AfterMarketNews Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Honda Civic: Failed PCMs And CAN System Diagnostics

It’s not unusual for me to get help requests through my e-mail. Sometimes it’s from working technicians, other times it’s from vehicle owners who can’t get their problems solved through professional repair shops. In early 2014, I received one...


Servicing Mercedes-Benz AIRMATIC Suspensions

The Mercedes-Benz AIRMATIC suspension system was introduced in 1999 on the S-Class and has subsequently been used on the E-Class and most of the automaker’s SUVs. The system employs electronically controlled air springs that provide an ideal balance...


Mazda: Performing Regular Undercar Maintenance

In this article, we’ll take a look at brake and undercar service on the Mazda vehicle lineup, with the footnote that even though this type of work ­becomes routine when you have a preventive maintenance mindset, good work habits from beginning to end...


The Ins And Outs Of Sanders

Sanders are required tools in today’s collision repair shop. Body techs and painters rely upon them every day to achieve that perfect finish on your customers’ vehicles. Whether you’re prepping a panel for paint or removing imperfections before...


Are You Regularly Maintaining Your Equipment?

Technicians who are idling because the welder won’t feed wire, the hydraulic ram won’t pull chains, the booth heater won’t heat or the air compressor won’t compress enough air is a costly mistake, as labor time is the most expensive thing in any...


Celebrate 'Back To The Future' Day By Watching The Time Machine Get A 2015 Detail

    For many today is just another Wednesday, but for a lot of people it is more than just your average Wednesday, it is "Back to the Future" Day. It is a day that everyone who watched the cult classic trilogy Back to the Future recognizes...


Solving Carbon Deposits In Direct Fuel Injection Engines

Symptom: Misfire codes, stumbling and suspicious fuel trim numbers. On a scan tool, the engine may show a loss in volumetric efficiency. The driver may complain about a loss of power, poor fuel economy and hard starts. Cause: Carbon deposits on...


Using Your Oscilloscope: Current Ramp Test Ignition Coils

Regardless of design configuration, the role of the ignition coil is to multiply battery voltage into high voltage. Following Ohm’s law for the conversion of volts to amperes, oil-filled coils generally require 3 to 5 amperes of primary current...


Serial Data Bus Diagnostics

Understanding The Function of Serial Data Buses If serial data buses did not exist, a wiring harness would have to be five times its normal size and use twice as many sensors to deliver the same level of functionality and safety we see in the modern...


Home Brakes Hydro-Boost Power Assist Systems: Operation Diagnosis and Repair

Print Print Email Email

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. There is no vacuum source available, as in diesel engines, or the vacuum source available is too 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 from a vacuum booster.

Hydro-boost has been used on a variety of vehicles since its 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 system works. A typical hydro-boost is shown in Figure 1. The hydro-boost is plumbed in line with the steering gear. 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 as a spool valve. Spool valves are used in a variety of hydraulic components, such as the valve body of an automatic transmission. A spool valve is basically a hollow cylinder with a number of rings machined into it (see Figure 2). The surface of the spool valve is highly polished 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 three ports. The path of the pressurized fluid from port 1 is determined by the position of the spool valve. The spool valve is positioned in figure 4 to allow fluid flow from port 1 to port 2 while port 3 is blocked by land #1. Figure 4 shows the spool valve moved to the left which changes 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, input rod assembly, a lever assembly, a power piston, spool valve assembly and an output rod. The housing is fitted with three ports as identified in Figure 6. The spool valve fits into a precisely machined bore that is part of the hydro-boost housing as shown in Figure 7. The fit between the spool valve and the bore is such that it creates a seal while at the same time allowing enough fluid between the lands and bore to provide lubrication. 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 the pressurized fluid from the power steering pump is allowed to flow to the steering gear, but not into the power chamber. The spool valve vents the power chamber to the return line of the power steering pump reservoir.

Pedal Applied
Once the brake is applied, the input rod moves forward (left) to the power piston assembly. The piston return spring is preventing the power piston and pin “A” from moving forward. This lack of movement causes the input rod to force the travel limiter valve assembly into the power piston which results in pin “B” moving forward. The lack of movement at pin “A” and forward movement of pin “B” causes the lever to pivot at pin “A”. The top of the lever moves forward (left) which results in moving 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 pump allowing pressurized fluid into the power chamber while at the same time maintaining the fluid flow to the 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 spring pushes the spool valve back to its rest position. This vents the pressure in the power chamber to the power steering pump reservoir through the return line. The power piston and lever assembly are returned to their rest position by return springs which in turn brings the brake pedal back to an unapplied position.

