HYDROBOOST REBUILD?
Thread Starter
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Lead Driver
Joined: Mar 2008
Posts: 7,174
Likes: 377
From: Near Los Angeles
HYDROBOOST REBUILD?
I'm having some probs with my hydroboost. Some members have been kind enough to post links that might be helpful. Thanks. However, I am still looking for detailed info. about how to rebuild one of these things. For me it is Pandora's box. I want to be prepared before hand.
If some could point me in the right direction to find out how to rebuild one of these, I would appreciate it.
If some could point me in the right direction to find out how to rebuild one of these, I would appreciate it.
Thread Starter
|
Lead Driver
Joined: Mar 2008
Posts: 7,174
Likes: 377
From: Near Los Angeles
So far this is the best info I have found on the H.B. And lo and behold, it does mention the hydroboost activating the brakes w/o pressure on the pedal!!!!!!!!!!
For helvede.
Operation, Diagnosis and Repair of HYDRO-BOOSTPower Assist Systems
Bill Williams, Technical Contributor
Hydro-boost power assist was introduced in 1973 by Bendix as an alternative to the vacuum booster.The hydro-boost uses the hydraulic pressure from the power steering system to provide the driver assist in applying the brakes. There are three reasons why a vehicle may be equipped with hydro-boost instead of a vacuum booster:1. The
r
is no vacuum source available, as in diesel engines, or the vacuum source available istoo weak to adequately supply a vacuum booster.2. There is limited space available for the power assist device.3. The vehicle requires more assist than is available froma vacuum booster.
Hydro-boost has been used on a variety of vehicles sinceits introduction and OEM applications presently include:
*
1996 and newer Cobras and all V8 Mustang;* Most 2500 and 3500 series GMC/Chevy trucks;* Dodge Ram equipped with Cummins turbo diesel;* Ford Super Duty series trucks equipped with Diesel; and* All Hummers - including the H2.Proper diagnosis of hydro-boost related problems requires an understanding of how the systemworks. A typical hydro-boost is shown in Figure 1. The hydro-boost is plumbed in line with the steeringgear. The power steering pump supplies pressurized fluid for both the power steering gear and hydro-boost.
Spool Valve
Fluid flow in and out of the hydro-boost is controlled by what is known asa spool valve. Spool valves are used in a variety of hydrauliccomponents, such as the valve body of an automatic transmission. Aspool valve is basically a hollow cylinder with a number of ringsmachined into it (see Figure 2). The surface of the spool valve is highlypolished to form a sealing surface. The raised portions of the cylinder are called lands while the indentations are called annular grooves.Figure 3 shows a simplified spool valve positioned in a bore with threeports. The path of the pressurized fluid from port 1 is determined by theposition of the spool valve. The spool valve is positioned in figure 4 to allow fluid flow from port 1 toport 2 while port 3 is blocked by land #1. Figure 4 shows the spool valve moved to the left whichchanges the fluid flow. The fluid flow is now from port 1 to port 3 with port 2 being blocked by land #2.The spool valve in a hydro-boost works in a similar fashion.
Hydro-boost Construction
Figure 5 shows a cutaway of a hydro-boost with all the major components labeled. These include the housing, power chamber, inputrod assembly, a lever assembly, a power piston, spool valve assemblyand an output rod. The housing is fitted with three ports as identified inFigure 6. The spool valve fits into a precisely machined bore that is partof the hydro-boost housing as shown in Figure 7. The fit between thespool valve and the bore is such that it creates a seal while at the sametime allowing enough fluid between the lands and bore to providelubrication. The spool valve's position is determined by the lever assembly which is connected to the input rod.
Pedal Unapplied
When the brakes are unapplied the spool valve is positioned as shown in Figure 8. In this position thepressurized fluid from the power steering pump is allowed to flow to the steering gear, but not into thepower chamber. The spool valve vents the power chamber to the return line of the power steeringpump reservoir.
