NEED HELP Brake Booster Valve Check

AzTruckGuy

Well-Known Member
Ok I made the mistake of thinking the Check Valve would be a easy replacement. It was, but now I have brakes that are basically hard to push down to get the vehicle to stop. Feel different than before, I have no vacuum in the system now. When I took off the old check valve, I heard the vacuum in the brake booster release as it made the sound. I replaced the check valve, turned the engine on and rev the engine to see if I get some pressure in the brake booster, drove it around and the brakes were hard to push down to stop. Went back and took off the new check valve and no vacuum sound, put on the old check valve and still hard brakes. So what I am doing wrong to get pressure into the brake booster?
 

therealsethallen

Well-Known Member
It's odd you mention that. I replaced my check valve today as well, and I had the dead opposite happen to me. It worked fine. I'm going to presume you did what I did the first time and install the grommet really poorly, creating a vacuum leak instead of fixing it.
 
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AzTruckGuy

AzTruckGuy

Well-Known Member
It's odd you mention that. I replaced my check valve today as well, and I had the dead opposite happen to me. It worked fine. I'm going to presume you did what I did the first time and install the grommet really poorly, creating a vacuum leak instead of fixing it.
I will check that but im pretty sure I installed the grommet tight againist the brake booster, the hose seems too long in my opinion
 
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AzTruckGuy

AzTruckGuy

Well-Known Member
Ok no dice, I am confused on how the check valve vacuums the brake booster, where is the vacuum that supports the brake booster since the check valve only allows vacuum in one direction and that's towards the engine?
 

therealsethallen

Well-Known Member
I'm not sure where to test it. What I can say though is that my grommet was cracked and it took me a bit to get the new one well seated. I'd check that.
 

AWD V8

Well-Known Member
To test a vacuum brake booster, with the engine off pump the brakes about 6 times. This will deplete the vacuum in the booster. Now, with your foot planted on the brake pedal, start the engine. If the booster is working, you will feel the pedal sink below your foot as the booster responds to the vacuum. If the pedal does not sink either the booster is bad, or you have no vacuum to the booster.

If the booster checks out OK, then you have a hydraulic problem or a friction problem if the brake pedal is hard to press to stop.
 
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AzTruckGuy

AzTruckGuy

Well-Known Member
To test a vacuum brake booster, with the engine off pump the brakes about 6 times. This will deplete the vacuum in the booster. Now, with your foot planted on the brake pedal, start the engine. If the booster is working, you will feel the pedal sink below your foot as the booster responds to the vacuum. If the pedal does not sink either the booster is bad, or you have no vacuum to the booster.

If the booster checks out OK, then you have a hydraulic problem or a friction problem if the brake pedal is hard to press to stop.
I have done the test with pumping the brakes and doesn't work. I don't feel the brake booster is bad as the brakes were working fine before I changed out the valve and it also had vacuum as it was released once the valve was removed.
3.jpg

The valve only vacuums in one direction and this direction is towards the engine, now when I removed the valve from brake booster, there was no vacuum in the hose from the brake booster connection, air was not being sucked into the valve, even with the hose still connected to the engine. I removed the hose that is connected to the engine, and the engine wanted to stall, which means air is being sucked into that port.

I am not able to get vacuum into the brake booster, since the direction of vacuum is towards the engine and the valve is not sucking air out of the brake booster, when the hose is connected to the engine port, but there is vacuum there. I blew through the hose and it was not blocked also.

WTF? I cant believe this lol
 
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AzTruckGuy

AzTruckGuy

Well-Known Member
I'm not sure where to test it. What I can say though is that my grommet was cracked and it took me a bit to get the new one well seated. I'd check that.
I removed the new check valve and put the old check valve back in and made sure everything was sealed and it is...I am having an issue with vacuum into the brake booster, which doesn't make sense at all
 

AWD V8

Well-Known Member
If you have vacuum to the check valve, which is pretty much for sure, connect the check valve to the hose, but leave it out of the booster. Start the engine. You should have suction on the check valve where it goes into the booster grommet. If no suction the check valve is bad.
 
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AzTruckGuy

AzTruckGuy

Well-Known Member
Valve Check was bad, which really surprised me since it was brand new, received an exchange. Trailblazer back to normal, pedal feels much better than before and the power seems to be back? Interesting that part has so much effect on the engine, but makes sense its going to inlet port by the manifold throttle area.
 

xavierny25

Well-Known Member
Don't know if I should start my on thread on this but I'm getting a hum sound when I'm on the brake. Let me clarify this a bit it's not as I'm braking or hard braking just when the car is at a stop an I have my foot on the pedal. No it doesnt hit the floor and the system is working correctly. Just an annoying hum while while sitting at a stop. The sound goes away once I let off the brake pedal and doesn't return till I'm back at a stand still. Any ideas what this could be? I'm planning on changing out the check valve but haven't diagnosis it as being bad.
 
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AzTruckGuy

AzTruckGuy

Well-Known Member
Don't know if I should start my on thread on this but I'm getting a hum sound when I'm on the brake. Let me clarify this a bit it's not as I'm braking or hard braking just when the car is at a stop an I have my foot on the pedal. No it doesnt hit the floor and the system is working correctly. Just an annoying hum while while sitting at a stop. The sound goes away once I let off the brake pedal and doesn't return till I'm back at a stand still. Any ideas what this could be? I'm planning on changing out the check valve but haven't diagnosis it as being bad.
I would recommend you remove your brake booster check valve and release the vacuum, put the check valve back in and pump the brakes 6 times to remove any vacuum and keep foot on brake and turn engine and let the system reset and vacuum itself and see if anything changes
 

therealsethallen

Well-Known Member
Just a thought. Another small rubber piece that pulls vacuum is this little ribber nipple on the intake manifold. I grabbed several of them from a-pull-a part. The one on my truck was severely ripped and caused a little issue memorial day weekend. Thank goodness for Duct Tape.

IMG_0752.jpg IMG_0751.jpg
 

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