How to tell If hydro boost is working?

[Big T]

The brakes on my '99 Burb are weak. Feels like there's no power to the braking system. Above 50 mph I can stomp on the brakes and it takes awhile before they really start to grab. ABS light is on, but it's been that way for years. It takes quite a bit before the wheels will lock up.

I know the hydro boost runs off the power steering pump, but that is the extent of my knowledge on the system.

I just would like to have better braking power than what I'm seekng.

 

[THEFERMANATOR]

Try unplugging the solenoid in the power steering line coming out of the pump(if you have one).

 

[Big T]

What am I looking at? Hydro boost is at the firewall? Then the master cylinder? I don't see any wires going in there.

 

[6.2 turbo]

No,on the power steering pump. I didn't know hydroboost vehicles had this ?

 

[WarWagon]

What kind of pads you running? Brand/type? I find Autosuck pads are the worst and Wagner Quiet Stop bring it on and shut it down fast. The rear shoes also make a difference as the expensive over $100 parts also help. Are the rear shoes adjusted? Every other oil change I make sure they are snugged up.

At idle pump the brakes a few times. Shut engine off. Pump brakes 4-5 times - this drains the accumulator. Now the 6th brake press should be stiffer pedal than with the engine running. If it's the same force as with the engine running the hydroboost system isn't working. I don't know how the variable assist on later years works.

 

[THEFERMANATOR]

No,on the power steering pump. I didn't know hydroboost vehicles had this ?

Some 6.5 BURBS got it. I wouldn't have believed it, but a few members years back posted pics of there 6.5 BURBS with hydroboost having the solenoid at the power steering pump to cut the steering output at speed. If it sticks on, you could also lose some of your brake assist.

 

[Big T]

What kind of pads you running? Brand/type? I find Autosuck pads are the worst and Wagner Quiet Stop bring it on and shut it down fast. The rear shoes also make a difference as the expensive over $100 parts also help. Are the rear shoes adjusted? Every other oil change I make sure they are snugged up.

At idle pump the brakes a few times. Shut engine off. Pump brakes 4-5 times - this drains the accumulator. Now the 6th brake press should be stiffer pedal than with the engine running. If it's the same force as with the engine running the hydroboost system isn't working. I don't know how the variable assist on later years works.

Been through all this. Raybestos Advanced Technology pad and whatever was recommended for shoes in prior threads. Braided stainless lines. Upgraded splitter or proportioning valve. Larger cylinders from 1 ton dually on the rears. Done it all and the brakes are like a white knuckle hope and change ride at highway speeds.

I will try the brake pedal test tomorrow and report back.

 

[schiker]

Another similar test is with truck off press the brake pedal 3-5 times like you are bleeding brakes to drain the accumulator. The pedal will sink down and not want to rebound fully. Hold the pedal down and crank the truck up. The power assist should push the pedal back up against your foot maybe half way to top or more. You should definitely feel it push back up from when the truck was off.

Look for any leakage under the dash and on the firewall. There is a weep hole under the hydro boost.

How about your brake master cylinder ever replaced?

On bleeding the system have you tried a Motive Products bleeder. They look like a pump up garden sprayer tank with a hose that runs to an adapter on master cylinder. IMO they are the best bleeders and makes it pretty easy for one person to flush and bleed the system.

 

[btfarm]

How new is the pump. ThatA workrn out pump will act the same.

 

[Big T]

Alright, I did the "Schiker test" and the pedal sunk a bit further after starting it. Never rose against my foot.

No leaks. Never replaced master cylinder though I noted the PO had a new replacement in the box of parts that came with it (still have). Have never replace power steering pump as my steering works fine. Have replaced the fluid.

So where do I go from here?

I still have the '95 wreck in the backyard and the those brakes were working.

 

[schiker]

Try it again with this in mind.

Ok, I just checked mine again and if I hold it to the floor hard after bleeding accumulator it didn't push back all that hard. It sank just a bit then pushed back a little and was more firm. When I take my foot off the brake and reapply the pedal is much higher and firmer at the top.

My driveway has a slight grade to it and when truck is off I have to press the brake firmly to stop rolling after the 4-5 pumps to drain the accumulator. Once the truck starts up and I let off brakes it'll roll and when I reapply brakes it will jerk to stop with very light brake pedal and the pedal is near the top fully rebounded.

Since I am a 5 speed you'll have to try it with truck in neutral on a slight grade to mimic.

