Dodge Nitro. Manual - part 365

Fig. 50: Power Brake Booster Cut Away 
Courtesy of CHRYSLER LLC 

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

 

2007 Dodge Nitro R/T 

2007 BRAKES Base - Service Information - Nitro

  

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. 50. 

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. 

DIAGNOSIS AND TESTING 

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. 51. 

8 - SECONDARY PUSH ROD (TO MASTER CYLINDER)
9 - SPRING
10 - MASTER CYLINDER MOUNTING STUDS

 

2007 Dodge Nitro R/T 

2007 BRAKES Base - Service Information - Nitro

  

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.  

Fig. 51: Typical Booster Vacuum Test Connections 
Courtesy of CHRYSLER LLC 

 

2007 Dodge Nitro R/T 

2007 BRAKES Base - Service Information - Nitro

  

POWER BOOSTER CHECK VALVE TEST 

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. 52.  

5. Vacuum should hold steady. If gauge on pump indicates vacuum loss, check valve is faulty and should be 

replaced.  

Fig. 52: Typical - Vacuum Check Valve & Seal

1 - TEE FITTING
2 - SHORT CONNECTING HOSE
3 - CHECK VALVE
4 - CHECK VALVE HOSE
5 - CLAMP TOOL
6 - INTAKE MANIFOLD
7 - VACUUM GAUGE

 

2007 Dodge Nitro R/T 

2007 BRAKES Base - Service Information - Nitro