Pedal Applied
Once the brake is applied, the input rod moves forward (left)to the power piston assembly. The piston return spring ispreventing the power piston and pin "A" from moving forward.This lack of movement causes the input rod to force the travellimiter valve assembly into the power piston which results inpin "B" moving forward. The lack of movement at pin "A" andforward movement of pin "B" causes the lever to pivot at pin"A". The top of the lever moves forward (left) which results inmoving the spool valve (See Figure 9).The forward movement of the spool valve closes the reservoir port which seals off the power chamber.Continued movement of the spool valve opens the pressure port from the power steering pumpallowing pressurized fluid into the power chamber while at the same time maintaining the fluid flow tothe steering gear. The pressure in the power chamber causes the power piston to move forward (left)which applies the brakes through the output rod (See Figure 10).
Pedal Released
Once the brakes are released, the spool valve return springpushes the spool valve back to its rest position. This vents thepressure in the power chamber to the power steering pumpreservoir through the return line. The power piston and lever assembly are returned to their rest position by return springswhich in turn brings the brake pedal back to an unappliedposition.
Back-Up
Similar to the vacuum booster, the hydro-boost is equippedwith a backup or reserve in case the source of pressurizedfluid is lost. A failure in the power steering system, such as abroken hose, broken power steering pump drive belt, or failed pump,would result in a loss of pressure to both the hydro-boost and steeringgear. The hydro-boost uses a high-pressure accumulator to store power steering fluid under pressure in the event of a failure. There are two typesof accumulators used, some hydro-boost units use an externalaccumulator, while others incorporate the accumulator in the power piston.The accumulator could be either of the spring-loaded variety or nitrogen-gas type.In the event of a loss of pressurized fluid, the accumulator will provide two to three power assistedstops. Upon the first application of the brakes after an engine stall or loss of power steering, you wouldfind approximately 60 to 75% of the normal assist available. If you were to release and apply thebrakes again, you would find approximately 30% to 40% assist, then again approximately 10% to20%, until you have depleted all stored reserve assist. Once you have depleted all of the storedpressure, the brakes will no longer have power assist and willbe manual in their operations.During normal operation, the accumulator is charged bypump pressure though a check valve assembly (See Figure11). The check valve allows fluid into the accumulator, butprevents it from escaping. When the pressure in the power chamber is lost due to a failure, the input rod linkage willoverride the power piston linkage and cause the check valveto be opened. The open check valve will release the storedfluid in the accumulator into the power chamber which willprovide the power assist.
Pedal Feel
The hydro-boost generates a different pedal feel than a vacuum booster. Basic function can bechecked by pumping the brake pedal until hard with the engine off and then starting the engine whilemaintaining slight pedal pressure. Proper operation should result in the brake pedal sinking down andthen pushing back up against your foot. The sinking of the pedal when the engine was started is aresult of the power chamber being pressurized. Once the power steering system is at full pressure, itresults in the pedal pushing back against your foot pressure.
Diagnosis
The hydro-boost requires a constant source of pressurizedpower steering fluid for proper operation. Problems in thepower steering system will be reflected in the operation of the hydro-boost.Accurate diagnosis of a hydro-boost power assist devicedepends on combining an understanding of their functionwith a logical diagnostic approach. Hydro-boost problemsusually break down into the following categories:* Noise problems; * Slow or incomplete pedal return; * Over sensitive braking; and * Self applying brakes Note: Each of these is covered in the following sections.
Noisy Booster
1. Confirm complaint making sure to note type of noiseand when it occurs. If the noise occurs during high brakepedal efforts or quick pedal release, go to step 2. If thenoise occurs during low brake pedal effort, engine idle - nopedal effort, or normal driving conditions, go to step 3.2. Noise occurs during high brake pedal efforts or quick pedalrelease: See normal operation noises listed below. Mostlikely the noises being heard are normal based on the typeof conditions.3. Operate the vehicle until the engine is at normal operatingtemperature. Duplicate the operating conditions above andlisten for the noise.4. Compare results with the normal noises listed under themore info section and with a known acceptable system.
