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Brake Master Cylinder

Brakes and Traction Control › Hydraulic System
Unified entry — merged from multiple cross-listed pages in the original manual.

Parts

PartFrom 01/07/08
ManufacturerCHY
OEM part #68091278AB
Price$146.00
NotesIncludes: Reservoir.

Labor

Replace — Master Cylinder1.0 hr
Warranty 0.0 hrSkill B
Master Cylinder Reservoir0.7 hr
Warranty 0.0 hrSkill B
Procedures
Procedures4 steps
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Fig. 2
  1. Mount master cylinder in vise.
  2. Attach bleed tubes to cylinder outlet ports. Then position each tube end into reservoir (Figure 1).
  3. Fill reservoir with fresh brake fluid.
  4. Press cylinder pistons inward with wood dowel. Then release pistons and allow them to return under spring pressure. Continue bleeding operations until air bubbles are no longer visible in fluid.
Brake Master Cylinder Reservoir - Removal7 steps
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Fig. 4
  1. Install prop rod on brake pedal to keep pressure on the brake system.
  2. Remove reservoir cap and siphon fluid into drain container.
  3. Remove the electrical connector (3) from the fluid level switch in the reservoir (2).
  4. Remove the reservoir (1) from the master cylinder by pulling the four tabs (3) outward to release.
  5. Remove the reservoir (1) from the master cylinder by pulling upwards.
  6. If replacing the reservoir (1) remove the fluid level sensor (2) by squeezing the tabs together while pulling on the sensor (2).
  7. Remove old grommets (2) from cylinder body (1).
Brake Master Cylinder - Removal8 steps
△ CAUTION
The vacuum in the power brake booster must be depleted before removing the master cylinder to avoid damaging the master cylinder and to prevent inhalation of the o-ring or any other contamination into the booster. The preferred method is to pump the brake pedal while the engine is not running until the brake pedal becomes firm. An alternative method is to remove and immediately reinstall the check valve located on the booster. If the check valve is removed, special care should be taken to ensure that the grommet is not damaged and remains seated, the check valve is dry and free of debris, and that contaminates cannot be ingested during removal.
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  1. With the engine off, depress the brake pedal five times to deplete any vacuum that may remain in the booster unit.
  2. Siphon and drain the fluid from the reservoir (2).
  3. Disconnect the fluid level electrical connector (3) from the reservoir (2).
  4. Remove the brake lines (4) at the master cylinder.
  5. Remove mounting nuts (5) from the master cylinder.
  6. Remove master cylinder.
  7. Remove cylinder cover and drain the rest of the fluid.
  8. If master cylinder reservoir requires service, Brake Master Cylinder Reservoir - Removal.
Brake Master Cylinder Reservoir - Installation7 steps
△ CAUTION
Do not use any type of tool to install the grommets (2). Tools may cut, or tear the grommets creating a leak problem after installation. Install the grommets using finger pressure only and insure that the grommets are properly seated and checked for leaks after installation.
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  1. Lubricate new grommets (2) with clean brake fluid and Install new grommets (2) onto reservoir outlets (1). Use finger pressure to install and seat grommets.
  2. Start reservoir (1) and grommets into holes on master cylinder.
  3. Then rock reservoir (1) back and forth while pressing downward to seat it in the holes on the master cylinder. Make sure the four tabs are securely seated over the nubs (3).
  4. Install the fluid level sensor (2) if removed by just inserting the sensor in the reservoir until the tabs click.
  5. Reconnect the electrical connector (3) to the fluid reservoir level switch.
  6. Remove the prop rod from the vehicle.
  7. Fill and bleed base brake system, Service and Repair.
Brake Master Cylinder - Installation6 steps
ℹ NOTE
If master cylinder is replaced, bleed cylinder before installation.
ℹ NOTE
Insure the O-ring is on the master cylinder at the booster interface.
Fig. 1
Fig. 1
Fig. 2
Fig. 2
  1. Clean cylinder mounting surface of brake booster (3).
  2. Install master cylinder onto brake booster studs (4).
  3. Install mounting nuts (5) and tighten to 17 Nm (151 in. lbs.).
  4. Connect the brake lines (4) to the master cylinder and tighten to 19 Nm (168 in. lbs.).
