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Brake pedal sticking/brakes staying on


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So my brake pedal keeps sticking down a little bit, engaging the brakes.

Not locking them up, just dragging.

And my brake lift stays on too since the pedal doesn't come back up all the way.

 

Got a new booster, 2nd new one actually because on the first one, the rod was too long and the brakes kept locking up and staying on and wouldn't release.

So got a 2nd booster...

It had a junk yard Grand Cherokee master cylinder on it. We replaced it before changed the booster.

So it's got a 2nd, brand new MC on it...

 

Is there a maximum amount of vacuum to be run to these boosters?

 

My alternator creates vacuum for brakes and we're not sure of maybe it's killing all the boosters we put on.

These two problems (locking up 1st time and sticking a bit now) didn't happen as soon as new parts were installed. It's taken a couple months for the problems to start back up again...

 

Any ideas?

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My alternator creates vacuum for brakes and we're not sure of maybe it's killing all the boosters we put on.

 

 

How does that work?  All my vehicles get their vacuum from the intake manifold.  I've never seen a system where the alternator supplies the vacuum.

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Stick a vacuum gauge on it and see how much it's pulling and if vacuum is steady at the booster. Check for leaking / collapsing booster vacuum hose, and if the check valve is working.

New check valve, all lines are good.

We took everything apart and put it back together, the same, nothing caught our eye as wrong or malfunctioning, and now it seems to work fine. Well for 1 day so far.

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  • 3 weeks later...

Try these brake booster checks:

 

Test Power Brake Booster

If the pedal feels "hard" while the engine is running, the booster isn't operating correctly. If you suspect the booster is defective, do not attempt to disassemble or repair the power booster. Doing so is unsafe and will void your warranty.

Test 1

  1. With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
  2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the booster is working properly.

Test 2

  1. Run the engine a couple of minutes.
  2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.

Test 3

  1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight.

Inspect the Check Valve

  1. Disconnect the vacuum hose where it connects to the intake manifold. Do not disconnect the vacuum line from the booster. Air should not flow when pressure is applied, but should flow when suction is applied. If air flows in both directions or there is no air flow, the valve needs to be replaced.

Verify Enough Vacuum

  1. Check the operating vacuum pressure when the engine is at normal operating temperature. There should be a minimum of 18 in. of vacuum. Vacuum may be increased by properly tuning the engine, checking for vacuum leaks and blockages in vacuum lines.
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  • 2 weeks later...

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