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hydroboost problems

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hydroboost problems

83chevyC-10350 83chevyC-10350
New User | Posts: 11 | Joined: 07/11
Posted: 10/14/11
11:33 AM

i have an 89 chevy R3500 with a 350, my issue is when i turn the steering wheel it also pulls the brakes while its running, which in turn locks up the front brakes, need some help, not real familiar with the hydroboost systems, i cant figure out whats wrong with it, help me out  

chevelle83 chevelle83
Addict | Posts: 2280 | Joined: 11/09
Posted: 10/14/11
08:01 PM

was the system working fine then this issue started all of the sudden?

 I am getting this from your post "while turning the wheel it is applying the brakes"

 is that the problem you are trying to tell?  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 10/14/11
08:12 PM

i would start with this offsite article.. written for professional mechanics...

it has some of the trouble shooting...

pay close attention to pulling the pedal up.. releasing it.. measuring the distance to the floor..


pushing the brake pedal with 100 pounds of force..

releasing the pedal..  and measuring the height off the floor again...   it should be the same..

if the pedal is binding.. you will have self applying brakes..

there is a chance that you have seized brake calipers and or damaged hoses..

read the article ..

post your results..  i will look around for more info..  

83chevyC-10350 83chevyC-10350
New User | Posts: 11 | Joined: 07/11
Posted: 10/15/11
08:04 AM

yes this did happen all of a sudden from out of nowhere, was turning onto my street moving about 15-20 mph and then just stopped on a dime, i have noticed that some of the lines have some fluid on them right underneath the reservoir but i dont think that any of them are damaged or leaking, the brakes were fine when moving in a straight line, but as soon as i would make a turn, the brakes would apply themselves, i suppose i can check out the calipers and stuff up front and see if those could be part of the problem, ill post my results, thanks for the info, youve given so far i really appreciate it  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 10/15/11
12:34 PM

more info.. from another forum...

Though not as common as vacuum booster power brake systems, the Bendix "Hydro-Boost" system dates back to 1973. The system uses hydraulic pressure generated by the power steering pump rather than engine vacuum to provide power assist.

Inside the Hydro-Boost unit, which fits between the master cylinder and brake pedal the same as a vacuum booster, is a spool valve and piston assembly. When the driver steps on the brake pedal, the pushrod slides forward and changes the position of the spool valve. This opens a valve port that routes power steering fluid into the cavity behind the piston to push it forward and apply the brakes.

Another component in the system is a pressure "accumulator." Some are nitrogen pressurized while others are spring loaded depending on the application. The accumulator's job is to store pressure as an emergency backup in case pressure is lost (engine stalls or power steering pump drive belt breaks). There's usually enough reserve pressure in the accumulator for 1 to 3 power assisted stops.

Problems with this system can be caused by spool valve or piston wear inside the Hydro-Boost unit, fluid leaks or loss of pressure (worn pump, slipping pump belt, etc.).

A simple way to test the Hydro-Boost system is to pump the brakes five or six times with the engine off to discharge the accumulator. Then press down hard on the pedal (about 40 lbs. of force) and start the engine. Like a vacuum booster, you should feel the pedal fall slightly when the engine starts, then rise.

The leakdown of the accumulator can be checked by pumping the brakes several times while the engine is running, then shutting it off. Let the car sit for about an hour, then try the brakes without starting the engine. You should get 2 or 3 soft brake applications before it takes more effort to push the pedal.

Slow brake pedal return may be caused by excessive seal friction in the booster, faulty spool action or a restriction in the return line to the pump.

Grabby brakes are probably the result of contamination in the system or a broken spool return spring. If the brakes tend to go on by themselves, you've probably got as case of restricted return flow or a defunct dump valve.

Excessive pedal effort can usually be attributed to internal leakage or the seeping of fluid past the accumulator/booster seal.