Similar to the vacuum booster, the hydro-boost is equipped with a backup or reserve in case the source of pressurized fluid is lost. A failure in the power steering system, such as a broken hose, broken power steering pump drive belt, or failed pump, would result in a loss of pressure to both the hydro-boost and steering gear. The hydro-boost uses a high-pressure accumulator to store power steering fluid under pressure in the event of a failure. There are two types of accumulators used, some hydro-boost units use an external accumulator, 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 assisted stops. Upon the first application of the brakes after an engine stall or loss of power steering, you would find approximately 60 to 75% of the normal assist available. If you were to release and apply the brakes again, you would find approximately 30% to 40% assist, then again approximately 10% to 20%, until you have depleted all stored reserve assist. Once you have depleted all of the stored pressure, the brakes will no longer have power assist and will be manual in their operations.

During normal operation, the accumulator is charged by pump pressure though a check valve assembly (See Figure 11). The check valve allows fluid into the accumulator, but prevents it from escaping. When the pressure in the power chamber is lost due to a failure, the input rod linkage will override the power piston linkage and cause the check valve to be opened. The open check valve will release the stored fluid in the accumulator into the power chamber which will provide the power assist.

Pedal Feel
The hydro-boost generates a different pedal feel than a vacuum booster. Basic function can be checked by pumping the brake pedal until hard with the engine off and then starting the engine while maintaining slight pedal pressure. Proper operation should result in the brake pedal sinking down and then pushing back up against your foot. The sinking of the pedal when the engine was started is a result of the power chamber being pressurized. Once the power steering system is at full pressure, it results in the pedal pushing back against your foot pressure.

The hydro-boost requires a constant source of pressurized power steering fluid for proper operation. Problems in the power steering system will be reflected in the operation of the hydro-boost.

Accurate diagnosis of a hydro-boost power assist device depends on combining an understanding of their function with a logical diagnostic approach. Hydro-boost problems usually 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 noise and when it occurs. If the noise occurs during high brake pedal efforts or quick pedal release, go to step 2. If the noise occurs during low brake pedal effort, engine idle – no pedal effort, or normal driving conditions, go to step 3.

2. Noise occurs during high brake pedal efforts or quick pedal release: See normal operation noises listed below. Most likely the noises being heard are normal based on the type of conditions.

3. Operate the vehicle until the engine is at normal operating temperature. Duplicate the operating conditions above and listen for the noise.

4. Compare results with the normal noises listed under the more 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 part when the brake pedal is manipulated in a manner not associated with everyday driving habits. The general 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 increase in 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 (50 to 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 the distance to the floorboard.

3. Make 100-lb. brake application. Release brake pedal and measure distance to floorboard. The brake pedal should return to its normal position (step 2). If measurements are the same, go to step 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 kinked connection between hydo-boost and pump reservoir. If obstruction or kink is found, go to step 6, otherwise go to step 7.

6. Remove obstruction or replace line as required. If condition remains, check for a damaged reaction 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, remove the 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 in forward 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 hydraulic pressure from hydo-boost.

2. Depress brake pedal and hold with light pressure then start the engine. If the power section is operating properly the pedal will fall slightly and then hold. Less pressure will be needed to hold the pedal in this position. If the power section is NOT operating, go to step 3, otherwise go to step 4.

3. If power section is not operating properly, check pump reservoir level. If level is low, add fluid and repeat basic test plus Hydraulic Leak Test (Steps 4 to 5). If fluid level is good, go to step 6.

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 and hold 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 should be 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 speed is 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 and checks 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 brake pedal 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 at idle 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 and hold 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 should be 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 pedal depressed with medium pressure of 25 to 35lbs. If pedal does not fall away, hydraulic system is not leaking. If pedal falls away, go to next step.

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, additional diagnostic steps are necessary.

The hydro-boost in not serviceable in the field. If the unit is not functioning properly, it must be replaced. The replacement process is straight forward, but bleeding can sometimes be tricky. I am offering 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 disconnected fittings (as required) and install an in-line power steering filter. Tighten all hose fittings to OE specifications.

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 from lock-to-lock a number of times.

6. Turn engine off and inspect fluid level and condition. Add or remove fluid as necessary. If fluid is foaming, wait one hour then recheck level. Repeat step 5 and 6 until fluid level is correct and shows no sign of air problem.

