Is my brake master cylinder bad?

Question

hopfully there is someone who can help me with this question. I have a 99 chevy malibu, 3.1 v6. I replaced the front brake calipers. When I started to bleed them, I could not get the fluid to pump to the bleeder valve on the caliper with enough pressure to bleed it. The fluid would only come out slowly no matter how hard you pumped the brakes. So I went ahead and hooked the rubber line to the bleeder screw and dropped it into my containor of brake fluid. After pumping the breaks for aprx 10 minues, I had barely even pumped any fluid out at all. Still lot's of air. It just isn't putting enough pressure to the fluid to get it to come out fast enough to get all the air out. The brake pedal never gets any firmer no matter how long you pump it. This holds true for both sides. Before changing the calipers, I had noticed a cpl of times while driving that the pedal seemed to be going down farther than normal. That is why I originally put new brakes and calipers on it.

(99 malibu) ok, I tried bleeding the brakes again. I opened up the bleeder on the rear passenger side, took off the master cylinder resovoir, and waiting for it to drip, 1 hour and there was still no drip. I hooked a hose over the bleeder valve and dropped it into a bottle of brake fluid. pumped brake about 50 times and still no brake fluid coming out of the bleeder. Just to see what happens, I tried the front, it seemed to be working, pumping the air out. When I didn't see anymore bubbles, I tightend the bleeders. I then went back to the rear again, and I still couldnt get any fluid to pump out. I just had a motor put in the car, alt, alt bracket, 2 calipers, thermostat, hoses, I really don't want to have to pay $90 for a master cylinder unless I'm pretty sure that is what it is. Thanks for all your help. It's 104 today here in memphis, And listening to you guys sure beats me guessing out in the heat.

meant to say that I took the cap off the master cylinder resovoir when I was trying the gravity bleed, I didn't actually take off the resovoir. And I did put the cap back on before trying to actually bleed the brakes.

I just checked, brake warning ligt is not on. I have also tried bleeding the with 2 people as well, the old fashion way, but i've been told by a few people that the rubber line and bake fluid bottle is just as, if not more effective.

Answer 1

Sounds like you probably did the wrong repair, so now you still have the original problem plus some problems that you created your self.
Start from the top by getting all 4 wheels off and inspecting the whole system. I don't remember if a 99 malibu has rear disk or drum, i think drum. The most common reasons for excessive pedal travel, the first being the rear brakes out of adjustment.Adjust rear brakes with the star wheel, you want enough drag to give the drum a good spin and only getting about 1/2 to 3/4 of a revolution out of it when you let go of it. The next likely cause of excessive pedal travel is a leak in the system, at this point its most likely the rear wheel cylinders.
If you've now determined the brakes are properly adjusted and you have no hydraulic leaks, open all 4 blead screws and gravity bleed tell you see fluid dripping out all 4. Then close and bleed all the way around starting at wheel farthest away from master and working in order to closest.
You may have been taking alot of air into the sys when you had a leak or durring the repair so bleeding it may be tough, but the gravity bleed first should help.
If you get this far and still have the same problem clamp off all 4 of the rubber brake hoses. Now you should have a hard pedal even if there is still air in the system, if not it should be a bad master(usually a bad master gives you a good pedal right at first then slowly drops.) If the pedals hard hold it down then have an assistant begin removing the clamps on the hoses, again starting furthest from the master and working closer in order. When you remove a clamp at a certain wheel and the pedal drops you just found the leak or the air pocket.

Dude don't over complicate this. Even if its white its not the space shuttle. I'm telling you, do the clamp test its saved my butt many times, and I've showed pro techs how to do it and they were thankfull.
You can buy clamps for brake hoses at most parts stores for probably 20 bucks, in a pinch you can use vice grips witha shop rag wraped around to protect the hoses. Brake Basics 101 start from the farthest point from the master and work your way back towars the master when you remove a clamp and the pedal drops you found the problem.Dont guess. TEST. Do this and get out of the heat.

