEARING CHECK

  • Check for loose front wheel bearings .
  • Are front wheel bearings loose?
Yes
REPLACE front wheel bearing if damaged. TIGHTEN front wheel bearing assembly to specification. REPEAT Test I1.

No
CHECK front disc brake rotor for thickness variances. (REFER to
Section 06-03.)

  

PINPOINT TEST J: FRONT BRAKES DRAG

 

J1 CHECK FLUID CONTROL VALVE

  • Road test vehicle and apply brakes.
  • Are brakes functional?
Yes
Vehicle OK.

No
INSPECT fluid control valve for contamination. (REFER to Fluid Control Valve Assembly procedure in this section.) GO to J2.

 

J2 CHECK POWER BRAKE BOOSTER

  • Road test vehicle and apply brakes.
  • Are brakes functional?
Yes
Vehicle OK.

No
CHECK power brake booster push rod adjustment.

  

PINPOINT TEST K: EXCESSIVE BRAKE PEDAL EFFORT

 

K1 CHECK BRAKE APPLICATION

  • With engine off, apply and release brake pedal five times to deplete all vacuum from power brake booster . Depress brake pedal, hold with light pressure. Start engine.
  • Does the brake pedal hold?
Yes
GO toK2.

No
GO to K4.

 

K2 VACUUM BOOSTER LEAK TEST

  • Run engine to medium idle, release accelerator pedal and shaft and turn engine off. Wait 90 seconds and apply brakes. Two or more applications should be power assisted.
  • Does power brake booster work?
Yes
Vehicle OK.

No
GO to K3.

 

K3 POWER SECTION CHECK VALVE TEST

  • Disconnect vacuum hose for power brake booster check valve at manifold. Blow into hose attached to power brake booster check valve .
  • Does air pass through valve?
Yes
INSTALL new power brake booster check valve and REPEAT Step K2.

No
REPLACE power brake booster . REPEAT Step K1.

 

K4 POWER SECTION TEST

  • Disconnect vacuum hose from power brake booster check valve . Run engine at idle. Check vacuum supply with a vacuum gauge.
  • Is pressure above 40.5 kPa (12 in-Hg) with brake booster non-operational?
Yes
REPLACE power brake booster . REPEAT Step K1.

No
SERVICE or REPLACE vacuum hose and vacuum fittings. Also TUNE or SERVICE engine as required. REPEAT Step K1.

  

PINPOINT TEST L: BRAKE NOISE

 

L1 PEDAL NOISE

  • Run engine at fast idle for 10 seconds or longer. Apply brake pedal and listen for noise. Compare results with known good system.
  • Was a noise present?
Yes
GO to L2.

No
Vehicle OK.

 

L2 PUSH ROD ADJUSTMENT

  • Check and adjust power brake booster push rod.
  • Is push rod adjustment OK?
Yes
BLEED brake system.

No
REPLACE power brake booster . REPEAT Step L1.

  

PINPOINT TEST M: SLOW OR INCOMPLETE BRAKE PEDAL RETURN

 

M1 BRAKE PEDAL RETURN

  • Run engine at fast idle while making several brake applications. Pull brake pedal rearward with approximately 44.5 N (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
Vehicle OK.

No
GO to M2.

 

M2 BRAKE PEDAL BINDING

  • Check brake pedal to be sure it is operating freely.
  • Is the brake pedal operating freely?
Yes
REPLACE power brake booster.

No
CORRECT any sticking or binding. REPEAT M2.