 

[Big T]

Alright went back out and tried it again per your descriotion. 'It ticks down ever so slightly with corresponding slight tick up after starting. Let the pedal up and step on it again and it had this weird rachet down motion to the floor with audible ticks all the way down. Happened several times. Pulled truck out for a spin and the brakes were very grabby in both forward and reverse, but that was in the driveway. Drove it down the street and it easily locked up the wheels at 40 mph. It slides slightly to the driver's side with all four wheels locked. The real test is from highway speed.

Doing this at 6,750' elevation. Absolutely no wind. Pretty funny how long my diesel smoke is lingering in the hood.

 

[Big T]

OK went out and did it a third time. On starting, the pedal sank slightly and no force back. Let the pedal up and re-apply and it goes all the way down and at the end I got this short buzz sound that was fairly loud and lasted a second or so. Re-applied the brakes a couple more times and it simply went to the floor and no further buzz sound.

 

[schiker]

If your hydro boost wasn't working I think you would know it and it would take a fair bit of pedal pressure to stop. If your pump is weak I think you feel it especially turning and braking simultaneously at idle. Every once in a while I feel my power assist get a little weak for a brief second or so when I am in a parking lot braking and turning hard while at idle or just under lugging just a bit. So some weakness is kind of normal or it will lug the engine a bit more. You feel it. And you can feel it when it goes back to normal when you stop doing both at the same time.

My brakes in general work ok like normal. My ABS light is on too. A panic stop at city speed will lock rears at least momentarily. But I wouldn't say it'll stop on a dime.

Have you ever flushed your power steering fluid?

 

[schiker]

OK went out and did it a third time. On starting, the pedal sank slightly and no force back. Let the pedal up and re-apply and it goes all the way down and at the end I got this short buzz sound that was fairly loud and lasted a second or so. Re-applied the brakes a couple more times and it simply went to the floor and no further buzz sound.

I was writing my post when you wrote this. That does not sound correct. Once my truck is running it is night and day different pedal rebound and feel. It is always at the top with light pedal pressure to feel the brakes working when the engine is on. Unless if I panic stop or have to brake hard then it sinks the pedal pretty far.

 

[Big T]

If your hydro boost wasn't working I think you would know it and it would take a fair bit of pedal pressure to stop. If your pump is weak I think you feel it especially turning and braking simultaneously at idle. Every once in a while I feel my power assist get a little weak for a brief second or so when I am in a parking lot braking and turning hard while at idle or just under lugging just a bit. So some weakness is kind of normal or it will lug the engine a bit more. You feel it. And you can feel it when it goes back to normal when you stop doing both at the same time.

My brakes in general work ok like normal. My ABS light is on too. A panic stop at city speed will lock rears at least momentarily. But I wouldn't say it'll stop on a dime.

Have you ever flushed your power steering fluid?

i believe that I flushed it when I did the steering box top off.

 

[Big T]

I'm thinking master cylinder now, given that the pedal does not firm up when I re-apply.

 

[Will L.]

No solenoid that Ferm mentioned?

You already have one, so I would swap master cylinder out. I know you've already replaced brake fluid from other attempts, but a quart of new fluid is so cheap it is worth it. Don't use an old bottle opened up before, your humidity is high enough to wreck brake fluid in short order.

You have the other master cylinder the PO had, if you use it: put it in the vice and pull it apart first inspecting the orings and seal. They could have dried out and not give you a real result. Also you can examine the bore and ensure no surface rust occurred in there while on the garage shelf.

I realize this way is more of a pain in the tail feathers, however while chasing this problem you need to take extra steps along the way to ensure no added issues. At least this is mostly labor except $20 at Walmart for some fluid.

Beyond that you're into more diagnostics:

http://www.jegs.com/i/Strange+Engin...9&cadevice=m&gclid=CK37jefnqsQCFRSVfgodW14AdA

 

[Big T]

I don't know where to look for the solenoid. There's nothing with wires going to it on the hydroboost a.

 

[Will L.]

On the back of the pump. If you do not have it, all you will see is the metal tube soldered to the back of the pump the return hose attaches to with a hose clamp, and a female fitting in the pump that a pressure hose screws into. If there is anything else back there you can be looking at a mechanical evo that can fail, or if it has wiring going to it on the pump- that is the solenoid. Electric solenoid can be unplugged, and a mechanical evo requires a bypass kit.

If you have just the basic pump, all you can do to verify it is not the problem is do a flow and pressure test. Definitely test it before you replace it, a bunch fail out of the box.