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Vacuum Brake Booster

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

Parts

PartBrake Booster
ManufacturerCHY
OEM part #68039279AC
Price$112.00

Labor

Replace2.0 hr
Warranty 1.7 hrSkill B
Procedures
Power Brake Booster - Installation15 steps
ℹ NOTE
Lubricate the pedal pin with Mopar multi-mileage grease before installation.
△ CAUTION
Do not reuse the original stop lamp switch. Anytime a switch has been removed or its position compromised, a new switch must be installed and adjusted. Do not attempt to readjust the switch.
Fig. 1
Fig. 1
Fig. 2
Fig. 2
  1. Align and position booster on the dash panel.
  2. Install booster mounting nuts (1). Tighten nuts just enough to hold booster in place.
  3. Slide booster push rod onto the brake pedal (2). Then secure push rod to pedal pin with retaining clip (3).
  4. Tighten booster mounting nuts (1) to 25 Nm (220 in. lbs.).
  5. Install and adjust a NEW stop lamp switch. Stop Lamp Switch - Installation
  6. Install the knee blocker, Kneeblocker - Installation.
  7. If original master cylinder is being installed, check condition of seal at rear of master cylinder. Replace seal if cut, or torn.
  8. Clean cylinder mounting surface of brake booster. Use shop towel wetted with brake cleaner for this purpose. Dirt, grease, or similar materials will prevent proper cylinder seating and could result in vacuum leak.
  9. Align and install master cylinder on the booster studs. Install mounting nuts and tighten to 25 Nm (220 in. lbs.).
  10. Connect vacuum hose to booster check valve (1).
  11. Remount the HCU. Tighten bracket mounting nuts to 14 Nm (125 in. lbs.).
  12. Connect and secure the brake lines (4) to HCU or junction block and master cylinder. Start all brake line fittings by hand to avoid cross threading.
  13. Connect the wire to fluid level switch (3) at the bottom of the reservoir (2).
  14. Fill and bleed base brake system, Service and Repair.
  15. Verify proper brake operation before moving vehicle.
Power Brake Booster - Removal - RHD10 steps
Fig. 1
Fig. 1
Fig. 2
Fig. 2
  1. Remove the air box Air Cleaner - Removal.
  2. Siphon the fluid out of the master cylinder.
  3. Remove the brake lines from the master cylinder.
  4. Remove the master cylinder Brake Master Cylinder - Removal.
  5. Disconnect vacuum hose from booster check valve (1).
  6. Remove knee blocker under the steering column, Kneeblocker - Removal.
  7. Remove the brake lamp switch and discard it. Do not reuse the stop lamp switch.Stop Lamp Switch - Removal
  8. Remove retaining clip (3) that secures booster push rod to brake pedal (2).
  9. Remove nuts (1) attaching booster to the dash panel.
  10. In engine compartment, slide booster studs out of dash panel, tilt booster upward, and remove booster from engine compartment.
Power Brake Booster - Removal10 steps
Fig. 1
Fig. 1
Fig. 2
Fig. 2
  1. Disconnect the wire (3) to the fluid level switch at the bottom of the reservoir (2).
  2. Remove the master cylinder (2) Brake Master Cylinder - Removal.
  3. Disconnect vacuum hoses from booster check valve (1).
  4. Remove the brake lines (4) from the master cylinder and the HCU (ABS vehicles only) or the junction block for clearance.
  5. Disconnect the HCU from the mounts and move to the side for clearance of the booster.
  6. Remove knee blocker under the steering column, Kneeblocker - Removal.
  7. Remove the brake lamp switch and discard it. Do not reuse the stop lamp switch.Stop Lamp Switch - Removal
  8. Remove retaining clip (3) that secures booster push rod to brake pedal (2).
  9. Remove nuts attaching booster (1) to the dash panel.
  10. In engine compartment, slide booster studs out of dash panel, tilt booster upward, and remove booster from engine compartment.
Power Brake Booster - Installation - RHD15 steps
ℹ NOTE
Lubricate the pedal pin with Mopar multi-mileage grease before installation.
△ CAUTION
Do not reuse the original stop lamp switch. Anytime a switch has been removed or its position compromised, a new switch must be installed and adjusted. Do not attempt to readjust the switch.
Fig. 1
Fig. 1
Fig. 2
Fig. 2
  1. Align and position booster on the dash panel.
  2. Install booster mounting nuts (1). Tighten nuts just enough to hold booster in place.
  3. Slide booster push rod onto the brake pedal (2). Then secure push rod to pedal pin with retaining clip (3).
  4. Tighten booster mounting nuts (1) to 39 Nm (29 ft. lbs.).
  5. Install and adjust a NEW stop lamp switch. Stop Lamp Switch - Installation.
  6. Install the knee blocker, Kneeblocker - Installation.
  7. If original master cylinder is being installed, check condition of seal at rear of master cylinder. Replace seal if cut, or torn.
  8. Clean cylinder mounting surface of brake booster. Use shop towel wetted with brake cleaner for this purpose. Dirt, grease, or similar materials will prevent proper cylinder seating and could result in vacuum leak.
  9. Align and install master cylinder on the booster studs (2). Install mounting nuts and tighten to 17.5 Nm (155 in. lbs.) Brake Master Cylinder - Installation.
  10. Connect vacuum hose to booster check valve (1).
  11. Connect and secure the brake lines to master cylinder. Start all brake line fittings by hand to avoid cross threading.
  12. Connect the wire to fluid reservoir.
  13. Install the air box.
  14. Fill and bleed base brake system, Service and Repair.
  15. Verify proper brake operation before moving vehicle.
Vacuum Brake Booster: 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.
Power Brake Booster - Descriptionreference
Fig. 1
Fig. 1
DESCRIPTION The booster assembly consists of a housing divided into separate chambers by two internal diaphragms. The outer edge of each diaphragm is attached to the booster housing. The diaphragms are connected to the booster primary push rod. Two push rods are used in the booster. The primary push rod connects the booster to the brake pedal. The secondary push rod connects the booster (2) to the master cylinder (1) to stroke the cylinder pistons. The booster assembly is of the tie-bar design. This means the structural support of the assembly is through the tie-bars, whose ends protrude through the booster shell. One end is the master cylinder mounting stud and the other end is the booster mounting stud. The booster assembly (with properly functioning check valve installed) may not have a good vacuum seal unless the booster is installed on the dash panel mounting bracket with master cylinder and booster mounting nuts properly torqued.
