brake failure warning light

Hi guys so my brakes have been acting up, when I first use the brakes the pedal feels really stiff like a malfunction with the brake booster, however that goes away if I keep driving. Now the pedal gets really soft like almost all the way to the floor and the brake failure light comes on and off. The softness mostly seems to happen at idle but can happen in regular driving. I did notice the brake fluid has dropped a little and I checked around the master cylinder and there are no leaks. I looked under the car to check the brake junction box and there was a very slight seepage around the sensor, but I'm not really sure because everything down there is pretty dirty. I was wondering if it seems likely that the master cylinder and the junction box are both bad, and that the stiff pedal is a seprate issue
thanks

Probably a good idea to include the year and model.

duh sorry I wrote this after work its a 1987 240 non abs wagon

The hard brake pedal is normal if there isn't any vacuum boost. You may have a leaky check valve or vacuum hose. I would agree with your diagnosis of the master cylinder being bad. I have had the warning light valve also cause a soft pedal. On the warning light valve the easy quick check is to take off the wire. Unscrew the switch and take it out of the valve. Any brake fluid on the switch or if you see brake fluid looking inside the hole means the valve is bad and should be replaced.

put an master cylinder on im trying to bleed the brakes but the front caliper bleed screws are stuck I already broke one..... anyways atleast the pedal isn't going all the way to the floor

Markos Simopoulos said:

put an master cylinder on im trying to bleed the brakes but the front caliper bleed screws are stuck I already broke one..... anyways atleast the pedal isn't going all the way to the floor

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Lots of penetrant, the correct size wrench and patience will prevent that. Sometimes it's unavoidable. Now you've got an excuse to replace your front calipers.

Or, bleed it at the brake line, where it threads into the caliper. Just crack open the brake line nut. I have bled brakes this way when the bleeder was broken off or stuck. Also, I would see if autozone rents a pressure bleeder. Looks like a big bug sprayer, screws onto the master cylinder where the filler cap goes. This allows you to pressure bleed them without using the brake pedal. This keeps the master cylinder cup seals from going into parts of the master cylinder that are rusty/crusty and tearing up the lips of the seals. Parts of the master cylinder where the cup seals don't normally go. oh, I just saw that you already replaced the master cylinder.

why didn't you bench bleed the master.... then you wouldn't have to bleed at the wheels

Even if you bench bleed the master cylinder. You always bleed an opened brake system. It just reduces how much you have to bleed at the wheels with a mater cylinder that is already done.

dl242gt said:

Even if you bench bleed the master cylinder. You always bleed an opened brake system. It just reduces how much you have to bleed at the wheels with a mater cylinder that is already done.

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this just isn't true.. at least for merican cars, but i just changed the master on the Saab and it's fine

I did "bench" bleed the master cylinder as best I could, but without a vice or return hoses so there was still some air was left in it. Anyways I replaced both front calipers and rotors let me tell you, was it a pain to bleed the system after that. The brakes do feel a little soft at the top but I think thats just because I didn't replace the pads but all 4 wheels lock up just fine so i'm happy. Anyone know why volvo does this thing with a million bleed screws though, besides you know to let air out?

It's a safety system. Look at a brake schematic for a non-ABS 240.