Answer 2

Ok so are you doing this by yourself? This may sound insulting but I gotta ask to be sure I'm giving you the right answer so here goes. You do know that it takes two people to bleed brakes and that you dont pump with the bleeder open right?? If you pump with the bleeder open you just keep sucking more air in when the pedal goes back up. That being said....If you doing it right, your first step is to open all the bleeders for the brakes, front and rear, and let them "gravity bleed". That means just walk away for about half an hour or so and only come back to check the fluid. When you have pretty steady flow out of all bleeders close them off and pump the brakes. If the pedal doesnt get hard after a few pumps just hold it down anyway and have someone open the right rear bleeder screw for a few seconds then close it and pump the brakes up again. It sounds like you just got a LOT of air in the brakes. Even if the master cylinder was bad you would still be able to bleed the brakes you just wouldnt be able to keep a hard pedal when you were done. Kind of a long winded answer but hopefully if helps. If you want more details just send me an email or IM. Good Luck!!!

Answer 3

There are three main things that would cause your issues. One is a restricted brake line where the fluid can be forced out to the caliper when the pedal is pressed but can't release because the restriction is stopping the return of the fluid, there's no force applied after you release the pedal. Another is a stuck piston. The piston moving toward the rotor is the action caused by the fluid when the brakes are applied, but if its tight or dragging in the bore you have the same scenario as when a line is restricted. The piston can't move back so the brakes remain applied. Last is lack of lubrication on the slide rails or pins that the calipers slide on. These have to be lubed regularly or they'll rust and cause the calipers to stick in the braking position. Any one of these can result in overheating of the rotors, pads, calipers and fluid. If the fluid boils you get the pedal to the floor syndrome. Those brake hoses with the squishy ends might be a good place to start. Always helps to know what vehicle we're talking about, mileage, etc. While we now know about the Camaro , that info wasn't much help in determining what vehicle you have now.

Answer 4

That seems odd.
I doubt your master cylinder is bad.
There is a proportioning valve that blocks the flow of brake fluid in the event you have a brake line failier.

Close the bleeders.
Pump up the brakes.
Have SOMEONE ELSE open one of the bleeders WHILE you hold the pedal down.

Repeat this several times and don't let the master cylinder go dry. Otherwise you'll have to start all over.

ADDED:
Adjust your rear brakes too.

Answer 5

Get a good bleeder kit or a cleaned out oil squirt can and clean brake fluid and introduce the fluid at the bleeder on the caliper... this will force the air bubbles to rise into the master cyl. resevoir... sometimes a system has to be bled backwards to get initial pressure and then it can be bled conventional... hope this helps... oh yes...you will need a small hose to connect the can to the bleeder valve...

Answer 6

It could be either the master cylinder, or the proportioning valve, or both. Try this, press on the brake, and hold pressure. Does it continue to go down? You have either a leak or a bad master cylinder if so. Let off slightly and press again. Does it go to the floor? You definitely have a bad one if that happens. I'd change out the master cylinder first, see if that corrects the problem.

Answer 7

is your brake warning light on?.....if so....it is your proportioning valve.....it,s purpose is to regulate the flow....regulate pressure...approx. 75% front-25% rear....it also will cut off either front or rear in case of hydraulic failure...& will turn on the warning light.......if it has shut off flow to your front...you,ll never get them bled unless you center the valve first....to do this you,ll need the help of a friend.....close front hydraulic,s...pump up brake,s & hold....open rear bleeder untill light turn,s off...close bleeder.....then lessen pressure on pedal slightly....proceed to bleed front....if the light come,s back on...you must recenter the valve.....it is located aprox. 10 inch,s directly below the master.....some model,s had a 1/8 hole in the side...after centering...insert a 1/8 drill bit in the hole to keep the valve from cycling...then you can bleed as in old day,s.....don,t forget to remove drill bit when done...good luck!.......if your problem still exist,s....change master....bench bleed it first.....also change front brake hoses....they have been known to cause similar problem,s......e-mail if you need further assistance...once again.....good luck!

Answer 8

The one obvious thing I miss from your description is:
Did you fill the master cylinder reservioir?