Normal Operation Noises
Properly operating hydro-boost units will produce certain noises. These noises occur, for the most partwhen the brake pedal is manipulated in a manner not associated with everyday driving habits. Thegeneral categories of normal operating noises are (1) hissing noises and (2) clunk/clatter noises.The hydro-boost will emit normal hissing noises when above-normal brake pedal efforts are applied(40 lbs. and up). The hiss sounds particularly noticeable with the vehicle motionless and will increasein intensity as pedal pressure increases above 40 lbs. and system operating temperature increases.Loud hissing sounds at or below normal (20 to 25 lbs.) pedal effort warrants investigation.Clunk, clatter or clicking noises will be heard when the brake pedal is quickly released from hard (50to 100 lbs.) pedal efforts.
Slow or incomplete pedal return:
1. Run pump at fast idle.2. Pull the brake pedal rearward with approximately 10 lbs. force and release. Measure thedistance to the floorboard.3. Make 100-lb. brake application. Release brake pedal and measure distance to floorboard. Thebrake pedal should return to its normal position (step 2). If measurements are the same, go tostep 5.4. If the brake pedal does not return properly, check the pedal to be sure it is operating freely.Correct any sticking or binding as necessary.
5. If brakes are self applying and pedal is free, check for obstruction in the return line or a kinkedconnection between hydo-boost and pump reservoir. If obstruction or kink is found, go to step6, otherwise go to step 7.6. Remove obstruction or replace line as required. If condition remains, check for a damagedreaction end. If damaged the hydo-boost should be replaced or repaired.7. If brake pedal is free of any binding conditions and return line is free of obstructions, removethe master cylinder cover.8. Observe the brake fluid in the reservoir while rapidly depressing the brake pedal one inch.9. Fluid surface should have some movement or spout in the forward reservoir section. Minor spouting may occur in the rearward reservoir. If no movement or spouting of fluid occurs inforward reservoir, the hydro-boost unit is defective and must be replaced or repaired.Excessive pedal effort - brake pedal chatter - pulsation and/or leaks:
Perform Basic Test:
1. Engine (pump) off, depress and release the brake pedal four times to deplete all hydraulicpressure from hydo-boost.2. Depress brake pedal and hold with light pressure then start the engine. If the power section isoperating properly the pedal will fall slightly and then hold. Less pressure will be needed tohold the pedal in this position. If the power section is NOT operating, go to step 3, otherwisego to step 4.3. If power section is not operating properly, check pump reservoir level. If level is low, add fluidand repeat basic test plus Hydraulic Leak Test (Steps 4 to 5). If fluid level is good, go to step6.4. Steering Hydraulic Leak Test: Thoroughly clean the hydo-boost unit and all hose connections.Start the engine and run at idle speed. If the hose fittings do not leak go to step 5.5. Check the hydro-boost for leaks. Apply the brake pedal with approximately 100 lbs. force andhold while checking hydro-boost hose fittings for leaks. Do not hold brake pedal at 100 lbs.effort for more than five seconds at a time. If the hydo-boost leaks, it is defective and shouldbe replaced or repaired. If no leaks are found in the hydro-boost or hoses, do not repair or replace them.6. Fluid level good: Check tension and condition of drive belt. If the drive belt is loose or damaged, tighten or replace as required and repeat the basic test (Steps 1-2). If pump speedis slow, adjust and repeat basic test. If pump speed is OK, perform pump flow and relief pressure test.7. If pump output is below minimum specification, replace and repeat basic test. If all test andchecks are OK, the booster is defective and should be replaced or repaired.8. If power section is operating, perform the following steps in order.9. Hydro-boost accumulator pressure retention test: Run pump to medium speed, apply brakepedal force to 100 lbs. for not more than five seconds and then stop engine.10. Wait 90 seconds and apply the brakes. Two or more applications should be power assisted. If applications are not power assisted the hydro-boost is defective and should be replaced or repaired. If applications are power assisted, go to next step.11. Thoroughly clean the hydo-boost unit and all hose connections. Start the engine and run atidle speed. If the hose fittings do not leak, go to step 5.12. Check the hydro-boost for leaks. Apply the brake pedal with approximately 100lbs force andhold while checking hydro-boost hose fittings for leaks. Do not hold brake pedal at 100 lbs.effort for more than five seconds at a time. If the hydo-boost leaks, it is defective and shouldbe replaced or repaired. If no leaks are found in the hydro-boost or hoses, do not repair or replace them. Perform the brake hydraulic leak test.13. Brake Hydraulic Leak Test - Depress and release brake pedal several times, then hold pedaldepressed with medium pressure of 25 to 35lbs. If pedal does not fall away, hydraulic systemis not leaking. If pedal falls away, go to next step.14. Pedal falls away under constant pressure - hydraulic brake system is leaking. Check for external leaks at wheel cylinders, calipers, hoses and lines. If no leaks are found, additionaldiagnostic steps are necessary.
