80L48

My Brake warning light came on the other day, and my brakes seemed soft/squishy. when I looked at all of the brake calipers, I noticed my passenger front caliper was leaking a very small amount of fluid leaking. I replaced the caliper and bled all of the brakes, but my brake light still comes on and the brakes are still squishy. When bleeding them, I can get all the air out and the brakes feel nice and firm. However, when I crank the car, the brakes become soft and squishy again and the light comes back on intermittently. Turn the car off, and they are firm. I do not see any drips/leaks anywhere (Master cylinder, Lines, Calipers). I replaced the master cylinder less than a year ago. I am wondering if the master cylinder is failing or the brake booster is??? I do not see any fluid drop, but I am not driving the car.

I also notice that the car rpm's go up slightly when I press the brakes, Is this normal with a brake booster powered by manifold vacuum?

DUB

RPM's going up when you press the brake is a sign of a bad booster.

I have also had the brake warning switch in the proportioning valve sometimes act up and make take a little while for it to correct itself.

ALSO make sure your hand brake is all the way down...because the brake warning light comes on when you pull your hand brake also.

If you disconnect the vacuum hose going to your vacuum booster and plug it. AND crank the engine and press on the brakes and your idle DOES NOT go up...then logic would dictate that you do have a bad booster.

DUB

Big2Bird

Sometimes a few good hard jambs on the brake pedal centers the switch.

'75

It can also jar loose a stubborn air bubble that's causing a soft pedal!

80L48

Thanks or the replies.

Yes, Emergency brake is all the way down and that switch activates properly when I raise it.

I'll try the vacuum disconnect tomorrow and reply. would the Brake warning light come on with a bad brake booster?

As far as the proportioning switch, I have been pressing the pedal LOTS of times to try to get this sorted.

I had the impression the Brake warning light was only for the Emergence Brake and Proportioning valve...

Big2Bird

Correct.

'75

You are correct, the brake warning light is only for the parking brake and the failure switch on the proportioning valve.

A bad/leaking booster will not give a soft pedal. I have see them give a momentary rpm change when the brake pedal is pressed due to some of the vacuum is being used. You can test it by running the engine, then turn it off and then pull the vacuum check valve and hose off the booster, you should hear it suck in air. If it doesn't hold vacuum, it could also be a bad check valve, but this won't affect the warning light or give a soft pedal.

80L48

OK, so it sounds like I need to focus on the proportioning valve for the warning light. But I will check the vacuum as you suggest.

'75

You might get the valve to center by having someone hold the pedal down hard while you bleed one of the rear calipers, that will cause an imbalance and maybe shift the switch to center.

80L48

So I have been bleeding the brakes, all 4. Would a remaining air bubble cause this imbalance and the light to come on, or is there something else that would cause it? Again, I can't find anymore leaks after fixing the initial one.

Big2Bird

The plunger is off center. Unplug the wire going to the prop valve, and watch the light go out. Brown I "think."

80L48

So will unplugging the wire help to recenter it? Or just confirm that the issue is a bubble in the lines?

Big2Bird

It will just confirm that the plunger inside is off center.

80L48

Thanks, hoping to work on it today or tomorrow. Will post the fundings

Update: well after confirming booster and proportional warning light are functioning correctly, I went back and bled all 4 wheels again, some air bubbles did come out. Test drove and no more warning lights and brakes seem right!

Thanks for all the inputs and education!

NewbVetteGuy

It was really educational to see the group troubleshooting on this! Thanks folks!


My understanding is that squishy pedal is always something in the hydraulic system and most often air bubbles. A nice hard pedal that requires you to push hard on the brakes indicates vacuum booster issues (as does the RPM hunting / unsteady idle).


Adam

DUB

You ARE correct.....a soft/spongy brake pedal has to do with the hydraulics of the system

Air bubbles in the system is one cause for a 'squishy' brake pedal. Sludge build up in the brake system due to lack of maintenance...which.... displaces what should be good brake fluid can also cause for a soft/spongy brake pedal.

Crap getting on your brake pad friction surface or rotor also can cause for lack of grip...thus giving the impression that the brakes are not grabbing correctly also. I know this is slightly diverting down another path of brake diagnostics. Also...and it is only because I have experienced it....getting the correct type of brake pad lining material can effect how responsive your brakes are also. They all somewhat all link together to give good brakes.

DUB