  5. Connect fluid level electrical connector (3) to the reservoir (2).
  6. Fill and bleed base brake system, Service and Repair.
Brake Master Cylinder: Testing and Inspection15 steps
  1. Start the engine and check the booster vacuum hose connections. A hissing noise indicates a vacuum leak. Correct any vacuum leaks before proceeding.
  2. Stop the engine and pump the brake pedal until all vacuum reserve in the booster is depleted.
  3. Press and hold the brake pedal under light foot pressure. The pedal should hold firm. If the pedal falls away, there may be an external leak or the master cylinder is faulty (internal leakage).
  4. Start the engine and note pedal action. It should fall away slightly under light foot pressure, then hold firm. If no pedal action is discernible, the power booster, vacuum supply or vacuum check valve is faulty, proceed to the POWER BOOSTER VACUUM TEST.
  5. If the POWER BOOSTER VACUUM TEST passes, rebuild the booster vacuum reserve as follows: Release the brake pedal. Increase engine speed to 1500 RPM, close the throttle and immediately turn off the ignition to stop the engine.
  6. Wait a minimum of 90 seconds and try brake action again. The booster should provide two or more vacuum assisted pedal applications. If the vacuum assist is not provided, the booster is faulty. POWER BOOSTER VACUUM TEST
  7. Connect a vacuum gauge to the booster check valve with a short length of hose and T-fitting.
  8. Start and run the engine at curb idle for one minute.
  9. Observe the vacuum supply. If the vacuum supply is less that 12 inches HG (406 millibars), repair the vacuum supply.
  10. Clamp the hose shut between the intake vacuum source and the check valve.
  11. Stop the engine and observe the vacuum gauge.
  12. If the vacuum drops more than one inch HG (33 millibars) within 15 seconds, the booster diaphragm or check valve is faulty. POWER BOOSTER CHECK VALVE TEST
  13. Remove the power booster check valve from the power booster.
  14. Using a hand operated vacuum pump, apply 15-20 inches HG (508-677 millibars) vacuum at the booster side of the check valve.
  15. The vacuum should hold steady. If the gauge on the pump indicates vacuum loss, the check valve is faulty and should be replaced.
Factory service manual
From the 2008 KK factory manual — descriptions, specs, torque & procedures for this part.
MASTER CYLINDER
The master cylinder has a removable plastic reservoir. The cylinder body is made of aluminum and contains a primary and secondary piston assembly. The cylinder body including the piston assemblies are not serviceable. If diagnosis indicates an internal problem with the cylinder body, it must be replaced as an assembly. The reservoir and grommets are the only replaceable parts on the master cylinder.
MASTER CYLINDER
The master cylinder bore contains a primary and secondary piston. The primary piston supplies hydraulic pressure to the front brakes. The secondary piston supplies hydraulic pressure to the rear brakes. The master cylinder reservoir stores reserve brake fluid for the hydraulic brake circuits.
MASTER CYLINDER/POWER BOOSTER
1. Start engine and check booster vacuum hose connections. A hissing noise indicates vacuum leak. Correct any vacuum leak before proceeding, also ensure booster mounting nuts are torqued correctly. 2. Stop engine and shift transmission into Neutral. 3. Pump brake pedal until all vacuum reserve in booster is depleted. 4. Press and hold brake pedal under light foot pressure. The pedal should hold firm, if the pedal falls away master cylinder is faulty (internal leakage). This could also indicate an external leak, such as at fittings, hoses, HCU, etc, or a symptom of an internal leak in the HCU
5. Start engine and note pedal action. It should fall away slightly under light foot pressure then hold firm. If no pedal action is discernible, power booster, vacuum supply, or vacuum check valve is faulty. Proceed to
the POWER BOOSTER VACUUM TEST.
6. If the POWER BOOSTER VACUUM TEST passes, rebuild booster vacuum reserve as follows: Release brake pedal. Increase engine speed to 1500 RPM, close the throttle and immediately turn off ignition to stop engine. 7. Wait a minimum of 90 seconds and try brake action again. Booster should provide two or more vacuum assisted pedal applications. If vacuum assist is not provided, booster is faulty.
POWER BOOSTER VACUUM TEST
1.   Connect vacuum gauge to booster check valve with short length of hose and T-fitting. See Fig. 49.
 2.   Start and run engine at curb idle speed for one minute.