Service
The hydro-boost in not serviceable in the field. If the unit is not functioning properly, it must bereplaced. The replacement process is straight forward, but bleeding can sometimes be tricky. I amoffering a choice of techniques in this area. Hydro-boost brake systems are supposed to be self-bleeding, but this does not always prove to be true.
Bleed Technique 1:
1. Replace any hydraulic line showing external damage. Install new seals for all disconnectedfittings (as required) and install an in-line power steering filter. Tighten all hose fittings to OEspecifications.2. Flush the entire power steering system using the vehicle manufacturer's recommended fluid.Fill pump reservoir to the proper level.3. Disable engine to allow cranking without starting. Block wheels, put transmission in neutral or park and set parking brake, then crank engine 5 to 10 seconds (avoid overheating starter motor).4. Refill pump reservoir as necessary. Repeat step 3 until level is correct.5. Enable the engine to allow starting. Start engine and let idle. Slowly turn steering wheel fromlock-to-lock a number of times.6. Turn engine off and inspect fluid level and condition. Add or remove fluid as necessary. If fluidis foaming, wait one hour then recheck level. Repeat step 5 and 6 until fluid level is correctand shows no sign of air problem.NOTE: Many of you are aware that Ford power steering systems are very prone to air-relatedproblems. The most effective way to remove air in these systems is to apply a vacuum to the power steering pump reservoir. This technique can be used on most power steering systems.
Bleed Technique 2:
1. Remove return line from hydro-boost and plug end with appropriate size plug or bolt.2. Connect two- to three-foot piece of clear hose to return port on hydro-boost unit. Place end of hose into empty container at least 1 gallon in capacity.3. Fill power steering pump reservoir with correct fluid.4. Disable engine to allow cranking without starting. Block wheels, put transmission in neutral or park and set parking brake, then crank engine 5 to 10 seconds (avoid overheating starter motor) while applying and releasing brake pedal slowly.5. Refill pump reservoir as necessary. Repeat step 4 until no air is seen in return line from hydro-boost.6. Remove clear hose from return port and reconnect return line from pump.7. Enable the engine to allow starting. Start engine and let idle. Slowly turn steering wheel fromlock to lock a number of times.8. Turn engine off and inspect fluid level and condition. Add or remove fluid as necessary. If fluidis foaming, wait one hour then recheck level. Repeat step 7 and 8 until fluid level is correctand shows no sign of air problem.
Procedure
Use either of these bleeding procedures whenever replacing or servicing any component in a hydro-boost system. Normal driving conditions will remove air that remains trapped within the system whencomponents are properly installed and there are no flow restrictions in the system. Always refer to thevehicle service manual for specific installation and testing procedures.
Power Steering Flush
In addition to requiring the correct pressure, it is also critical that the fluid be clean. The tolerances inthe moving parts inside the hydro-boost are such that only a small amount of contaminates can causea malfunction. This is especially true of the spool valve. The tolerances necessary to form a metal-to-metal seal are quite small and any contaminates or tarnish buildup can prevent smooth operation of the spool valve. Since the spool valve controls the flow of fluid into and out of the power chamber, it iscritical it functions properly.Any vehicle equipped with a hydro-boost power assist will benefit from a periodic power steering flush.
For helvede.
Operation, Diagnosis and Repair of HYDRO-BOOSTPower Assist Systems
Bill Williams, Technical Contributor
Hydro-boost power assist was introduced in 1973 by Bendix as an alternative to the vacuum booster.The hydro-boost uses the hydraulic pressure from the power steering system to provide the driver assist in applying the brakes. There are three reasons why a vehicle may be equipped with hydro-boost instead of a vacuum booster:1. The
r
is no vacuum source available, as in diesel engines, or the vacuum source available istoo weak to adequately supply a vacuum booster.2. There is limited space available for the power assist device.3. The vehicle requires more assist than is available froma vacuum booster.
