Brakes soft AND hard problem
Thread Starter
Senior Member
Joined: Feb 2009
Posts: 874
Likes: 18
From: Brisbane, Australia
Car: 1985 Pontiac TransAM
Engine: 400SBC 24x conversion
Transmission: T700r Stage2 Shiftkitted
Axle/Gears: 2.77 9 Bolt
Brakes soft AND hard problem
Hi Guys,
Got a problem with my brakes and was hoping someone could help as I've read everything I could and can't find an explanation that fits.
Here we go:
With the car off, manually pressing the brake, and the brakes grab enough that i can't spin the wheel.
Start the car up, the first 1/4 of pedal applied is squishy/spongy, then hit is incredibly hard.
If I put all the pressure I can on the brake, I can see the master cylinder flex a little and the car will slowly come to a stop.
I turned the car off and waited an hour.
Then I went to take the hose and check valve off the booster and it was hissing (still holding vacuum)
I changed the rear drum shoes and did a full bleed on the front discs and rear drums prior to this, but didn't touch the booster.
I adjusted the adjuster to just skim the drum as per usual. I had done the brakes as the brakes did seem a bit squishy and needed a fair bit of pressure to lock up.
Now there would never be a chance of locking them up in this state.
As an added bit of info, the front reservoir may have run empty or close to empty on the first run of bleeding, but I rebled it though again.
My only thoughts are the master cylinder has gotten air in it, or there is still air in the lines, but I would think that would cause it to be spongy.
Are there any other causes of hard brakes if the booster is working?
Any ideas?
Got a problem with my brakes and was hoping someone could help as I've read everything I could and can't find an explanation that fits.
Here we go:
With the car off, manually pressing the brake, and the brakes grab enough that i can't spin the wheel.
Start the car up, the first 1/4 of pedal applied is squishy/spongy, then hit is incredibly hard.
If I put all the pressure I can on the brake, I can see the master cylinder flex a little and the car will slowly come to a stop.
I turned the car off and waited an hour.
Then I went to take the hose and check valve off the booster and it was hissing (still holding vacuum)
I changed the rear drum shoes and did a full bleed on the front discs and rear drums prior to this, but didn't touch the booster.
I adjusted the adjuster to just skim the drum as per usual. I had done the brakes as the brakes did seem a bit squishy and needed a fair bit of pressure to lock up.
Now there would never be a chance of locking them up in this state.
As an added bit of info, the front reservoir may have run empty or close to empty on the first run of bleeding, but I rebled it though again.
My only thoughts are the master cylinder has gotten air in it, or there is still air in the lines, but I would think that would cause it to be spongy.
Are there any other causes of hard brakes if the booster is working?
Any ideas?
Member
Joined: Jan 2012
Posts: 212
Likes: 75
Re: Brakes soft AND hard problem
Is the red warning light on? it sounds as if the prop valve has switched to one axle only braking.
If you have low volume and pressure coming out of one side of the prop valve this is it. This happens when you press too hard on the pedal w/ a leak and the fluid loss is too great, the valve will close off the leak side.
You can reset it, one way is too pull the switch out of the valve and manually move the vale back to center or what has worked for me in the past is too make sure fluid is in all the lines and with the cap on the master violently stab the pedal (like your going to go off a cliff!) sometime`s repeatedly is what it takes but after a few hits it will usually pop back to center.
If you have low volume and pressure coming out of one side of the prop valve this is it. This happens when you press too hard on the pedal w/ a leak and the fluid loss is too great, the valve will close off the leak side.
You can reset it, one way is too pull the switch out of the valve and manually move the vale back to center or what has worked for me in the past is too make sure fluid is in all the lines and with the cap on the master violently stab the pedal (like your going to go off a cliff!) sometime`s repeatedly is what it takes but after a few hits it will usually pop back to center.
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