dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
1503
share rss forum feed

Valkyre
Premium,ExMod 2002
join:2000-12-25
Valhalla

Bad Master Cylinder?

I was wondering if it's possible that I need to replace the brake master cylinder? Or maybe I can get away with bleeding the brakes?

Car is 1972 Chevy Camaro disc/drum brake system.

About two weeks ago, I noticed that when I pressed down on the brake pedal, I heard a funny sound. Almost sounded like air. Sort of like a bellows. If that makes any sense. The pedal also traveled down further than normal until the brakes would start to apply. I checked the fluid in the master cylinder. It was slightly low in the larger of the two reservoirs. Also, it was clean and not rusty. So it wasn't lack of fluid. I tried pumping the pedal to see if it would help. Same thing. I also tried applying the brakes while the car was in reverse. Didn't help. The problem started to get worse. The car can stop. But, it will not brake hard, if I had to make a panic stop. The pedal is not going all the way to the floor, but it stops less than half an inch above it.

This morning, when I applied the brakes for the first time, the red "brake" light came on, on the dash and stayed on the whole time the car was running. This afternoon at start-up, the light was off.

Last time the brake master cylinder was replaced was back in 1989. Do you think that is what is causing this? Or could there just be air in the lines. Thanks for any help.
--
Certainty of death. Small chance of success. What are we waiting for? - Gimli


Epikos
Surpass the Usual or Ordinary
Premium
join:2003-07-27
Hillsboro, OR
I'm having a similar problem in my 89 toyota pickup. My uncle was looking at the last brake job on the truck and noticed everything but the drum shoes were replaced and suggested maybe I needed rear shoes. Apparently the rear brakes account most of the "feel" of the pedal.

I haven't had time to check, but maybe your excessive pedal travel could be something as simple?

Cheers,
Epikos
--
I refuse to have a battle of wits with an unarmed person!


sdgthy

@optonline.net
reply to Valkyre
Typically, if the MC is bad, the pedal will tend to fall when you're stopped and holding pressure on the pedal. Although, if the pedal is going as low as it sounds, the seals in the MC may now be ruined.

A leaking rear cylinder is more likely. Check the inside of all the tires for any signs of leakage.


CurtesyFlush
Bababooey, fafafooey, tatatoothy.
Premium
join:2002-08-23
Fontana, CA
kudos:2

1 edit
reply to Valkyre
Does the idle speed stumble or otherwise worsen? When you apply the brakes I should probably add.
--
Life Member, NRA and CRPA.

Valkyre
Premium,ExMod 2002
join:2000-12-25
Valhalla

1 edit
Nope. No problem with the idle when the brakes are applied.

To the anon poster, thanks! I'll check around the tires to see if there is any leaking fluid.


jsolo1
Premium
join:2001-07-01
reply to Valkyre
Most (all?) vehicles have a proportioning valve. The design of the brake system is such that the front start grabbing after the rears have grabbed a certain amount - function of the proportioning valve.

Unlike disc brakes, drum brakes don't automatically self adjust [correctly]. As the linings on the shoes wear, the pedal height gets lower and lower before the brakes start to grab.

Have someone knowledgeable look at the car. Brakes serve a critical safety function.
--
Insanity is living in a state of disillusion.

fixrman
Premium
join:2003-02-10
Hatboro, PA
Reviews:
·Verizon FiOS
reply to Valkyre
Sounds to me like you have a leak somewhere, most likely the rear wheel cylinders. The brake light comes on when a rod inside the proportioning valve tilts to one side, indicating a loss of pressure on one side that is disproportionate to the pressure on the other side.

Resist the temptation to just bleed the brakes. Cars are a lot of fun, but no fun at all when they can't stop. You are toying with possibly a dangerous, imminent brake failure. Get the system checked out as soon as possible; don't keep driving it.

The car is old enough at this point that the entire system should probably be overhauled, unless calipers, hoses have been replaced recently. Those rubber components break down from heat and contaminants and age. I'd take a real good look at the master cylinder as well.


Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
kudos:18
reply to Valkyre
said by Valkyre:

I was wondering if it's possible that I need to replace the brake master cylinder? Or maybe I can get away with bleeding the brakes?

Car is 1972 Chevy Camaro disc/drum brake system.

About two weeks ago, I noticed that when I pressed down on the brake pedal, I heard a funny sound. Almost sounded like air. Sort of like a bellows.
The funny air sound can be the Power Brake Booster leaking. They have a rear seal and do go bad with age.

I suggest taking the car to a trusted mechanic.

Regards,

Doctor Olds
--
What’s the point of owning a supercar if you can’t scare yourself stupid from time to time?

fixrman
Premium
join:2003-02-10
Hatboro, PA
Reviews:
·Verizon FiOS
That was my first thought as well. I discounted it because the Brake light came on, and he is complaining that the pedal is low.

A leaking booster will not cause either of these things.

A master cylinder that is bypassing internally might, and of course so would a leak. That is not to say that he doesn't also have a booster problem, but I don't belive it to be the root cause.

In any event, he does need to have it looked at by someone who is trained.


Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
kudos:18
said by fixrman:

That was my first thought as well. I discounted it because the Brake light came on, and he is complaining that the pedal is low.

A leaking booster will not cause either of these things.

A master cylinder that is bypassing internally might, and of course so would a leak. That is not to say that he doesn't also have a booster problem, but I don't belive it to be the root cause.

In any event, he does need to have it looked at by someone who is trained.
Agreed.

Another thought I had was that I've also seen the rear seal on the Master Cylinder go bad and leak into the booster housing making it go bad also. There would not be any visible fluid loss on the ground since it gets trapped in the booster housing.

Regards,

Doctor Olds
--
What’s the point of owning a supercar if you can’t scare yourself stupid from time to time?