NOTE: Many of you are aware that Ford power steering systems are very prone to air-related problems. 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 from lock to lock a number of times.

8. Turn engine off and inspect fluid level and condition. Add or remove fluid as necessary. If fluid is foaming, wait one hour then recheck level. Repeat step 7 and 8 until fluid level is correct and shows no sign of air problem.

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 when components are properly installed and there are no flow restrictions in the system. Always refer to the vehicle 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 in the moving parts inside the hydro-boost are such that only a small amount of contaminates can cause a 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 is critical it functions properly.

Any vehicle equipped with a hydro-boost power assist will benefit from a periodic power steering flush. The only thing is you have to perform an additional step to ensure the hydro-boost power chamber and internal parts are flushed. When performing the flush, apply and release the brake pedal slowly to allow the new fluid into the hydro-boost. If you skip this step you will have the large quantity of old fluid in the hydro-boost that will mix with the new fluid once the brake is applied and released a couple of times.

Hydro-boost diagnosis and service is not difficult especially when you know how the system works. Applying this knowledge with a systematic approach will enable fast and accurate diagnosis of these systems.

The following two tabs change content below.

Bill Williams

Latest posts by Bill Williams (see all)

  • Daniel B

    I may have skipped over it, but I didn’t see the situation I have listed above. I really need to get my truck road worthy in a week or so!! My pedal goes straight to the floor, power steering works, but you can hear the pump whining. The truck is a 97 Super Duty bucket truck that I foolishly left sitting for a year through a VERY cold winter in Indiana. I’m kinda stuck and don’t want to throw random parts on with fingers crossed so ANY help would be greatly appreciated!

    • WeFixEmBest

      Daniel, I would say to walk through the diagnosis procedure listed above, to either identify or eliminate the hydroboost unit as the culprit. If the pedal “goes to the floor”, I would be more suspicious of the brake master cylinder, or air in the lines.

      • nancy

        I have a 2005 3500 Chevy duramax with allison transmission… has same problem as Daniel, the brake pedal going almost to floor and a whining noise. Now the whining noise is intermittent and now have a dry rubbing sound. I am not mechanically inclined, but the article has helped me understand the hydro-boost system somewhat. I have had my brakes checked several times and all service centers have said they are good. Now I am thinking maybe it is the brake master cylinder based on your response. Question: how or what would cause air to get in brake lines? Anyway I am off to a certified Chevy dealer to have the hydro boost system and master brake cylinder checked.

        • Buz Reynolds

          Each person on here need to purge the accumulator on there vehicle. Most are just a canister with a bleeder valve on them. Start the engine, put foot on brake, run it through its gears, then place in park.. letting it idle back the bleeder out, just like bleeding brakes. You may have to do it two or three time, but it’s most likely air in the system. It is the worst system any one ever came out with, and not easy to work on, as an individual. A shop maybe, but is your like me there is no close to where you live that work on them or even understand them. Lots of luck

  • mike

    i hv a 03 super duty,just changed steering gear box, flushed system replaced new atf fluid, brakes work fine, NO POWER STEERING

  • John C

    brakes on my 2001 Dodge Ram 3500 w/hydro-boost sink to floor board when I start the truck.

    • Chad Milem

      Same problem here John. I have a 99 ram 2500. Just changed the booster due to it leaking. Now, when i crank the truck, the pedal goes straight to the floor. Any suggestions?

      • Josh Shook

        Bad master cylinder, my 02 Cummings did the same thing my master was new or refurbish and it was bad out of the box so put my original back on and had my brakes back

  • TripleJackinGA

    I have an 84 P30 mini-bus. 6.2, automatic, power steering, & Hydroboost.
    It sat for several months. I put new batteries in this weekend, got it running great, now problems.
    1 or more brakes seem either dragging, or completely locked. Wide open, I could only manage maybe 20mph, & ciykd smell burning brakes.
    The pedal is very hard while running, & if I try to turn the wheel, I get a lot of squeal from the power steering pump. I did notice if I rev the engine, the steering gets slightly better.
    Any clue where I should start?

  • Roman

    i have a f550 2008 and i see break fluid mix to power steering fluid into the reservoir somebody now why this happen

    • Joe Johnson

      Where the master cylinder meets the hydro boost its leaking power steering oil. Could that be an O ring? Or does the hydro boost need to be replaced?

