Master Cylinder Going Bad?

[ElaineZ]

Ive noticed a couple of times in the past a brake light coming on. Then, it stopped. I figured it had something to do with my replacing the rear brakes. Anyway, it started again (right about the time I said I wasnt having any Z troubles......). In fact, when I pulled into a parking lot the pedal went to the floor, (I began frantically pumping)the Z slid several feet on the dirt, before touching the wall (had to do some funky steering there....but at least it was just the bumper). Im beginning to think the Master Cylinder is going out, as I had similiar troubles in another car. Anyway, if Im off base, please steer me right. If on target, how can I check for sure? What about Vaccuum on this? I know nothing to zilch about brake systems.

Thanks!

[Bambikiller240]

Sounds like you are low on brake fluid for some reason. Probably a leak somewhere.

Could be a M/C, Caliper, Rear Wheel Cylinder, brake hose, almost anything.

Fill the Master cylinder with fluid, pump the brake pedal for a while and then look under the car and at each component of the brake system searching for puddles, wet spots, etc. to help narrow down the location of any leak(s).

[ElaineZ]

Sounds like you are low on brake fluid for some reason. Probably a leak somewhere.

Could be a M/C, Caliper, Rear Wheel Cylinder, brake hose, almost anything.

Fill the Master cylinder with fluid, pump the brake pedal for a while and then look under the car and at each component of the brake system searching for puddles, wet spots, etc. to help narrow down the location of any leak(s).

Thanks! I have checked for leaks and cant find one...that is Ive done some feeling around..nothing wet, didnt get in depth cause it wasnt low on fluid... I can take the tires off tomorrow and check the hoses. When I pump the pedal it 'builds up'... which made me sort of think of vaccuum...? No? Wrong? Thanks!

[Ricklandia]

If pumping the brakes helps "build up" the pedal, it might be something as simple as air trapped in the lines. Bleeding the brakes will cure that IF that's what it is. However, if your pedal went straight to the floor as you describe, I'm betting it's a more serious issue. If the booster goes bad, you wont lose brakes, you'll only lose POWER brakes. You say the car slid several feet? Sound like the rear brakes are fine and the trouble is more likely with the FRONT brakes. If you havent lost fluid (esp. in the front resevoir), then I'm think it's likely the master cylinder. I don't know if you can get rebuild kits for master cylinders any more, but I wouldn't monkey around with a problem like this. If you suspect it might be the master cylinder, one way to test is to pump till you have a good pedal, then hold it there. If the master cylinder o-rings are bad internally, the fluid will seep around them and you will start to lose pedal after a while. I lost the front brakes on my GTO once, skidded right thru a 6-lane intersection. Not getting "T-Boned" was a miracle, but I wouldn't want to roll those dice again.

[ElaineZ]

Master Cylinder is exactly what Im thinking. I experienced pretty much the same problem in an Oldsmobile about a year ago. Like you, Im not going to check chances, again. And Im not driving it... too many steep grades here.

Thanks for your feedback. If it will clear up, Im going to go out and look around the M/C... Thanks again!

[Bruce Palmer]

Not losing fluid you say? If fluid is not leaking out of the closed system then you've more than likely lost seal inside the master cylinder not allowing fluid to be "pushed" into the front or rear brakes.

Good preventive maintenance is to completely bleed your brake system once a year of all old fluid and contaminants. Your over all brake system will last much longer.

Many times when fluid is being lost but you can't tell where, it is leaking down the inside of the firewall leaking around the seal in the back of the MC turning carpet and padding into a mess.

[beandip]

Plus the brake fluid will damage the vac booster.

[Bambikiller240]

Many times when fluid is being lost but you can't tell where, it is leaking down the inside of the firewall leaking around the seal in the back of the MC turning carpet and padding into a mess.

Brake fluid shouldn't be able to get to the firewall due the vac booster being between the BMC and the firewall. Of course, if the BMC leaks enough to fill the booster 1/2 full. then fluid could get to the firewall.

[Alan Pugh]

This happened to one of my cars when I was much younger, and the guy at the brake place called it bypassing.

My mastercylinder had a small section of corrosion in the bore and as the seal went over this area of corrosion the fliud would bypass the seal letting the pedal go all the way to the floor. It doesn't happen all the time but gets more and more frequent as time passes.

Hope this helps

Alan.

[Bruce Palmer]

Carl,

I was visualizing the manly "Armstrong" brakes on the 510 when talking about the firewall escape route. Sorry lost my head..... and something else.... er, can't remember what......

[Bambikiller240]

No worries Bruce. When I was composing my first post, I initially wrote something similar, then remembered it was the clutch master that I had seen leaking fluid all over the inside of the firewall on one of my Z's owned in the 70's.