Power Brake Booster - Operationreference
Fig. 1
Fig. 1
Fig. 2
Fig. 2
OPERATION The atmospheric inlet valve is opened and closed by the primary push rod (6). Booster vacuum supply is through a hose attached to an intake manifold fitting at one end and to the booster check valve (1) at the other. The vacuum check valve (1) in the booster housing (4) is a one-way device that prevents vacuum leak back. Power assist is generated by utilizing the pressure differential between normal atmospheric pressure and a vacuum. The vacuum needed for booster operation is taken directly from the engine intake manifold. The entry point for atmospheric pressure is through a filter and inlet valve at the rear of the housing (Figure 1). The chamber areas forward of the booster diaphragms are exposed to vacuum from the intake manifold. The chamber areas to the rear of the diaphragms, are exposed to normal atmospheric pressure of 101.3 kilopascals (14.7 pounds/square in.). Brake pedal application causes the primary push rod to open the atmospheric inlet valve. This exposes the area behind the diaphragms to atmospheric pressure. The resulting pressure differential provides the extra apply force for power assist. The booster check valve, check valve grommet and booster seals are serviceable.
Factory service manual
From the 2008 KK factory manual — descriptions, specs, torque & procedures for this part.
POWER BRAKE BOOSTER📷 1
The booster assembly consists of a housing divided into separate chambers by two internal diaphragms. The outer edge of each diaphragm is attached to the booster housing. The diaphragms are connected to the booster primary push rod.
Two push rods are used in the booster. The primary push rod connects the booster to the brake pedal. The secondary push rod connects the booster (2) to the master cylinder (1) to stroke the cylinder pistons.
The booster assembly is of the tie-bar design. This means the structural support of the assembly is through the tie-bars, whose ends protrude through the booster shell. One end is the master cylinder mounting stud and the other end is the booster mounting stud. The booster assembly (with properly functioning check valve installed) may not have a good vacuum seal unless the booster is installed on the dash panel mounting bracket with master cylinder and booster mounting nuts properly torqued.
figure
POWER BRAKE BOOSTER📷 2
1 - VACUUM CHECK VALVE 2 - FRONT DIAPHRAGM 3 - REAR DIAPHRAGM 4 - HOUSING 5 - SEAL 6 - PRIMARY PUSH ROD (TO BRAKE PEDAL) 7 - BOOSTER MOUNTING STUDS
8 - SECONDARY PUSH ROD (TO MASTER CYLINDER) 9 - SPRING 10 - MASTER CYLINDER MOUNTING STUDS
The atmospheric inlet valve is opened and closed by the primary push rod (6). Booster vacuum supply is through a hose attached to an intake manifold fitting at one end and to the booster check valve (1) at the other. The vacuum check valve (1) in the booster housing (4) is a one-way device that prevents vacuum leak back.
Power assist is generated by utilizing the pressure differential between normal atmospheric pressure and a vacuum. The vacuum needed for booster operation is taken directly from the engine intake manifold. The entry point for atmospheric pressure is through a filter and inlet valve at the rear of the housing. See Fig. 48.
The chamber areas forward of the booster diaphragms are exposed to vacuum from the intake manifold. The chamber areas to the rear of the diaphragms, are exposed to normal atmospheric pressure of 101.3 Kilopascals (14.7 pounds/square in.).
Brake pedal application causes the primary push rod to open the atmospheric inlet valve. This exposes the area behind the diaphragms to atmospheric pressure. The resulting pressure differential provides the extra apply force for power assist.
The booster check valve, check valve grommet and booster seals are serviceable.
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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
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
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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
figure
POWER BRAKE BOOSTER - LHD📷 2
Check Valve
1. Disconnect the wire (3) to the fluid level switch at the bottom of the reservoir (2). 2. Remove the master cylinder (2). See REMOVAL. 3. Disconnect vacuum hoses from booster check valve (1). 4. Remove the brake lines (4) from the master cylinder and the HCU (ABS vehicles only) or the junction block for clearance. 5. Disconnect the HCU from the mounts and move to the side for clearance of the booster.
 6.   Remove knee blocker under the steering column. Refer to REMOVAL .
 7.   Remove the brake light switch and discard. Refer to REMOVAL .
 8.   Remove retaining clip (3) that secures booster push rod to brake pedal (2).
 9.   Remove nuts attaching booster (1) to the dash panel.
10.   In engine compartment, slide booster studs out of dash panel, tilt booster upward, and remove booster
from engine compartment.
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figure
POWER BRAKE BOOSTER - RHD📷 1
1. Remove the air box. Refer to REMOVAL . 2. Siphon the fluid out of the master cylinder.
3. Remove the brake lines from the master cylinder. 4. Remove the master cylinder. See REMOVAL. 5. Disconnect vacuum hose from booster check valve (1).
  6.   Remove knee blocker under the steering column. Refer to REMOVAL .
  7.   Remove the brake light switch and discard. Refer to REMOVAL .
  8.   Remove retaining clip (3) that secures booster push rod to brake pedal (2).
  9.   Remove nuts (1) attaching booster to the dash panel.
 10.   In engine compartment, slide booster studs out of dash panel, tilt booster upward, and remove booster
from engine compartment.
figure
POWER BRAKE BOOSTER - LHD📷 2
1. Align and position booster on the dash panel.
2. Install booster mounting nuts (1). Tighten nuts just enough to hold booster in place.
NOTE: Lubricate the pedal pin with Mopar multi-mileage grease before

