Master cylinder problem??

[AaronGTR]

Uh, yeah... the guy at the shop should have known this. If you disconnect the two lines from the master cylinder they probably got air in them. Those go down to the proportioning valve and ABS solenoids. That's probably why your pedal is squishy now.

If that doesn't work though, then I'd say either you have a brake line that has gone very soft, or a bad caliper.

[mfuller]

Your mechanic will need a Tech2 to cycle the valves in the ABS solenoid. At least that's the proper way to do it (so says my GM service manual).

[3800SII]

Originally Posted by 2000 GT Coupe

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

Thanks... I am taking the car back to him tomorrow with instructions on how to bleed the ABS. If it does not work well then I will spend the $$ to take it to a dealer. What a mess...

[3800SII]

Originally Posted by AaronGTR

Uh, yeah... the guy at the shop should have known this. If you disconnect the two lines from the master cylinder they probably got air in them. Those go down to the proportioning valve and ABS solenoids. That's probably why your pedal is squishy now.

If that doesn't work though, then I'd say either you have a brake line that has gone very soft, or a bad caliper.

Makes me wanna choke some folks! I told him that those really should be done, and he said that it was not necessary. I think he did not know WTF he was doing now!

Now how could I tell if the brake hose or line has gone bad? Wouldn't it just leak fluid? I placed some lube behind the caliper's piston boot and the creaking is completely gone from the driver's side... Both calipers seem to be engaging well.
Aaron please tell me what I should look for. I want to eliminate all possible variables...

[AaronGTR]

Yeah, I would say any time the master cylinder is disconnected, the ABS unit should be bleed. That's what it says to do in the manual. I think if the lines haven't been disconnected long and haven't got much air in them, sometimes you can bleed them by just cracking open the lines where they connect to the proportioning valve (following the normal bleeding procedure with someone stepping on the pedal). Not 100% sure how well that works though. It gives a procedure for bleeding the ABS unit if you don't have a tech2 to cycle the valves with... but it takes a lot longer and isn't always consistent. You have to turn the car on for like 10 seconds and off in between bleeding over and over again because the solenoids run through a test cycle every time you start the car. It's much easier to just command them to cycle with a tech2 while you are bleeding.

As for brake lines, if it's the metal lines they won't be bad unless you see rust spots on them somewhere and they look kind of wet. The rubber lines just get soft and start to expand more as they get old, and when they get really old the rubber starts getting dry and cracking. It's hard to say when they are bad. You just have to visually inspect them and see how old they look and feel. But if you want better performance and no lose of pressure, just get braided lines. They are well worth the increase in pedal feel and response IMO.

[3800SII]

Originally Posted by AaronGTR

Yeah, I would say any time the master cylinder is disconnected, the ABS unit should be bleed. That's what it says to do in the manual. I think if the lines haven't been disconnected long and haven't got much air in them, sometimes you can bleed them by just cracking open the lines where they connect to the proportioning valve (following the normal bleeding procedure with someone stepping on the pedal). Not 100% sure how well that works though. It gives a procedure for bleeding the ABS unit if you don't have a tech2 to cycle the valves with... but it takes a lot longer and isn't always consistent. You have to turn the car on for like 10 seconds and off in between bleeding over and over again because the solenoids run through a test cycle every time you start the car. It's much easier to just command them to cycle with a tech2 while you are bleeding.

As for brake lines, if it's the metal lines they won't be bad unless you see rust spots on them somewhere and they look kind of wet. The rubber lines just get soft and start to expand more as they get old, and when they get really old the rubber starts getting dry and cracking. It's hard to say when they are bad. You just have to visually inspect them and see how old they look and feel. But if you want better performance and no lose of pressure, just get braided lines. They are well worth the increase in pedal feel and response IMO.

Thanks again man. I hope to get some of this taken care of tomorrow. Having $hi++y brakes and a good turbocharger is a recipe for an insurance claim! There is no way I can hit boost and hope to stop or slow down in time with heavy traffic.