      • Carsten

        Joe, I have the same thing going on with my Dodge… what did you find out? Just a seal or does the whole n thing need replacement?

        • Jay Laursen

          I have similar problem on Chevy Express van 3500. Leak where master brake cylinder and hydro boost system connects. Seems the power steering fluid is leaking here. Do I need to replace the whole hydroboost system or just seal or o’ring?

          • Buz Reynolds

            Power steering fluid and Brake Fluid can not be mixed, if so it is important to get them fixed now. It is very dangerous. Find where there mixing at and fix the seal, then purge both system and flush with new fluid of each kind.

      • Josh Shook

        You can’t just buy seal , u have to buy the whole master cylinder it comes with the seal that’s where my 02 Cummins was leaking

  • werewithchrist

    Where can i buy a new or rebuilt hydro booster for my 83 southwind 454 c.i.d

    • jerry

      should be the same as a p-30 box truck that is what i ordered for my 85 southwind with a 454

    • Buz Reynolds

      The hydro boost for you 83 is probably just, what is called a control valve. I bought one for my 94 Bounder 6 mo. ago. You have to get everything from Workhorse, and they have escalated the prices out of this world, They had two left in the warehouse in WI, at the tune of $700. each. so I had to by one. There is a company has a fix fir this, but don’t remember who it is. it’s on irvforum.

    • Steve Rodrigues

      If I’m not mistaken u can purchase 1 at an auto parts store for around 200 or so…. Look at the pics for that years chassy

  • binder1466

    I have a 2007 2500 HD GMC when I apply the brakes and try to turn the steering wheel it is hard to steer I have replaced power steering pump and still having the same problem brakes works fine any sugestion

    • Buz Reynolds

      Accumulator has air in it.

      • BigCountry

        So how do you fix that?

  • fabiano santos

    quando aperto o pedal a direção endurece o que faço .;

  • ervin

    I have a 2001 ram 2500 5.9 cummins when I turn the steering wheel it makes the brakes apply to the point I can’t move the truck untell I let go of the wheel. .. any ideas

    • josh

      please let me know what corrected the problem iam in the same boat

  • Albert Catino

    I have a1979 GMC DURA VAN 3500 with a hydra boost brake system. After 10-20 min. Of driving the front brakes come on with out applying the brakes. This has even occurred while ascending a hill. Any HELP is appreciated. Thank you.

    • Jay Malinowski

      seen that one many times. either over full master cylinder or the push rod on the booster is too long. that will close the master cylinder fluid ports.

      • Albert Catino

        The push rod was to long, in mind also. Don’t know if it was the right way but I shimed the master cylinder out an the brakes work fine. I talked to a lot of so called mechanic’s an most said the booster was bad. Thank You for your reply and confirming my thoughts. Really appreciate it !

  • michael huston

    Got a 2011 chevy express 3500. Vibration felt in pedal and steering input. Input hose vibrates all the time, but worse when brake is applied and steering input. Fluid is full and changed to see if it would help. Old fluid looks a little metalic. Not sure if pump is faulty or hydra boost?

  • Rob

    I have a 93 winnebago vectra with 454 chassis. No doubt It has the hydro boost. After the engine warms up, there is a growling noise only when I step on the brakes, sounding like the power steering pump is low on fluid. Level is normal. The harder I push the pedal, the louder the growl. After releasing the pedal the noise goes away shortly. Any suggestions?

  • bob clements

    i have a 95 chevy g30 with hydroboost that leaks power steering fluid between it and the master cylinder even when the engine is not running. any help

  • Steve Rodrigues

    So the situation I’m having is a little different… Starts fine and drives fine but all of a sudden it locks up my front brakes and I’m pretty much stuck…. Has anyone else encountered the same situation?

    • Noal Owen Pitzoff

      Yes same thing happened to me. Is there and weeping/leaking of fluid from through your fire wall where the input shaft is connected to your break pedal? Mine is slightly leaking. I have a 2000 f250 7.3 power stroke

  • shane

    i have an 06 dodge 2500 5.9 with slow pedal return. if i remove the pump resevoir lid, it releases pressure and the pedal returns. Any ideas?

  • Josh Shook

    I have a Dodge Cummins and I installed my old rod in hydroboost because new one didn’t come with it started my truck and pedal went to floor why is that nothing is crossed because I have present lines

    • Tim Outland

      I just replaced the HB on my GMC K1500 on GM there are 2 different configurations 1 with short rod and one with a longer rod, I had to send one HB back as it required the shorter length rod, also I had master cyl go bad at same time that led me to thinking “new rebuilt” HB was bad, when I swapped master cyl I got my brakes back, if your master is bad make sure you get the correct master cyl, for hydroboost and not vacuum assist brakes .