Hydro-boost has been used on a variety of vehicles sinceits introduction and OEM applications presently include:
*
1996 and newer Cobras and all V8 Mustang;* Most 2500 and 3500 series GMC/Chevy trucks;* Dodge Ram equipped with Cummins turbo diesel;* Ford Super Duty series trucks equipped with Diesel; and* All Hummers - including the H2.Proper diagnosis of hydro-boost related problems requires an understanding of how the systemworks. A typical hydro-boost is shown in Figure 1. The hydro-boost is plumbed in line with the steeringgear. The power steering pump supplies pressurized fluid for both the power steering gear and hydro-boost.
Spool Valve
Fluid flow in and out of the hydro-boost is controlled by what is known asa spool valve. Spool valves are used in a variety of hydrauliccomponents, such as the valve body of an automatic transmission. Aspool valve is basically a hollow cylinder with a number of ringsmachined into it (see Figure 2). The surface of the spool valve is highlypolished to form a sealing surface. The raised portions of the cylinder are called lands while the indentations are called annular grooves.Figure 3 shows a simplified spool valve positioned in a bore with threeports. The path of the pressurized fluid from port 1 is determined by theposition of the spool valve. The spool valve is positioned in figure 4 to allow fluid flow from port 1 toport 2 while port 3 is blocked by land #1. Figure 4 shows the spool valve moved to the left whichchanges the fluid flow. The fluid flow is now from port 1 to port 3 with port 2 being blocked by land #2.The spool valve in a hydro-boost works in a similar fashion.
Hydro-boost Construction
Figure 5 shows a cutaway of a hydro-boost with all the major components labeled. These include the housing, power chamber, inputrod assembly, a lever assembly, a power piston, spool valve assemblyand an output rod. The housing is fitted with three ports as identified inFigure 6. The spool valve fits into a precisely machined bore that is partof the hydro-boost housing as shown in Figure 7. The fit between thespool valve and the bore is such that it creates a seal while at the sametime allowing enough fluid between the lands and bore to providelubrication. The spool valve's position is determined by the lever assembly which is connected to the input rod.
Pedal Unapplied
When the brakes are unapplied the spool valve is positioned as shown in Figure 8. In this position thepressurized fluid from the power steering pump is allowed to flow to the steering gear, but not into thepower chamber. The spool valve vents the power chamber to the return line of the power steeringpump reservoir.
Pedal Applied
Once the brake is applied, the input rod moves forward (left)to the power piston assembly. The piston return spring ispreventing the power piston and pin "A" from moving forward.This lack of movement causes the input rod to force the travellimiter valve assembly into the power piston which results inpin "B" moving forward. The lack of movement at pin "A" andforward movement of pin "B" causes the lever to pivot at pin"A". The top of the lever moves forward (left) which results inmoving the spool valve (See Figure 9).The forward movement of the spool valve closes the reservoir port which seals off the power chamber.Continued movement of the spool valve opens the pressure port from the power steering pumpallowing pressurized fluid into the power chamber while at the same time maintaining the fluid flow tothe steering gear. The pressure in the power chamber causes the power piston to move forward (left)which applies the brakes through the output rod (See Figure 10).
Pedal Released
Once the brakes are released, the spool valve return springpushes the spool valve back to its rest position. This vents thepressure in the power chamber to the power steering pumpreservoir through the return line. The power piston and lever assembly are returned to their rest position by return springswhich in turn brings the brake pedal back to an unappliedposition.