 3.   Observe the vacuum supply. If vacuum supply is not adequate, repair vacuum supply.
 4.   Clamp hose shut between vacuum source and check valve.
 5.   Stop engine and observe vacuum gauge.
 6.   If vacuum drops more than one inch Hg (33 millibars) within 15 seconds, booster diaphragm or check
valve is faulty.
1 - TEE FITTING 2 - SHORT CONNECTING HOSE 3 - CHECK VALVE 4 - CHECK VALVE HOSE 5 - CLAMP TOOL 6 - INTAKE MANIFOLD 7 - VACUUM GAUGE
POWER BOOSTER CHECK VALVE TEST📷 1
1.   Disconnect vacuum hose from check valve.
  2.   Remove check valve and valve seal from booster.
  3.   Use a hand operated vacuum pump for test.
  4.   Apply 15-20 inches vacuum at large end of check valve. See Fig. 50.
  5.   Vacuum should hold steady. If gauge on pump indicates vacuum loss, check valve is faulty and should be
replaced.
1 - BOOSTER CHECK VALVE 2 - APPLY TEST VACUUM HERE 3 - VALVE SEAL
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MASTER CYLINDER BLEEDING📷 1
A new master cylinder should be bled before installation on the vehicle. Required bleeding tools include bleed
tubes and a wood dowel to stroke the pistons. Bleed tubes can be fabricated from brake line.
  1.   Mount master cylinder in vise.
  2.   Attach bleed tubes to cylinder outlet ports. Then position each tube end into reservoir. See Fig. 61.
  3.   Fill reservoir with fresh brake fluid.
  4.   Press cylinder pistons inward with wood dowel. Then release pistons and allow them to return under
spring pressure. Continue bleeding operations until air bubbles are no longer visible in fluid.
1 - BLEEDING TUBES 2 - RESERVOIR
figure
MASTER CYLINDER📷 3
Check Valve
  1.   Siphon and drain the fluid from the reservoir (2).
  2.   Disconnect the fluid level electrical connector (3) from the reservoir (2).
  3.   Remove the brake lines (4) at the master cylinder.
  4.   Remove mounting nuts (5) from the master cylinder.
5. Remove master cylinder. 6. Remove cylinder cover and drain the rest of the fluid. 7. If master cylinder reservoir requires service, see REMOVAL.
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MASTER CYLINDER📷 2
NOTE: If master cylinder is replaced, bleed cylinder before installation.
1. Clean cylinder mounting surface of brake booster (3).
NOTE: Insure the O-ring is on the master cylinder at the booster interface.
2. Install master cylinder onto brake booster studs (4).
Booster Check Valve
  3.   Install mounting nuts (5) and tighten to 17 N.m (151 in. lbs.).
  4.   Connect the brake lines (4) to the master cylinder and tighten to 19 N.m (168 in. lbs.).
  5.   Connect fluid level electrical connector (3) to the reservoir (2).
  6.   Fill and bleed base brake system. See STANDARD PROCEDURE.
FLUID
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RESERVOIR📷 4
Check Valve
1. Install prop rod on brake pedal to keep pressure on the brake system. 2. Remove reservoir cap and siphon fluid into drain container. 3. Remove the electrical connector (3) from the fluid level switch in the reservoir (2).
4. Remove the reservoir (1) from the master cylinder by pulling the four tabs (3) outward to release.
5. Remove the reservoir (1) from the master cylinder by pulling upwards. 6. If replacing the reservoir (1) remove the fluid level sensor (2) by squeezing the tabs together while pulling on the sensor (2).
7. Remove old grommets (2) from cylinder body (1).
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RESERVOIR📷 4
CAUTION: Do not use any type of tool to install the grommets (2). Tools may cut, or tear the grommets creating a leak problem after installation. Install the grommets using finger pressure only and insure that the grommets are properly seated and checked for leaks after installation.
1. Lubricate new grommets (2) with clean brake fluid and Install new grommets (2) onto reservoir outlets (1). Use finger pressure to install and seat grommets.
2. Start reservoir (1) and grommets into holes on master cylinder.
3. Then rock reservoir (1) back and forth while pressing downward to seat it in the holes on the master cylinder. Make sure the four tabs are securely seated over the nubs (3).
4. Install the fluid level sensor (2) if removed by just inserting the sensor in the reservoir until the tabs click.
Booster Check Valve
5. Reconnect the electrical connector (3) to the fluid reservoir level switch. 6. Remove the prop rod from the vehicle. 7. Fill and bleed base brake system. See STANDARD PROCEDURE.
SUPPORT PLATE
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