What is a Hydro-Boost?

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Hydro-Boost was first introduced back in 1973. Hydro-Boost uses hydraulic pressure generated by the facility steering pump instead of an engine vacuum to produce power-assisted braking.

Inside the Hydro-Boost unit, which inserts between the hydraulic brake cylinder and treadle, is a spool valve and piston assembly. When the driving force steps on the foot lever, the pushrod slides forward and changes the position of the spool valve. This opens a valve port that routes power-assisted steering fluid into the cavity behind the piston to push it forward and apply the brakes.

Hydro-Boost also uses an “accumulator” to store pressure. Some accumulators are nitrogen pressurized while others are spring-loaded, counting on the appliance. The accumulator provides backup pressure just in case normal hydraulic pressure is lost (because the engine stalls or the ability steering pump drive belt breaks). There’s usually enough reserve pressure within the accumulator for 1 to three power-assisted stops.



Problems with this technique will be caused by spool valve or piston wear inside the Hydro-Boost unit, fluid leaks or loss of pressure thanks to a worn steering mechanism pump, slipping pump belt, or low power-assisted steering fluid level. Slow foot lever return is also caused by excessive seal friction inside the booster, faulty spool action, or a restriction within the return line to the pump.


Grabby Brakes:

Grabby brakes are probably the result of contamination inside the system or a broken spool return spring. If the brakes apply by themselves with no pedal effort, the system may have restricted return flow or a defunct dump valve. The excessive pedal effort is caused by internal leakage or the seeping of fluid past the accumulator/booster seal.

A simple thanks to testing the Hydro-Boost system is to pump the brakes five or sixfold with the engine off to discharge the accumulator. Then displace hard on the pedal (about 40 lbs. of force) and begin the engine. sort of a vacuum booster, you must feel the pedal fall slightly, then rise when the engine starts.

If a braking problem seems to be within the booster, the booster will get replaced. Warning: The Hydro-Boost accumulator must be fully depressurized by pumping the foot pedal a dozen times before any hydraulic lines are opened or the booster is disconnected.

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