Hydraulic - Trouble Shooting Guide

Hard Brake Pedal
• Check for engine vacuum, make sure manifold is open and clear of carbon build up. • Use a vacuum gauge to check the vacuum at the booster. Do not guess.
• Check vacuum hoses for soft spots, deterioration or collapse
_(replace hose if in doubt).
• Check brake pedal for binding.
• Check the condition of the foundation brakes - drums, linings,
_brake shoes for binding.
• Check air in hydraulic system.
• Check for any line restrictions.

Pedal Kickback
• Check for dirt or foreign matter in hydraulic system.
• Before replacing the booster, remove the master cylinder to clean out any dirt.
• Clean out the rest of the hydraulic system also.

Brake Will Not Release
• Be sure a brake booster with residual check valve is not used with
_master cylinder with check valve.
• On remote mounted boosters, disconnect the line between the master cylinder
_and the brake booster.
• If the brakes release, the trouble is in the Master Cylinder
_(possibly the brake pedal is binding).
• If brakes do not release, disconnect the line from the booster to the wheel _cylinders.
• If the brakes release, the problem will be in the booster.
• If the brakes still do not release, the problem is in the foundation brakes.
• If the brakes will not release on firewall mounted brake booster, disconnect the _hydraulic line to the wheels.
• If the brakes release, the problem is in the booster or master cylinder
_(Be sure the brake pedal is not binding).

Low Brake Pedal Make sure master cylinder reservoir is full.
• Check for air in the hydraulic system.
• Make sure there are no leaks in the wheel cylinders, lines or fittings.
• Check the foundation brakes for proper adjustment, cracked or over-sized drums.

SPECIAL NOTES
Common Booster Failure Causes

Gas Engines:
Gas is the cause of a large number of booster failures. If the vacuum hose does not have a vacuum check valve in the line, raw gas or gas fumes are drawn into the Hydrovac causing the diaphragm to rupture and fail. It could possibly cause an explosion. The vacuum hose should run from the manifold to the vacuum check valve mounted on the firewall above the carburetor, then down to the booster. If no firewall is available, such as on cab-over models, the vacuum hose should be routed so that it goes above the manifold and the down to the booster.

Propane and Butane Equipped Engines:
A vacuum check valve should be used as close to the manifold as possible and as high on the firewall as possible. This would prevent raw gas or fumes from getting to the Hydrovac or booster and prevent a possible explosion if the engine should backfire. A vacuum tank should be used between the engine and Hydrovac or booster when butane or propane gas is used to fuel the engine.

Diesel Engines:
Diesel engines with vacuum pumps need a check valve in the vacuum line to prevent oil from being drawn into the booster when the engine is shut down. Oil will ruin the diaphragm causing the booster to fail.

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