Back-Up
Similar to the vacuum booster, the hydro-boost is equippedwith a backup or reserve in case the source of pressurizedfluid is lost. A failure in the power steering system, such as abroken hose, broken power steering pump drive belt, or failed pump,would result in a loss of pressure to both the hydro-boost and steeringgear. The hydro-boost uses a high-pressure accumulator to store power steering fluid under pressure in the event of a failure. There are two typesof accumulators used, some hydro-boost units use an externalaccumulator, while others incorporate the accumulator in the power piston.The accumulator could be either of the spring-loaded variety or nitrogen-gas type.In the event of a loss of pressurized fluid, the accumulator will provide two to three power assistedstops. Upon the first application of the brakes after an engine stall or loss of power steering, you wouldfind approximately 60 to 75% of the normal assist available. If you were to release and apply thebrakes again, you would find approximately 30% to 40% assist, then again approximately 10% to20%, until you have depleted all stored reserve assist. Once you have depleted all of the storedpressure, the brakes will no longer have power assist and willbe manual in their operations.During normal operation, the accumulator is charged bypump pressure though a check valve assembly (See Figure11). The check valve allows fluid into the accumulator, butprevents it from escaping. When the pressure in the power chamber is lost due to a failure, the input rod linkage willoverride the power piston linkage and cause the check valveto be opened. The open check valve will release the storedfluid in the accumulator into the power chamber which willprovide the power assist.
Pedal Feel
The hydro-boost generates a different pedal feel than a vacuum booster. Basic function can bechecked by pumping the brake pedal until hard with the engine off and then starting the engine whilemaintaining slight pedal pressure. Proper operation should result in the brake pedal sinking down andthen pushing back up against your foot. The sinking of the pedal when the engine was started is aresult of the power chamber being pressurized. Once the power steering system is at full pressure, itresults in the pedal pushing back against your foot pressure.
Diagnosis
The hydro-boost requires a constant source of pressurizedpower steering fluid for proper operation. Problems in thepower steering system will be reflected in the operation of the hydro-boost.Accurate diagnosis of a hydro-boost power assist devicedepends on combining an understanding of their functionwith a logical diagnostic approach. Hydro-boost problemsusually break down into the following categories:* Noise problems; * Slow or incomplete pedal return; * Over sensitive braking; and * Self applying brakes Note: Each of these is covered in the following sections.
Noisy Booster
1. Confirm complaint making sure to note type of noiseand when it occurs. If the noise occurs during high brakepedal efforts or quick pedal release, go to step 2. If thenoise occurs during low brake pedal effort, engine idle - nopedal effort, or normal driving conditions, go to step 3.2. Noise occurs during high brake pedal efforts or quick pedalrelease: See normal operation noises listed below. Mostlikely the noises being heard are normal based on the typeof conditions.3. Operate the vehicle until the engine is at normal operatingtemperature. Duplicate the operating conditions above andlisten for the noise.4. Compare results with the normal noises listed under themore info section and with a known acceptable system.
Normal Operation Noises
Properly operating hydro-boost units will produce certain noises. These noises occur, for the most partwhen the brake pedal is manipulated in a manner not associated with everyday driving habits. Thegeneral categories of normal operating noises are (1) hissing noises and (2) clunk/clatter noises.The hydro-boost will emit normal hissing noises when above-normal brake pedal efforts are applied(40 lbs. and up). The hiss sounds particularly noticeable with the vehicle motionless and will increasein intensity as pedal pressure increases above 40 lbs. and system operating temperature increases.Loud hissing sounds at or below normal (20 to 25 lbs.) pedal effort warrants investigation.Clunk, clatter or clicking noises will be heard when the brake pedal is quickly released from hard (50to 100 lbs.) pedal efforts.
Slow or incomplete pedal return:
1. Run pump at fast idle.2. Pull the brake pedal rearward with approximately 10 lbs. force and release. Measure thedistance to the floorboard.3. Make 100-lb. brake application. Release brake pedal and measure distance to floorboard. Thebrake pedal should return to its normal position (step 2). If measurements are the same, go tostep 5.4. If the brake pedal does not return properly, check the pedal to be sure it is operating freely.Correct any sticking or binding as necessary.
