# Need Brake Help



## tray (Jul 9, 2018)

Hello all, hopefully someone has an idea what is causing this problem.

I have a 2012 1.4 auto with 98,000 miles that is having a sporadic problem with the brakes. 
Symptoms:

Happens 1-2 times per week, no pattern or reason it happens
Only occurs when the car has sat
Only occurs at start up
No brake pressure when first starting the car
If I put the car in park and then restart moving it usually goes away. I have 1-2 times had to turn off the car and restart. After doing this the brakes function normally.
If I make a few errands the problem only occurs the first start after the car has sat for a minimum of several hours.

I am thinking this is a switch problem that after sitting gets stuck. Could this be the microswitch? I tried researching but could not find anything that seemed similar. 

Thanks for the help.


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## Robby (Mar 1, 2013)

Either the micro switch or the pump itself.......When working properly the pump will operate with each brake apply for 3/5 seconds.

You also are losing vacuum at the booster.....that plastic vacuum nipple plugged into the unit through a grommet has a one way valve in it.
I'm thinking yours is leaking and if it has been leaking a long time the vacuum pump may be on its last legs.

For now, focus on the vacuum loss and micro switch in that order.

Rob


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## tray (Jul 9, 2018)

Thanks. I will do some testing. If it is the grommet, would the repair be to just replace the hose with the microswitch.


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## tray (Jul 9, 2018)

I did the quick test with the car off of pushing on the brakes several times and then putting turning the ignition to see if the pump came on. The pump did not come on. Is there a way to test the pump and the microswitch to see which one failed? I checked the recalls on GM's website for my vin and it shows no recalls so I would assume the microswitch was replaced at some point.

Suggestions?


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## Robby (Mar 1, 2013)

Car must be running for the pump to run.....Best to have someone under the hood with their hand on the pump....you can feel them softly vibrate when running.....sometimes you can hear them.....again, head under hood.

As I said earlier, focus on vacuum loss. Forget electrical for the moment.

There are two vacuum sources for the booster Tee'd together. One is from the intake manifold. There is a one way valve at the hose to manifold junction. it allows vacuum from the booster to the manifold as long as manifold vacuum is less than the vacuum in the booster.
Because the engine is turbocharged, there are times the manifold will not have enough vacuum to charge, or maintain the charge in the brake booster......hence the necessity for the check valve.
The other vacuum source is the vacuum pump. The pump will charge (with vacuum) the booster through the other line at the 'T'. It is enabled by a micro switch that is actuated by a tiny diaphram in the line below that switch. Anytime vacuum is below a certain threshold in the line the switch is activated and as soon as vacuum is at a predetermined point the switch is deactivated.

All this stuff comes together at the booster unit and a plastic nipple that is part of the line is insered through a rubber sealing nipple on the booster. 
That plastic nipple is the visual part of a one way valve......it keeps the booster 'charged' with vacuum during periods of wide open throttle or when not running, so power assist is available at start up or if the engine stops running.
Generally the booster can provide two assisted stops before vacuum is exhausted.....from that point on, brakes are available with very high pedal pressure required.

Thats a whole lotta writing to tell you to start by performing a simple test.
After driving the car a few minutes and verifying the assist is working, shut it off. Raise the hood and with a rocking/pulling motion at the base of the check valve at the booster, pull it out of the grommet.
The moment it pulls out you will hear a loud hiss of vacuum.....remember the process and the sound and reinsert the valve. 
Close the hood, drive the car, making sure the brakes feel normal, park it for the night.

Following morning.......a good check valve and booster will not allow any apprecable vacuum loss......pull the valve back off BEFORE STARTING and if the valve and booster are in good order you will have the same hiss of vacuum loss.
If there is no vacuum held overnight you start by replacing the cheapest most likely to fail part.....the check valve, which in this case, I think comes with the micro anyways.
Same test, following day....no hiss, failing booster, loud hiss........sheeza feeeeex.

Rob


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## tray (Jul 9, 2018)

Robby, thanks for the help with this. 

Yesterday I did the vacuum test after driving the car around for a few minutes and did have the hiss when I removed the hose. This morning I did the same test after the car sat over night and also had the same hiss. 

Any ideas on what to test next?


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## Robby (Mar 1, 2013)

tray said:


> Robby, thanks for the help with this.
> 
> Yesterday I did the vacuum test after driving the car around for a few minutes and did have the hiss when I removed the hose. This morning I did the same test after the car sat over night and also had the same hiss.
> 
> Any ideas on what to test next?


Since the booster has proven itself I would be inclined to go for the micro switch and tube assembly......There have been secondary failures and a switch has moving parts, and it is fairly inexpensive.
Since the booster has vacuum and holds vacuum overnight the odds are the pump has not been forced to run constantly and shorten its lifespan.

Rob


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## tray (Jul 9, 2018)

is there anyway to test the switch with a multimeter? I agree with the switch has probably failed. When I started the car and backed it out of the driveway the brakes were very week with no assist so more than likely the switch is erratic and not turning on the pump.


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## Robby (Mar 1, 2013)

tray said:


> is there anyway to test the switch with a multimeter? I agree with the switch has probably failed. When I started the car and backed it out of the driveway the brakes were very week with no assist so more than likely the switch is erratic and not turning on the pump.


I'm sure you could but I don't know the values......I guess you could use a ohmmeter but because it is intermittent, the testing is pointless.
If your luck is like most it'll test ok......but is it?

Rob


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## tray (Jul 9, 2018)

I was able to fix the brake problem this morning. It ended up being the switch. As a note, I found that if you pull the vacuum line and leave it unattached and then turn the key so the accessories activate the pump should come on and you should be able to hear it. Before installing the new switch I tried this and nothing happened. After turning on the accessories the pump with the new switch the pump ran for about 5 seconds and the booster had full vacuum. 

Since the switch is only two wires my hunch is you could just jump them to determine if the switch or pump are bad. I did not try this but someone with a little more electrical knowledge could weigh in.


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