Weak or No Booster Assist Due to Vac Hose Problems

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Arnold Harmon
5 years ago
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Weak or No Booster Assist Due to Vac Hose Problems All vehicles equipped with vacuum brake boosters. Weak or no power assist. Insufficient vacuum volume to operate booster at maximum efficiency.

1 Weak or No Booster Assist Due to Vac Hose Problems All vehicles equipped with vacuum brake boosters. Weak or no power assist. Insufficient vacuum volume to operate booster at maximum efficiency. Check vacuum draw available with a gauge connected between engine and booster. At idle, healthy engines draw somewhere between 17 and 22 in Hg. Check vacuum by depressing brake pedal firmly until it stops. The gauge should read a drop to approximately 10 in. Hg and then quickly recover to a normal reading. If vacuum takes too long to recover, there is a restriction in the volume, i.e.: fitting clogged or vacuum hose collapsed. Repair as necessary. While a defective booster will cause a hard pedal, a spongy or low pedal requires a hydraulic system check. JDA5245 PT

2 A Filter In Line, Saves Time All gasoline vehicles with vacuum power brake boosters. Premature Booster failure; improper operation. Gasoline, gas fumes, or moisture have entered the booster damaging internal rubber components. Remove vacuum line from booster and check vacuum hose for gas odor. If present, the source of gas MUST be eliminated before replacing booster. Check the operation of in-line check valves, vacuum vent valves or delay valves. Replace as necessary. Check vacuum hose routing. Do not eliminate any loops in the line because they function as moisture and vapor traps. Replace the in-line charcoal filter and position exactly as the original. If not filter equipped, installation of an aftermarket filter is recommended. Check PCV system. Replace valve or repair system as necessary. Check for leaking injectors or carburetor. Improper operation could cause an excessive rich condition. EXAMPLE OF IN-LINE FILTER AND HOSE LOOP JD5227 PT

Rich-Running Fuel Injected Engine Causes Booster Failure All vehicles with gasoline fuel injected engines and vacuum boosters.

A rich-running engine due to improper fuel management causes excess gas or gasoline fumes to enter booster, thus destroying the diaphragm.

Check the old booster for gasoline odor. If it smells like gas DO NOT install the replacement unit until the problem is corrected.

3 Rich-Running Fuel Injected Engine Causes Booster Failure All vehicles with gasoline fuel injected engines and vacuum boosters. Booster failure due to ruptured diaphragm (hard pedal, no assist). A rich-running engine due to improper fuel management causes excess gas or gasoline fumes to enter booster, thus destroying the diaphragm. Ensure proper operation of fuel management system. Check for defective injectors, high fuel pressure, leaking fuel pressure regulator and proper ECM operation. Check the old booster for gasoline odor. If it smells like gas DO NOT install the replacement unit until the problem is corrected. Typical vacuum booster diaphragm failure due to gas or gasoline fumes Another cause of diaphragm failure is master cylinder brake fluid entering the booster due to a faulty intermediate pushrod seal in the booster. If brake fluid is found between master cylinder and booster, the booster will have to be replaced (see ProTech PT ). JDA5244 PT

Wrong Pedal Rod or Brake Light Switch Adjustment Problem? All vehicles with firewall-mounted brake boosters. Brake light stays on, as if the pedal rod is too short on the replacement unit.

Finally, inspect the switch and pedal rod and adjust if possible Verifying the application and unit: Check the vehicle information using the VIN and registration if available.

Many vacuum and hydroboost units have a code number stamped or molded on the flattened end of the pedal rod or on the shaft between the boot and the end of the shaft.

4 Wrong Pedal Rod or Brake Light Switch Adjustment Problem? All vehicles with firewall-mounted brake boosters. Brake light stays on, as if the pedal rod is too short on the replacement unit. Possible misadjusted brake pedal rod, misadjusted brake light switch, or the wrong unit. First, verify the application and the unit ordered. Next, verify the unit received is correct. Finally, inspect the switch and pedal rod and adjust if possible Verifying the application and unit: Check the vehicle information using the VIN and registration if available. Look for a pedal rod number on original unit. Many vacuum and hydroboost units have a code number stamped or molded on the flattened end of the pedal rod or on the shaft between the boot and the end of the shaft. The code can be any combination of letters or numbers from one to five digits. Compare the codes found on both the original and replacement units, in most case they will match. Please refer to the Pedal Rod ID chart in our Brake Booster catalog for the complete list of cross-reference codes and unit part numbers. Adjust the pedal rod or switch: Refer to the vehicle service manual for installation and adjustment procedures that may apply to the application. Some boosters may appear to have no adjustment or only a single adjustment. However in some vehicles, such as Hondas and Acuras, their pedal rods have two adjustments, one of which is not readily apparent. Please refer to ProTech PT for more details. If the rod itself isn t adjustable, the brake light switch probably is. A 1999 Chrysler 300M is a good example the adjustment procedure is outlined below. For your application, please check the vehicle service manual for possible adjustment procedures. Brake Light Switch Adjustment: 1999 Chrysler 300M 1. Remove stop lamp switch from its bracket by rotating it approximately 30 in a counter-clockwise direction. 2. Disconnect wiring harness connector from stop lamp switch. 3. Hold stop lamp switch firmly in one hand. Then using the other hand, pull outward on the plunger of the stop lamp switch until it has ratcheted out to its fully extended position. 4. Install the stop lamp switch into the bracket using the following procedure. Depress the brake pedal as far down as possible. Then while keeping the brake pedal depressed, install the stop lamp switch into the bracket by aligning the index key on the switch with slot at the top of the square hole in the mounting bracket. When the switch is fully installed in the square hole of the bracket, rotate switch clockwise approximately 30 to lock the switch into the bracket. 5. Connect the wiring harness connector to the stop lamp switch. 6. Gently pull back on brake pedal until the pedal stops moving. This will cause the switch plunger to ratchet backward to the correct position. CAUTION: Do not use excessive force when pulling back on brake pedal to adjust the stop lamp switch. If too much force is used, damage to the vacuum booster, stop lamp switch or striker can result. Procedure complete. 7. Finish installation following service manual and any supplied installation instructions. This ProTech bulletin is supplied as technical information only and is not an authorization for repair. JDB1143 PT

5 Failed Booster Seal Causes Master Cylinder Leaks Vehicles equipped with power brake booster assemblies. Chronic master cylinder failure due to fluid leaking past secondary seal in the master cylinder bore. A defective master cylinder pushrod seal in the power brake booster allowing vacuum to draw fluid past secondary seal of the master cylinder. Replace both master cylinder and power brake unit. MASTER CYLINDER PUSH ROD PUSH ROD SEAL PRIMARY PISTON SECONDARY SEAL FLUID LEAK When replacing brake components, always flush entire brake system with approved brake fluid from a sealed container. JDA3120 PT

Angle Mounted Master Cylinder Bleeding Procedure

Angle Mounted Master Cylinder Bleeding Procedure All angle-mounted master cylinders. Unable to obtain a firm brake pedal when bleeding master cylinder on vehicle Cause: Air trapped in the upper end of