Master cylinder problem??

[3800SII]

oK... BEFORE I dismantle this unit and put a new one on. I just wanna make for sure that it is the culprit.... Here is how it went!

Heard a chattering noise on the drivers side front. Turned out that the anti-rattle clips were put in backwards. This caused the brake rotor to be scored badly, and worn one side of the pad down to the metal. I changed the pads and resurfaced the rotor. I forgot to take the cap off the MC and pressed the calipers inwards with a C-clamp, but after assembling the brakes I also forgot to set the brake pedal while the engine was off. I immediately noticed that the brakes were now royally spongy.

The brakes are full Autozone Ceramics, and the rotors are slotted and drilled. Before the screw-up I could stop on a dime. Now it takes more brake pedal to stop the car and the braking is too soft for my tastes. The pedal can go about halfway to the floor if I press it hard. I believe that the pedal should hold firmly
if the engine is on and your foot stays on it. Should not go to the floor...

I took the car to a shop and the mechanic told me that the master cylinder was bad. This is just a rare occurrence of failure. There are no leaks anywhere. That was the only thing it could be. I got quoted $150 to do the work, and the part was $80 from AZ. I hope to replace it myself, but I am leary about screwing with it if I cannot possibly rule out other factors like possible air in the system, ABS system, proportioning valve, etc. There are no DTCs with the vehicle nor ABS problems. Should I try to bleed the system before I take it out?

Aaron GTR and friends what do you think?

[AaronGTR]

... you asked for me by name, that's funny...


Well, I don't think leaving the cap on when pressing the pistons in will damage the master cylinder. It's probably better to take it off and it is easier to press the pistons in without that resistance. I've done it both ways before though. There has to be some way for air to get in and out of the reservoir because as your pads wear down over time the pistons sit further out and the fluid level gets lower meaning it has to be able to suck air in as well.

Have you tried bleeding the lines? It is possible that the master cylinder went bad, but I'd try bleeding the lines first and seeing if you can't get it to build normal pressure before going to the trouble of replacing the master cylinder. Because after you do that you have to bench bleed it and then bleed the proportioning valve and ABS unit as well and it's a lot more work.

[mfuller]

Bleed the system and change to semi-metallic pads. Ceramics are not the way to go for strong braking performance. Ceramic pads are for low dusting and long wear.

[AaronGTR]

Yes, I agree with that also. Didn't even notice the part about using ceramic pads. Cross drilling and slotting on stock size rotors won't do you any good, and you'll actually lose contact surface area with the pad from all the extra metal that is missing. That along with hard ceramic pads could certainly be affecting your stopping power. I'd go with carbon metallic pads and slotted only or plain face rotors.

[Malibu Glow]

Did you bother to pump up the brakes after you replaced the pads and such? If you did not then that's why the pedal is mushy. You pushed the pistons back into the calipers which relieves the pressure in the lines, which means the pads won't be close to the rotor the first time you touch the brakes, there'll be a gap and in order to take up the gap you need to pump up the brakes till the pedal is rock hard with the engine off, then see how the pedal feels.
Oh a better way to do what you did with pushing the piston back into the caliper would be to use a brake hose clamp on the hose near the caliper and open up the bleeder screw to remove the fluid in the caliper rather than send it back into the master cylinder. You might have sent some debris up to the master cylinder and caused a problem but I'd suggest pumping up the brakes first to see if you get a firm pedal.

[dcuballa]

Well if he sent any debris back it would have made its way to the abs unit instead. I had this same issue and after auto bleending all the brakes two and three times for good measure and replacing the master....I ended up replace the abs control unit up on the driver side under the battery. To be honest I cant tell you that IT was the culprit because like I said I have basically replaced everything new master, new abs, new stainless lines, but the pedal is back to where it once was.

[3800SII]

Originally Posted by dcuballa

Well if he sent any debris back it would have made its way to the abs unit instead. I had this same issue and after auto bleending all the brakes two and three times for good measure and replacing the master....I ended up replace the abs control unit up on the driver side under the battery. To be honest I cant tell you that IT was the culprit because like I said I have basically replaced everything new master, new abs, new stainless lines, but the pedal is back to where it once was.

You guys are great thanks for the replies! I hope it is not the ABS unit, but what can I do?

[3800SII]

Originally Posted by AaronGTR

... you asked for me by name, that's funny...


Well, I don't think leaving the cap on when pressing the pistons in will damage the master cylinder. It's probably better to take it off and it is easier to press the pistons in without that resistance. I've done it both ways before though. There has to be some way for air to get in and out of the reservoir because as your pads wear down over time the pistons sit further out and the fluid level gets lower meaning it has to be able to suck air in as well.

Have you tried bleeding the lines? It is possible that the master cylinder went bad, but I'd try bleeding the lines first and seeing if you can't get it to build normal pressure before going to the trouble of replacing the master cylinder. Because after you do that you have to bench bleed it and then bleed the proportioning valve and ABS unit as well and it's a lot more work.

Ok... I wish that I had more time to taclkle bleeding the lines, but I will go back to the shop and see if they can do it for me. I still have my firebird on jackstands in the garage. I will go on Monday.

[3800SII]

Originally Posted by Malibu Glow

Did you bother to pump up the brakes after you replaced the pads and such? If you did not then that's why the pedal is mushy. You pushed the pistons back into the calipers which relieves the pressure in the lines, which means the pads won't be close to the rotor the first time you touch the brakes, there'll be a gap and in order to take up the gap you need to pump up the brakes till the pedal is rock hard with the engine off, then see how the pedal feels.
Oh a better way to do what you did with pushing the piston back into the caliper would be to use a brake hose clamp on the hose near the caliper and open up the bleeder screw to remove the fluid in the caliper rather than send it back into the master cylinder. You might have sent some debris up to the master cylinder and caused a problem but I'd suggest pumping up the brakes first to see if you get a firm pedal.