If a problem turns out to be in the booster itself, you'll have to replace it. Be sure to depressurize the accumulator by pumping the brake pedal half a dozen times before you open up any plumbing connections, other wise you might get blasted by high pressure brake fluid.

and more info on flushing the system..

you will probably want to do this flush before changing the hydroboost.. so you don't introduce old fluid into the new hydroboost..

the more i think about this.. the more i would start with a flush first..

may OIL CHANGE services have a power steering fluid flush machine.. actually an exchange machine...

it has 2 big tanks..  one with fresh fluid.. one for old fluid.. a twin tube dispenser tube.. it will remove and install fresh fluid at the same time.. while the engine is running and one of the techs is working the steering wheel back and forth and depressing the brake pedal  many times...

Under the hood on the driver's side next to the fire wall up high there is a rubber return line w/ a spring clip holding it on. It's real obvious and the only one there. I removed the clip and hose, then attached a piece of clear 3/8" tubing 6.5ft long onto the fitting using a small hose clamp. Ran the other end to a catch pan on the floor. Start the truck, in park, slowly depress the brake pedal as far as you can and hold it. Then turn your steering wheel clockwise 1/4 turn, back to center, then 1/4 turn counter clockwise then back to center. Slowly release the brake and re-apply and turn steering wheel again. Continue this until you hear the pump make noise (mine took 3 iterations). Stop immediately and turn off truck. Fill the power steering reservoir with fresh power steering fluid

Then repeat this procedure until you see clear fluid coming from the hose. Make sure that you put something on the hose in the catch pan to hold the end of the hose in the pan. Mine took a little over 3/4 of a gallon. Probably more than I needed but I wanted to get as much old stuff out as I could, and like I said, the old fluid was BLACK! Then, remove the clear hose and reattach the rubber return line. Also, make sure there is enough new fluid left over to refill the power steering pump when you're done. AND, after you refill for the final time, start the truck and move the wheel back and forth, then recheck fluid level, add if needed. All done.

1980_C-10 1980_C-10
New User | Posts: 2 | Joined: 09/12
Posted: 09/22/12
05:15 PM

im having a problem with my hydroboost system as well.....i have an 80 model c-10 silverado and ive replaced the master cylinder, both front calipers and both wheel cylinders but i was still having a return problem.....then i turned my attention to a type of valve.....and now the name escapes me....but it had 4 ports for brake lines and it sat on the frame between the front was appearntly a dealer part only so i called chevy they said it was discontinued....please forgive my ignorance im 26 and just getting into older vehicles.....can sombody tell me what this valve is called and where to find going to continue looking for hydroboost schematics and try to find this thing....thanks guys  

Dave632 Dave632
Addict | Posts: 2218 | Joined: 07/08
Posted: 09/26/12
06:00 PM

I had Hydroboost on a couple of trucks and I hated it. Nothing but trouble.  

chevelle83 chevelle83
Addict | Posts: 2280 | Joined: 11/09
Posted: 09/26/12
07:49 PM

proportioning valve,  is what your looking for. It balances the brakes from front to rear to prevent the rear wheels from locking up.  

pepsi1 pepsi1
Guru | Posts: 1718 | Joined: 09/11
Posted: 09/27/12
02:43 AM

Yeah Dave but when they worked they worked....

If the brake light isn't on in the dash, then you don't have a hydraulic failure.

Look don't start throwing parts at it, because those systems are very expensive.There are check valves and other components that go bad in those systems also...
1.The power steering pump plays a big part in that system also.

2.The front brake line hoses may have collapsed internally, and is keeping pressure in the caliper, and as soon as you turn the steering wheel the system gets more pressure and bang it puts the brakes on. (You would get that to happen all of a sudden)

3.Get the complete front end off the ground if possible. or one side at a time.Have a helper start the engine, and just step on the brakes. If the tire doesn't turn right away look for a problem in the lines or a caliper.

4. If they release rather quickly then start with the booster. They are expensive believe me...Good Luck...Keep us posted...

I would go that route first. I had a guy tell me he had a problem with his front brakes,takes me for a ride at about 50 and the R/Front brake locked up and almost turned us around. It was the brake line that collapsed internally, didn't tell you he had a 32' camper attached to the truck...I wanted to punch this Aquaduct...LOL...Scared me. Confused