[Malibu Glow]

Originally Posted by AaronGTR

Yeah, I would say any time the master cylinder is disconnected, the ABS unit should be bleed. That's what it says to do in the manual. I think if the lines haven't been disconnected long and haven't got much air in them, sometimes you can bleed them by just cracking open the lines where they connect to the proportioning valve (following the normal bleeding procedure with someone stepping on the pedal). Not 100% sure how well that works though. It gives a procedure for bleeding the ABS unit if you don't have a tech2 to cycle the valves with... but it takes a lot longer and isn't always consistent. You have to turn the car on for like 10 seconds and off in between bleeding over and over again because the solenoids run through a test cycle every time you start the car. It's much easier to just command them to cycle with a tech2 while you are bleeding.

As for brake lines, if it's the metal lines they won't be bad unless you see rust spots on them somewhere and they look kind of wet. The rubber lines just get soft and start to expand more as they get old, and when they get really old the rubber starts getting dry and cracking. It's hard to say when they are bad. You just have to visually inspect them and see how old they look and feel. But if you want better performance and no lose of pressure, just get braided lines. They are well worth the increase in pedal feel and response IMO.

Technically air shouldn't reach the ABS unit, once the lines are opened, the lines don't loose any fluid from more than an inch away from the master cylinder, and when installing the master cylinder before bleeding the system the lines are cracked open to push air out at the master cylinder then the system is bled. I;ve never run into a situation where I had to cycle the ABS after replacing a master cylinder, I've bled the system as required at each wheel and always got a good firm pedal before the car left my shop.

3800II,
But since you've come to a point where the pedal feel is not what you are use to then a complete system bleed would be in order to bring the pedal feel back to normal.
Now what I would suggest is the next time you do a brake job, you NEED to pump up the brakes BEFORE you start the car to get the calipers pushed out and contacting the backsides of the pads.

[AaronGTR]

Originally Posted by Malibu Glow

[b][color="Yellow"]Technically air shouldn't reach the ABS unit, once the lines are opened, the lines don't loose any fluid from more than an inch away from the master cylinder, and when installing the master cylinder before bleeding the system the lines are cracked open to push air out at the master cylinder then the system is bled. I;ve never run into a situation where I had to cycle the ABS after replacing a master cylinder, I've bled the system as required at each wheel and always got a good firm pedal before the car left my shop

Um, technically you're wrong. The ends of the lines that connect to the master cylinder have a short horizontal section before they turn down, where fluid will leak out and air will get in. It might not be much, but any air in the lines will cause a soft pedal. The only way to get that air out of those lines is to loosen the lines connections and bleed them at the proportioning valve, not the master cylinder. When you build pressure in the master cylinder it will push that air down the lines. The lines are small enough and the brake fluid has enough viscosity to do that. You have to bench bleed the master cylinder when you install it, but once you hook those two brake lines back up too it, the only way to get the air out is down system from the master cylinder. If you were to leave the air in the lines and drive the car long enough, the air would eventually get to the ABS unit as well, but just being in the two supply lines to it will make the pedal soft.

[Malibu Glow]

Air will always find the quickest path out and by bleeding off at the master cylinder you're not forcing the air further down the system. Since the air would be so close to the master cylinder it will be quicker to bleed the air out from there, then the rest of the system can be bled, I've never had a problem bleeding this way.

[3800SII]

Originally Posted by Malibu Glow

Air will always find the quickest path out and by bleeding off at the master cylinder you're not forcing the air further down the system. Since the air would be so close to the master cylinder it will be quicker to bleed the air out from there, then the rest of the system can be bled, I've never had a problem bleeding this way.

Well... after a month of figuring the brakes would never be worth a damn again until I take it to a professional, the system has somehow returned to normal again. I wonder if the constant starting of the vehicle somehow got the air out of the system. I won't complain because I got much, much better pedal. It is just weird how the problem seemed to fix itself.

[AaronGTR]

Originally Posted by Malibu Glow

Air will always find the quickest path out and by bleeding off at the master cylinder you're not forcing the air further down the system. Since the air would be so close to the master cylinder it will be quicker to bleed the air out from there, then the rest of the system can be bled, I've never had a problem bleeding this way.

Except that when you apply pressure the air won't move backwards. The air is forced down the lines as soon as you step on the pedal, so you can't bleed them at the master cylinder connections. You have to do it at the lower end of the lines. Says so in the manual, and that's how I had to do it to get rid of all the air in mine.