5. If brakes are self applying and pedal is free, check for obstruction in the return line or a kinkedconnection between hydo-boost and pump reservoir. If obstruction or kink is found, go to step6, otherwise go to step 7.6. Remove obstruction or replace line as required. If condition remains, check for a damagedreaction end. If damaged the hydo-boost should be replaced or repaired.7. If brake pedal is free of any binding conditions and return line is free of obstructions, removethe master cylinder cover.8. Observe the brake fluid in the reservoir while rapidly depressing the brake pedal one inch.9. Fluid surface should have some movement or spout in the forward reservoir section. Minor spouting may occur in the rearward reservoir. If no movement or spouting of fluid occurs inforward reservoir, the hydro-boost unit is defective and must be replaced or repaired.Excessive pedal effort - brake pedal chatter - pulsation and/or leaks:
Perform Basic Test:
1. Engine (pump) off, depress and release the brake pedal four times to deplete all hydraulicpressure from hydo-boost.2. Depress brake pedal and hold with light pressure then start the engine. If the power section isoperating properly the pedal will fall slightly and then hold. Less pressure will be needed tohold the pedal in this position. If the power section is NOT operating, go to step 3, otherwisego to step 4.3. If power section is not operating properly, check pump reservoir level. If level is low, add fluidand repeat basic test plus Hydraulic Leak Test (Steps 4 to 5). If fluid level is good, go to step6.4. Steering Hydraulic Leak Test: Thoroughly clean the hydo-boost unit and all hose connections.Start the engine and run at idle speed. If the hose fittings do not leak go to step 5.5. Check the hydro-boost for leaks. Apply the brake pedal with approximately 100 lbs. force andhold while checking hydro-boost hose fittings for leaks. Do not hold brake pedal at 100 lbs.effort for more than five seconds at a time. If the hydo-boost leaks, it is defective and shouldbe replaced or repaired. If no leaks are found in the hydro-boost or hoses, do not repair or replace them.6. Fluid level good: Check tension and condition of drive belt. If the drive belt is loose or damaged, tighten or replace as required and repeat the basic test (Steps 1-2). If pump speedis slow, adjust and repeat basic test. If pump speed is OK, perform pump flow and relief pressure test.7. If pump output is below minimum specification, replace and repeat basic test. If all test andchecks are OK, the booster is defective and should be replaced or repaired.8. If power section is operating, perform the following steps in order.9. Hydro-boost accumulator pressure retention test: Run pump to medium speed, apply brakepedal force to 100 lbs. for not more than five seconds and then stop engine.10. Wait 90 seconds and apply the brakes. Two or more applications should be power assisted. If applications are not power assisted the hydro-boost is defective and should be replaced or repaired. If applications are power assisted, go to next step.11. Thoroughly clean the hydo-boost unit and all hose connections. Start the engine and run atidle speed. If the hose fittings do not leak, go to step 5.12. Check the hydro-boost for leaks. Apply the brake pedal with approximately 100lbs force andhold while checking hydro-boost hose fittings for leaks. Do not hold brake pedal at 100 lbs.effort for more than five seconds at a time. If the hydo-boost leaks, it is defective and shouldbe replaced or repaired. If no leaks are found in the hydro-boost or hoses, do not repair or replace them. Perform the brake hydraulic leak test.13. Brake Hydraulic Leak Test - Depress and release brake pedal several times, then hold pedaldepressed with medium pressure of 25 to 35lbs. If pedal does not fall away, hydraulic systemis not leaking. If pedal falls away, go to next step.14. Pedal falls away under constant pressure - hydraulic brake system is leaking. Check for external leaks at wheel cylinders, calipers, hoses and lines. If no leaks are found, additionaldiagnostic steps are necessary.
Service
The hydro-boost in not serviceable in the field. If the unit is not functioning properly, it must bereplaced. The replacement process is straight forward, but bleeding can sometimes be tricky. I amoffering a choice of techniques in this area. Hydro-boost brake systems are supposed to be self-bleeding, but this does not always prove to be true.