Right... Like I originally posted. I did not press the brake pedal down after finishing the job. Dumb mistake. I turned the car on and noticed the pedal going to the floor. I then turned the motor back off and pumped the brakes. Worked better but the pedal has been mushy ever since.

[3800SII]

Originally Posted by mfuller

Bleed the system and change to semi-metallic pads. Ceramics are not the way to go for strong braking performance. Ceramic pads are for low dusting and long wear.

Well... I had ridiculously excellent braking after the pads and rotors were originally changed. I will change back to semi metalics assuming the bleed system does not work. BTW does that bleeding have to come at all four wheels and the ABS unit? Or just the four wheels?

Hey everyone! I forgot to mention that the drivers side caliper has a slight cliking noise to it. I only hear it when the pedal is fully engaged about 3/4 of the way to the floor. If the car is parked you can hear it well. Could the caliper be the culprit
instead of the MC? Still...nothing is leaking . The clicking began immediately after the botched brake job...

[dcuballa]

Is the click only at lower speeds...if so I still have this issue....it has not be resolved but I do not feel it is the caliper as I have taken down both sides every few months and checked the specs to make sure that the driver side wasnt engaged when I left off.

[AaronGTR]

Originally Posted by 3800SII

Well... I had ridiculously excellent braking after the pads and rotors were originally changed. I will change back to semi metalics assuming the bleed system does not work. BTW does that bleeding have to come at all four wheels and the ABS unit? Or just the four wheels?

Should only have to bleed the lines at the calipers. If you haven't disconnected the lines at the master cylinder or ABS unit then there shouldn't be any air in there.

[Malibu Glow]

Originally Posted by 3800SII

Right... Like I originally posted. I did not press the brake pedal down after finishing the job. Dumb mistake. I turned the car on and noticed the pedal going to the floor. I then turned the motor back off and pumped the brakes. Worked better but the pedal has been mushy ever since.

Do you have rear disc brakes on this car? If you have drum brakes adjust up the rears to improve pedal feel. Now a bad master cylinder would make the pedal go all the way to the floor not half way.

By the way how far down is the pedal wih the car running? Is it half way, a little more than half? I've heard some say that ceramics can give a softer pedal feel which might be the case. Ceramics are a little overated for street use anyway IMO, a good set of semi-metallics will do the job well.

[3800SII]

Originally Posted by Malibu Glow

Do you have rear disc brakes on this car? If you have drum brakes adjust up the rears to improve pedal feel. Now a bad master cylinder would make the pedal go all the way to the floor not half way.

By the way how far down is the pedal wih the car running? Is it half way, a little more than half? I've heard some say that ceramics can give a softer pedal feel which might be the case. Ceramics are a little overated for street use anyway IMO, a good set of semi-metallics will do the job well.

Thanks for the reply! The pedal can go almost all the way to the floor if I push really hard while the engine is running. The brakes are always engaged, but the pedal travel and "mushiness" are my problem. My GAGT has discs all around.


I hear ya on the ceramics, but once again I had no problems whatsoever with them when they originally went on my car with and without the slotted+drilled rotors.

[3800SII]

Originally Posted by AaronGTR

Should only have to bleed the lines at the calipers. If you haven't disconnected the lines at the master cylinder or ABS unit then there shouldn't be any air in there.

You da man Aaron. Thanks again for the good info.

[3800SII]

Originally Posted by dcuballa

Is the click only at lower speeds...if so I still have this issue....it has not be resolved but I do not feel it is the caliper as I have taken down both sides every few months and checked the specs to make sure that the driver side wasnt engaged when I left off.

I almost forgot about this one... The clicking is really a "creaking" noise. I did a search on this site, and discovered that it is a problem common to N-body cars.
I am going to push the caliper piston out and spray some lubricant under the boot to see if that helps. I saw a post where somebody tried this instead of that GM grease and they said it worked. If it does not work then I will replace the caliper since this is pretty cheap to do...

[AaronGTR]

Make sure you greased up the caliper pins really well too, and I usually put a little copper brake anti-seize lube on the piston face where it touches the backing plate of the pad, as that sometimes makes a creaking noise. Hopefully that does the trick. Learned that one from my dad.

[3800SII]

Originally Posted by AaronGTR

Make sure you greased up the caliper pins really well too, and I usually put a little copper brake anti-seize lube on the piston face where it touches the backing plate of the pad, as that sometimes makes a creaking noise. Hopefully that does the trick. Learned that one from my dad.

Well... I made everything worse! I tried to bleed the brakes today on my own. Now the caliper is making a grinding noise badly. Wish me luck, a tow truck is on the way for the shop

[3800SII]

Originally Posted by 3800SII

Well... I made everything worse! I tried to bleed the brakes today on my own. Now the caliper is making a grinding noise badly. Wish me luck, a tow truck is on the way for the shop

Well... We replaced the master cylinder. I paid the guy $75 to do the work at another shop. He bench bled the MC, and he bled the four wheels. I still get the same mushy pedal.

I went home and changed to carbon metallic pads. The problem is now worse Now I have a new MC and new pads with miserable braking power. I have to use much more foot pedal to get the car stopped. This is friggin aggravating!!!

WHAT THE HECK ELSE IS LEFT??? Should I have them follow the procedures for bleeding the ABS system and proportioning valve?

[2000 GT Coupe]

I would say yes bleed the abs if the MC was changed that would introduce air into the abs unit.