      • Josh Shook

        My hydroboost didn’t come with a rod because it was a refurbished one from advance

  • carlos

    Hi I just replaced the power steering pump,gear box, bleeding the system and the fluid gets real hot to boiling point on a 83 suburban with a hydroboost,any suggestions it’s really appreciated, thanks

    • jason23

      Mine too , did you find the answer?? Maybe the Hydro booster? Please someone give a reply…

  • carlos

    Sorry a 93 suburban

  • David

    I have a 2003 Dodge and my front brakes some times will just start to have the death rattle when i put my brakes on in the mornings when it’s cold out side like my front rotors where warped but had them checked and they where ok help

  • Dan Thresher

    have a 2000 gmc savanah 2500 with a 350 engine. Bought van recently as spare work van. New rotors and pads as well as rear shoes…drums appear fine..after changing pads, brakes work great for 1 hour then go back to being over sensitive…1/4 inch pedal depress…face on dash….thinking master cylinder piston getting stuck….not sure hydro boost would cause this…any thoughts?

  • Kayla

    I have a 2005 2500 Dodge Ram. Ever since a lift was put on last January I would loose my brakes, the pedal would go to the floor and I would have to pump them and they would raise back up. We replaced the master cylinder. That wasn’t the problem, it has been months now and the problem will occur at random times.

  • Luis

    I have a 1999 Chevy 3500 and I have a problem when I Drive it and I turn the wheel the brake pedal press down itself.

    • josh

      did you ever figure it out iam having the same problem

  • tony vigor

    i have a 2003 Chevy W5500, my brakes not working, the fluid from the hydro booster is going in to the power steering pump, and the pedal of the brakes go down to the floor

  • Dale Thomas

    I have built a Factory Five Roadster. I’m using hydroboost. When car is at operating temperature, I have the following braking symptoms:
    At low speed stops, and especially when making right-hand turns during low-speed braking, I get loud noise coming from under the hood; not fan belt noise, more of a chattering/grinding noise. No pedal vibration during this noise. PS and brake lines bled good, many times, no leaks. Could it be related to incorrect positioning of the spool valve during pedal travel?

  • Michael Smith

    I have a 2008 Chevy 3500 hd with hydroboost, I had a problem with a front caliper locking up so I changed both front calipers and brake lines( rubber hoses). I changed my power steering pump a few months back. The problem I’m having now is my brakes slowly lock up through the course of the day and I have to bleed them to get them unlocked. Brakes work fine in the morning but the more I hit the pedal the harder they get, I find they lock up more rapidly of the truck idles for a lil while. When they are completely locked up the pedal is rock hard and has vibration in it. I’m just trying to figure out what to change next. Any help would be greatly appreciated

  • victor black

    I have a 1986 Chevy mini winnerbago r.v that have hydro problem is the brakes keeps locking up it would only stick when vehical sat for a while and tried to drive off I felt the brakes holding. Now when l try to take off the brakes automatically engages, slams on. What could cause this problem.

  • Travis

    I have a 1997 f450 superduty with a hyrdoboost system and changed my power steering pump now I have no power steering and brakes isn’t working good at all. I hooked everything up right I’m not sure what I should do

  • Brett

    I have a 98 Chevy 3500 4×4 and when i start the truck the brake peddle sucks to the floor with no pressure

    • Nicholes Allen Tavernier

      I am having the same problem

    • Nicholes Allen Tavernier

      I am flushing, bleeding, and trying all the advice giving on the forums. Ive contacted several shops and was told similar procedures ive already done. You tried tried the disabling ignition to run down compression throughboost ?? Running a clear hose to clear container from return line?

  • Rich Thompson

    I have a 1984 f600. The pedal is very stiff for about a second or so and then it has a normal feel. It feels like manual brakes for a second or so before it stops properly. What do you think is causing this? Thank you, Rich

  • Robert Booth

    I have a 1989 Ford F series Super Duty with new(remanufactured) power steering pump and gearbox. brakes work fine but pressure line blows off of power steering pump as soon as I start to turn the steering wheel. Could the hydro-boost unit cause this high pressure?