Installation

3
Slide booster push rod onto the brake pedal (2). Then secure push rod to pedal pin with retaining clip (3).
4
Tighten booster mounting nuts (1) to 25 N.m (220 in. lbs.).
5
Install a new brake lamp switch and reconnect the electrical connector.
6
Install the knee blocker. Refer to INSTALLATION .
Booster Check Valve
7
If original master cylinder is being installed, check condition of seal at rear of master cylinder. Replace
seal if cut, or torn.
8
Clean cylinder mounting surface of brake booster. Use shop towel wetted with brake cleaner for this
purpose. Dirt, grease, or similar materials will prevent proper cylinder seating and could result in vacuum leak.
9
Align and install master cylinder on the booster studs. Install mounting nuts and tighten to 25 N.m (220
in. lbs.).
10
Connect vacuum hose to booster check valve (1).
11
Remount the HCU. Tighten bracket mounting nuts to 14 N.m (125 in. lbs.).
12
Connect and secure the brake lines (4) to HCU or junction block and master cylinder. Start all brake line
fittings by hand to avoid cross threading.
13
Connect the wire to fluid level switch (3) at the bottom of the reservoir (2).
14
Fill and bleed base brake system. See STANDARD PROCEDURE.
15
Verify proper brake operation before moving vehicle.
figure
figure
POWER BRAKE BOOSTER - RHD📷 3
1. Align and position booster on the dash panel. 2. Install booster mounting nuts (1). Tighten nuts just enough to hold booster in place.
NOTE: Lubricate the pedal pin with Mopar multi-mileage grease before

Installation

3
Slide booster push rod onto the brake pedal (2). Then secure push rod to pedal pin with retaining clip (3).
4
Tighten booster mounting nuts (1) to 39 N.m (29 ft. lbs.).
5
Install a new brake lamp switch and reconnect the electrical connector.
6
Install the knee blocker. Refer to INSTALLATION .
7
If original master cylinder is being installed, check condition of seal at rear of master cylinder. Replace
seal if cut, or torn.
8
Clean cylinder mounting surface of brake booster. Use shop towel wetted with brake cleaner for this
purpose. Dirt, grease, or similar materials will prevent proper cylinder seating and could result in vacuum leak.
9
Align and install master cylinder on the booster studs (2). Install mounting nuts and tighten to 17.5 N.m
(155 in. lbs.). See INSTALLATION.
10
Connect vacuum hose to booster check valve (1).
11
Connect and secure the brake lines to master cylinder. Start all brake line fittings by hand to avoid cross
threading.
12
Connect the wire to fluid reservoir.
13
Install the air box.
14
Fill and bleed base brake system. See STANDARD PROCEDURE.
15
Verify proper brake operation before moving vehicle.
MASTER CYLINDER
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