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Discussion Starter · #1 ·
Ah, fun things that happen right before the long weekend!

This morning on the way to work I discovered my brakes were not working properly; instead of coming on gradually as I push the pedal the brake pedal has no resistance and does nothing until it's almost all the way in, at which point the brakes will slow the car but they don't feel particularly powerful. I traveled in to work slowly and I'm trying to find a mechanic that is free to have a look at it before the long weekend.

There is no error light or complaint from the car, other than "washer fluid low" which I've been meaning to fix for a few days. I had a quick look at the brake fluid reservoir, but I couldn't get the lid off or tell what the level was - the light wasn't good in the carpark and I was in a rush.

Is this likely to be a low/contaminated brake fluid issue, or something more involved (and expensive) like vaccuum system or master cylinder?
 

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The brakes are divided into two circuits, each has a front wheel and the diagonally opposite rear wheel. It sounds like one of the circuits is not working. The pedal collapses until the bad circuit's piston bottoms out, then the pressure goes to the good circuit.

There are a number of reasons that this could happen. You could have a leak somewhere in the system or a bad brake line. This would be seen by the fluid level being very low. There's a divider in the bottom of the reservoir so that the leaky side can not drain all the fluid from the good side.

You could have a bad master cylinder and one piston may not be sealing and can not generate pressure. This might leak inside the car by the pedals but probably not. This would usually not show a drop in fluid level.

John
 

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Discussion Starter · #3 ·
My mechanic can have a look at it tomorrow morning, so I'll just drive slowly and carefully over there after working back late to avoid the worst of the traffic.

If the brake fluid is low will I get any benefit from putting more in and not going through a full bleed process? If it will help I'll put some brake fluid in just to get to the mechanics safely.
 

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Discussion Starter · #4 ·
The brake fluid is low, but not low enough to trigger the low-fluid sensor. When I push the break I can hear a hiss noise from near my feet, as if air is being forced out a small hole.
 

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The brake fluid is low, but not low enough to trigger the low-fluid sensor. When I push the break I can hear a hiss noise from near my feet, as if air is being forced out a small hole. This tells me that we have a hole in the power brake vacuum chamber (the power booster).. But this condition would cause a hard pedal and the need for much more uumph to stop the car.
This can be tested using a vacuum pump with a gage, and adapter fittings.
Do maintain the fluid level at the brake fluid reservoir, when low, the pads should be inspected for wear.
 

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Discussion Starter · #6 ·
The proportioning valve was stuck open, and I'm not sure if the master cylinder has issues as well; I was more concerned with time frames when talking to the mechanic since they can't get parts until after the long weekend.
 
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