  • Roger

    I just changed the power steering pump and steering gearbox on my 02 Silverado 2500HD. After filling the pump with fluid and disconnecting the return line to pump reservoir, I removed the fuel pump relay from the electrical center in the engine compartment and cranked the engine to commence the bleeding process of the steering system. The fluid level in the pump didn’t move. It was as if the pump wasting doing anything. After cranking the engine many times and not getting any results, I reinstalled the fuel pump relay and started the engine. Nothing. The reservoir level didn’t move. I installed another pump and did it all over again. Same thing. I then removed the pressure line from the Hydro-Boost and literally sucked on it with my mouth to draw fluid in. I immediately felt an air bubble come through. I sucked on the line until the fluid filled the hose completely. (I know believe that filling the line completely wasn’t necessary. It was the air pocket in the control piston that needed to be removed.) I then re-attached the line at the hydro-booster and did a quick start and stop of the engine. SUCCESS! The reservoir immediately went down. After refilling it, I removed the fuel pump relay again and cranked it until fluid ran out of the end of the return line (still disconnected from pump reservoir) and then re-filled the reservoir and re-connected the return line to the pump. Up to this point I had not touched the steering wheel. I then cranked the engine while turning the steering wheel stop to stop and in both direction a couple of times. In hind-sight, I should have left the return line disconnected until this process was complete. But it didn’t seem to be an issue. I re-installed the fuel pump relay and removed the hydro-boost return line from steering pump reservoir and started the engine. I had a helper push the brake pedal down as far as it would go slowly release it. Upon releasing the pedal, oil flowed through the return line into a catch pan. I did this twice and re-attached the line to the reservoir. I reconnected the fuel pump relay and started the engine. I watched the fluid level in the reservoir closely and added fluid as necessary. Both the steering and the brakes work perfectly.

  • Roger

    Just to clarify my first post, the engine was was running when I bled the hydro-boost system.

  • Janina

    Just replaced my brake lines on my 2004 Chevy Tahoe with brake booster and now my power .steering quit working does anyone have any idea what’s going on ?

  • Jayson

    I have a 2002 Cadillac Escalade and I’m having problems wit my rear breaks no pressure I have only front breaks I changed almost every part to my breaking system someone told me it can be. My hydro booster??

  • Jayson

    Does any one have any ideas??i changed master cylinder abs pump break lines calipers …

  • john

    I have a Chevy 3500 hd , lost braking and steering. I pulled off the road and turned the truck off for about 15 minutes , checked and had all the fluids at right level. Restarted and everything seems normal. I guess I need to know if I should concentrate on the hydroboost or power steering pump.
    Thank you for any information

  • scott
  • Will Kerek

    I have a 1999 F 550 and when driving my pedal goes to the floor when you turn the wheel and I have already put a new booster on

  • Flash Pa

    I have a 2000 Wind Sport motor home. Hydro Boost is very hard to stop the 1999 Workjorse P31 chassis and pedal sticks near the floor and has to be pulled back up. Where do I start, as this is my first hydro boost system.

  • Donna Daytona

    Great ideas ! BTW , people want a a form , my colleagues found a blank form here

Latest articles from our other sites:

GF-6 Oil Specification: What It Means For Your Shop

The Obama Administration finalized fuel economy standards in 2012 designed to increase fuel efficiency standards to 54.5 mpg for passenger cars and light-truck applications by 2025. This push for greater...More

Hunter's Quick Check And Quick Tread Fully Integrated With AutoServe1

Hunter Engineering’s Quick Check and Quick Tread now fully integrate with the AutoServe1 digital vehicle inspection and customer communication system. According to AutoServe1, its product is one of...More

Registration Open for ETI’s 36th Tech Week

Since 1947, the Equipment and Tool Institute has been meeting with automakers in order to fulfill one of the association’s most important goals, which is to provide member companies an ongoing stream...More

STAR EnviroTech Sponsors U.S. Military Veteran Automotive Scholarship

STAR EnviroTech is working with the University of the Aftermarket Foundation (UAF) to fund a Military Veteran Automotive Scholarship. The scholarship is open to any active or honorably discharged...More

Continental Announces New VDO Xtreme LED Tachometer

Continental Commercial Vehicles & Aftermarket has announced the new VDO Xtreme LED Tachometer for street rod and hot rod enthusiasts. The company says it provides easy programmability, a top range...More


Shops should use a TPMS tool that can reset the sensor positions after rotation. There is a method in the owner’s manual to “match” the sensors that involves deflating a tire for eight seconds. On...More