Hydro boost brakes sometimes get very tight

[EstatePlanStan]

I rebuilt my 1984 Chevy 6.2 liter diesel truck. In the process I replaced the hydro boost on the master cylinder. I went through the bleeding process of turning the steering wheel 5 times to one side then the other them depressing the brake pedal 3 times. I did this about 20 times. Now when I drive it the brakes work fine for a while but then without warning when I press the brake pedal it is very hard to push and there is little braking power. Then all of a sudden it depresses and the brakes are fine.

The hoses are connected correctly, the fluid is at the proper level. It acts like there is air so I did the same process again and no change. NONE of this happened before the rebuild process. What did I do wrong?

Stan

 

[Scottgenex]

I rebuilt my 1984 Chevy 6.2 liter diesel truck. In the process I replaced the hydro boost on the master cylinder. I went through the bleeding process of turning the steering wheel 5 times to one side then the other them depressing the brake pedal 3 times. I did this about 20 times. Now when I drive it the brakes work fine for a while but then without warning when I press the brake pedal it is very hard to push and there is little braking power. Then all of a sudden it depresses and the brakes are fine.

The hoses are connected correctly, the fluid is at the proper level. It acts like there is air so I did the same process again and no change. NONE of this happened before the rebuild process. What did I do wrong?

Stan

I have a long hydroboost thread that has some good info in it. Same problem. Except when mine acts up it gets worse. I don't get the good pedal back. No brakes. I have to let it sit for hours to get it back. Only thing I can think off top of my head for yours would be the dump valve in the unit. It can get contaminated easy. Maybe a good power steering flush would help yours. Make sure no leaks, etc.

Others with bigger brains than I can chime in and help. I never got mine to function. Replaced and rebuilt everything multiple times. Including going through 5 hydro units. Currently I'm going back to vacuum. Since your diesel, no choice but to solve it. I'm to the point that there's probably one or two companies that do the rebuilds and most units are faulty. I tried Rockauto, Napa, and Oriellys.

https://www.gmsquarebody.com/threads/hydroboost-hard-pedal.46460/page-3#post-1025995

 

[Snoots]

Did you use REAL p/s fluid or ATF? With hydroboost it's not 'one size fits all'. ATF tends to foam on a hydroboost system. Higher pressure and heat.

 

[YakkoWarner]

I am glad I stumbled into this topic! I have a friend with a P30 based motorhome that is having pretty much the same kind of hydroboost problem (and no way to revert to vacuum in the space available). He has had the system worked on multiple times with parts replaced, no leaks but the problem persists.

How hard is it to flush and replace the fluid? Is there a higher grade of power steering fluid recommended for hydroboost systems or will standard big box auto store stuff be safe to use?

 

[Scottgenex]

In the best way it's nice to know I'm not the only one struggling with new unit problems. Especially after a year of trying to figure it out.

Pretty simple to flush. Pull the low pressure return off the hydro, install a few feet of 3/8s hose (I think its that size) down to your choice of collection container, start up, steer one way and depress pedal, release, fluid will come out, repeat while filling the PS resovoir until it looks clean. Then perform the bleed procedure.

 

[fast 99]

On older vehicles would suspect PS pump performance is low, loose or worn belt, poor fluid condition. I have used mainly ATF without problems. I suppose the booster could have internal issues but not unit after unit. Common failures are leaks.

Bleeding shouldn't be a concern. Just start vehicle and press brake a few times and rotate steering side to side then a short road test. May be let sit for bubbles to subside in pump. Never had to do anything fancy.

 

[Blue Ox]

On older vehicles would suspect PS pump performance is low, loose or worn belt, poor fluid condition. I have used mainly ATF without problems. I suppose the booster could have internal issues but not unit after unit. Common failures are leaks.

Bleeding shouldn't be a concern. Just start vehicle and press brake a few times and rotate steering side to side then a short road test. May be let sit for bubbles to subside in pump. Never had to do anything fancy.

We cooked a lot of hydro boosts with ATF. Repeat seal failures until we switched to PS fluid.

Things may be different today, but when the truck was new ATF was a problem.

 

[stvaughn]

I am currently installing a hydroboost system on a 63 Impala. In researching the installation I came across some information that said to make sure that there was a small gap between the master cylinder push rod and the hydroboost piston otherwise the master cylinder will not retract completely and will not function properly. I checked mine when installing and found that the push rod was adjusted to long. I shortened it up to create a little gap. I have not put the system in service so can’t report on how it works. Not sure if this is your problem but might be worth checking.

Steve