Bleed Technique 1:
1. Replace any hydraulic line showing external damage. Install new seals for all disconnectedfittings (as required) and install an in-line power steering filter. Tighten all hose fittings to OEspecifications.2. Flush the entire power steering system using the vehicle manufacturer's recommended fluid.Fill pump reservoir to the proper level.3. Disable engine to allow cranking without starting. Block wheels, put transmission in neutral or park and set parking brake, then crank engine 5 to 10 seconds (avoid overheating starter motor).4. Refill pump reservoir as necessary. Repeat step 3 until level is correct.5. Enable the engine to allow starting. Start engine and let idle. Slowly turn steering wheel fromlock-to-lock a number of times.6. Turn engine off and inspect fluid level and condition. Add or remove fluid as necessary. If fluidis foaming, wait one hour then recheck level. Repeat step 5 and 6 until fluid level is correctand shows no sign of air problem.NOTE: Many of you are aware that Ford power steering systems are very prone to air-relatedproblems. The most effective way to remove air in these systems is to apply a vacuum to the power steering pump reservoir. This technique can be used on most power steering systems.
Bleed Technique 2:
1. Remove return line from hydro-boost and plug end with appropriate size plug or bolt.2. Connect two- to three-foot piece of clear hose to return port on hydro-boost unit. Place end of hose into empty container at least 1 gallon in capacity.3. Fill power steering pump reservoir with correct fluid.4. Disable engine to allow cranking without starting. Block wheels, put transmission in neutral or park and set parking brake, then crank engine 5 to 10 seconds (avoid overheating starter motor) while applying and releasing brake pedal slowly.5. Refill pump reservoir as necessary. Repeat step 4 until no air is seen in return line from hydro-boost.6. Remove clear hose from return port and reconnect return line from pump.7. Enable the engine to allow starting. Start engine and let idle. Slowly turn steering wheel fromlock to lock a number of times.8. Turn engine off and inspect fluid level and condition. Add or remove fluid as necessary. If fluidis foaming, wait one hour then recheck level. Repeat step 7 and 8 until fluid level is correctand shows no sign of air problem.
Procedure
Use either of these bleeding procedures whenever replacing or servicing any component in a hydro-boost system. Normal driving conditions will remove air that remains trapped within the system whencomponents are properly installed and there are no flow restrictions in the system. Always refer to thevehicle service manual for specific installation and testing procedures.
Power Steering Flush
In addition to requiring the correct pressure, it is also critical that the fluid be clean. The tolerances inthe moving parts inside the hydro-boost are such that only a small amount of contaminates can causea malfunction. This is especially true of the spool valve. The tolerances necessary to form a metal-to-metal seal are quite small and any contaminates or tarnish buildup can prevent smooth operation of the spool valve. Since the spool valve controls the flow of fluid into and out of the power chamber, it iscritical it functions properly.Any vehicle equipped with a hydro-boost power assist will benefit from a periodic power steering flush.
Thread Starter
|
Lead Driver
Joined: Mar 2008
Posts: 7,174
Likes: 377
From: Near Los Angeles
Really? Not one person in this forum has experience rebuilding a hydroboost? We're talking about a unit that has been around since the seventies!!
I also find nothing online regarding the rebuild. I guess I found a good topic for an article.
It's just kind of a pisser that nothing is around to read. I hate to go in blind, so to speak. I notice the kits are about $30--$50, and are mostly Orings.
I also find nothing online regarding the rebuild. I guess I found a good topic for an article.
It's just kind of a pisser that nothing is around to read. I hate to go in blind, so to speak. I notice the kits are about $30--$50, and are mostly Orings.
Laughing Gas
Joined: Dec 2007
Posts: 1,052
Likes: 2
From: Alvarado, TX
Just a thought, but you might want to post this in another forum, maybe a later model one. I also got an Astro unit at PYP and sucessfully installed it on my truck but I sure don't know anything about the innards. I bet most of the other guys in this forum are the same way. I would expect to find more technical info in a forum where hydroboosters are OE and more people have dealt with them.
Senior User
Joined: Jun 2006
Posts: 108
Likes: 1
From: Argentina, Southamerica
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Junior User
Joined: Feb 2010
Posts: 86
Likes: 1
I bought mine on rock auto. '99 F250 7.3L
Rebuilding the pump right now. Came on here to get some help disassembling it but no dice. The rebuild kit was under 10 bucks.
Rebuilding the pump right now. Came on here to get some help disassembling it but no dice. The rebuild kit was under 10 bucks.
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