i got a mushy *** pedal and the brakes wont hold. i did everything i can think of. i am having no luck at all with this.

if anyone has any thing they can add please do.

 

Mushy pedal generally means air trapped in brake lines. Is the master cylinder new? was it bled before being installed? There are a few ways to bleed masters on the car but they either require a pressure bleeder or two people. Have you checked the calipers for a stuck piston? Is it rear drum? Are the rear drum brakes assembled correctly? A few things to look at.

 

check for tiny leakes in the lines.

 

ok yes i changed the master and i bench blead it. everything that i can think of is new.

 

You say the brakes wont hold. Do you mean that you cant hold the vehicle at a stop in gear? Or that the pedal goes to the floor when you stay on it?

 

in park or in drive when i hit the gas the peddle drops.

 

You said when you hit the gas the brake pedal drops? Did you mean brake pedal instead?

 

Is there a good vacuum at the check valve going to the power booster? With the car in park, check to see what happens to the vacuum at the check valve when you accelerate the motor a tad. If the vacuum stays solid when accelerating the engine, I would gravity bleed the brakes next and then see what happens. Sounds more like a vacuum problem then a brake fluid problem.

 

^^^ I was thinkin' the same thing about the vacuum issue, but wanted to be sure the post wasn't a typo first. Though I would figure the pedal would be harder to push in that situation. Does the system maintain pressure when the engine is off?

 

i thought if it was a vac issue that the brake peddle would get hard also.

yes the car does hold pressure when it is off but if i hit the brake when the car is off the vac pressure drops to 0.

 

What happens when the engine is off and you step on the brake pedal? Is it solid feeling right from the start or do you have to pump the pedal a few times to get the pedal to height? What happens when you bleed the calipers/wheel cylinder? Does a steady stream of brake fluid come out when the pedal is depressed and you open the bleeder valve? With the brake pedal up no pressure on it, engine off, does any brake fluid trickle out of the bleeder valve on every caliper/wheel cylinder when you crack it open?

 

with engine off there still is a weak *** peddle. pumping it makes it a hair better.
yes when i bleed them i get a great stream.
yes i do get a trickle lol.

 

My instincts are pointing me back to the master cylinder. I could be wrong but perhaps it still has air in it? It doesn't sound like a vacuum issue. The lines obviously have fluid in them what with your trickle and all (sorry but that's too funny) so the only thing left is the master cylinder since you said all else is new.

 

Did you replace the rubber lines? They wear over time, allowing the rubber to expand, thus the fluid pressure never reaches the calipr because the pressure expanded the rubber line instead.

 

In this case a trickle is a good thing for your brakes. Your lines are full of fluid as Gearhead points out. Did you replace the copper sealing washers that go on in between the brake hoses and caliber housing? Are your wheel cylinders showing signs of leaking?

I would get a small plastic bottle with a rubber hose that fits tight over the bleeder valve. Crack the bleeder open, install rubber hose on the end of the bleeder other end in the plastic bottle to collect the brake fluid that drips out. Gravity bleed all 4 wheels for 20 minutes or so each. Fill the MC as needed. With the engine off, your brake pedal should be very firm. With a weak pedal it sounds like you still have air in the lines or a leak in the system somewhere.

 

yes i have SS braded lines.

 

The pedal drops when you hit the gas? Not when you start the car? Thats an odd problem. Check the vacuum line to the booster carefully. Did this problem start after you replaced the master cylinder? Pull the vacuum check valve from the booster and listen for it to suck air. It should hold vacuum with the engine off. If not you may need to replace the check valve. Do you hear the sound of sucking air under the dash with the engine running or constantly when pressing the brake? The booster could be leaking.
Have you tried pumping up the brake pedal with the engine running? You may have excessive travel in a caliper/cylinder. You probably just have alot of trapped air in the system. The increased pressure provided by the booster is compressing the air alot more than you can do with your leg.
You need to diligently bleed the brakes until the pedal does not pump up at all with the engine off. The pedal without boost needs to be solid and right at the top from the first push.

 

what if i eliminate the rear brakes.

 

Bleeding brake lines can be a PITA. On C3 Vettes it is a real PITA and the gravity bleed method works best on that system, IMO. I catch the brake fluid that trickles out during gravity bleeding, other just let it fall on to the ground and clean it up afterwards.

I would keep the back brakes in use during your troubleshooting. You just might create a whole different problem then what you have now in your brake system.

 

I would not recommend eliminating your rear brakes. Your missing something thats staring you right in the face. I suspect that you havent properly bled your brake system. With difficult systems, or if I have replaced a master cylinder and air has become trapped between the master and the PV, I use my pressure bleeder. It will remove any trapped air in the system. I still dont know whether your rear brakes are disc or drum. BTW, search this forum for issues regarding SS brake lines. They may not be all that theyre cracked up to be.

The third gens gravity bleed very well as all brake lines are below the master cyl.

 

I'd go with Doc's advice, he seems pretty much on the ball with all his posts that I've seen. Bleeding brakes is never an enjoyable thing, keep the reservoir topped off and let physics do their thing.