ymanchik

Random loss of brake pedal pressure, occasionally

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Happened today. Start up the car, go driving, brakes work great. Next time I start it up and drive, there is no brake pressure, I have to press the pedal 3-4 times to get it to brake. Shut it off, start up again and brakes work fine. Any idea what the problem could be and what I should check first? This has happened before, it just comes and goes randomly. Hasn't been a big deal so I've been putting it off. But I've got some time and need to get this fixed.

 

Thanks guys!

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First thought, master cylinder.

 

t

 

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17 hours ago, ymanchik said:

Next time I start it up and drive, there is no brake pressure, I have to press the pedal 3-4 times to get it to brake. 

 

When you say "no brake pressure", are you saying the pedal goes to the floor?  If you're losing pressure and it goes to the floor and then doesn't do it the next time I'd start with the master cylinder.  If it gets hard and then works normal it could be booster/vacuum related.

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1 hour ago, dang said:

 

When you say "no brake pressure", are you saying the pedal goes to the floor?  If you're losing pressure and it goes to the floor and then doesn't do it the next time I'd start with the master cylinder.  If it gets hard and then works normal it could be booster/vacuum related.

Yes, it goes all the way to the floor. But if I press it 3 times real quick then it gets hard. And that only happens some of the time, most of the time it works like it should. Would bleeding it be the easiest/fastest thing to check first before I look into the booster?

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3 hours ago, ymanchik said:

But if I press it 3 times real quick then it gets hard.

At the risk of being labeled a wise guy...how about some Brake Viagra?

 

More likely, a bad cup/seal in the M/C can allow fluid to pass by it, causing the low/no pedal without an external leak.  More likely with an old single M/C, but possible with a dual one.

 

And if that isn't the problem, you might check to see if one or more of your front caliper pistons is sticking in the extended position.   That can allow extra volume in the hydraulic system, allowing excessive pedal travel.  

 

Post whatcha find--this is an interesting problem..

 

cheers

mike

Edited by mike

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First thought, master cylinder.

Jus' sayin'....

 

t

 

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How old are the rubber brake hoses? If you are not loosing fluid I don't think it is the master. It you lines are shot,i.e will stretch or expand, you would get exactly what you are describing. Caliper stuck out would cause a drag and you should be able to feel that so I would rule that out. How long in between drive when this happens?  Pull a wheel at a time and pump up your system having someone look at the rubber lines.... you are sure you are not losing fluid?

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8 minutes ago, JayMac said:

How old are the rubber brake hoses? If you are not loosing fluid I don't think it is the master. It you lines are shot,i.e will stretch or expand, you would get exactly what you are describing. Caliper stuck out would cause a drag and you should be able to feel that so I would rule that out. How long in between drive when this happens?  Pull a wheel at a time and pump up your system having someone look at the rubber lines.... you are sure you are not losing fluid?

I'm guessing they're the original old ones, I'll double check when I get it on the jackstands. From what I can see I'm not losing any fluid. I would say maybe every 3-5 drives it loses pressure for a bit.

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Well if you are not losing fluid the system is "expanding" somewhere when you attempt to pressurize it. Not saying this is it but it is where I would look.....along with every other place mentioned.

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 I don't think it is the master

 

 

...but it is.  Really.

 

[/thread]

 

 

t

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Always willing to learn. If the fluid is fine what is going on?

master-cylinder-diagram.jpg

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