[oldfella1962]

I recently bought a 1986 Corolla. I have plenty of brake fluid, and put new front pads on today.

The brakes work, but you have to press the pedal pretty far down.

Every now and then (at an intersection for example) the car will slowly creep forward even with the brake pedal fully pressed. I then must use the parking break to keep the car from creeping!

How can the brakes work intermittently?

[Starguard]

Sounds like you have air in the lines. They may have to be bled!

Either that, or a seal in the Master Cylinder has gone bad. Take a look around the brake lines feeding into the proportioning valve and tell us if you see anything leaking anywhere!

[oldfella1962]

Sounds like you have air in the lines. They have to be bled!

Either that, or a seal in the Master Cylinder has gone bad. Take a look around the master cylinder and tell us if you see anything leaking anywhere!

So this causes the brakes to work sometimes but not at others? This is the part that confuses me. Why do they stop the car briefly, but slowly fail when you depress the pedal for a long time?
Is this where the "air in the lines" comes into effect?

Regardless..."bleeding the brakes." Could you refresh my memory on this procedure? It's been a couple of years since I did this.

[Uncle Albert]

Someone correct me if I get this wrong, but I think all you do is start with the wheel furthest from the master cylinder, loosen the bleeder screw and have someone gently pump the pedal until nothing but fluid comes out (use something to catch the fluid, obviously[/i]) then tighten that bleeder screw. Top off the master cylinder reservoir, then repeat the same procedure at each wheel.

I've never really had to bleed the entire system. Mostly just bled out one line when I knew I'd let some air in right near the wheel. But I got really good at bleeding out the hydraulic clutch linkage on my old CJ.

[Starguard]

So oldfella, How did it turn out?

[oldfella1962]

Super! Thanks for asking. All evidence points toward a brake master cylinder.
They are about 60 dollars after turning in the core.

So for now, all I have to do is pump the brakes periodically to keep the pressure up for when I do need to sit at an intersection.

I have no problem driving, but my son is not very experienced driving "not so responsive" vehicles. My Army training is really paying off!

So come payday, I will get the master cylinder + a new exhaust pipe.
We don't have "emissions" testing in GA, so I'll get someone to run a pipe from manifold to muffler, foregoing a catalytic converter completely.

[Starguard]

Originally Posted by oldfella1962

Super! Thanks for asking. All evidence points toward a brake master cylinder.
They are about 60 dollars after turning in the core.

So for now, all I have to do is pump the brakes periodically to keep the pressure up for when I do need to sit at an intersection.

I have no problem driving, but my son is not very experienced driving "not so responsive" vehicles. My Army training is really paying off!

So come payday, I will get the master cylinder + a new exhaust pipe.
We don't have "emissions" testing in GA, so I'll get someone to run a pipe from manifold to muffler, foregoing a catalytic converter completely.

[oldfella1962]

Turns out it's the "boost" sitting right underneath the master cylinder.
Incredibly easy part to replace. I also have a bud who works at Auto Zone and gets me discount parts.

Other than that, it's a good car.

[Elwood]

It's called a Power Brake Booster. It's what make power brakes, well, power brakes. It's the mechanical assist for the brakes like the power steering pump is the mechanical assist for the steering system.

[oldfella1962]

It's called a Power Brake Booster. It's what make power brakes, well, power brakes. It's the mechanical assist for the brakes like the power steering pump is the mechanical assist for the steering system.

I see....but if the power brake booster is just a mechanical assist (making it easier to apply the brakes) then why do you gradually lose braking power once the car is already stopped?

Just a "theoretical" question - I am a maintenance man myself, but with electronic military equipment. I know less than jack-shit about cars.

[Elwood]

Originally Posted by oldfella1962

I see....but if the power brake booster is just a mechanical assist (making it easier to apply the brakes) then why do you gradually lose braking power once the car is already stopped?

Just a "theoretical" question - I am a maintenance man myself, but with electronic military equipment. I know less than jack-shit about cars.

The Power Brake Booster operates in conjuction with a valve to use vacuum pressure produced by the engine to amplify the force you use when pressing the brake pedal. The vacuum system is probably damaged. It could be anything from a crack in one of the rubber vacuum hoses to the Booster itself malfunctioning.

When it comes to the brake system, it's best not to take chances. Also, since it's a 1986 model car, I'd check all of the little rubber vacuum hoses and replace any that show any signs of age or wear. Vacuum tubing is dirt cheap. Take a piece with you into the parts house and buy a five foot piece of the same size Then just cut it to length as needed.

[oldfella1962]

That makes sense! My son says he hears a hissing sound when the brakes are slowly losing pressure. With my hearing loss, I could not of course.
I will do the rubber hose thing first. Thanks!

[Starchaser]

Originally Posted by Uncle Albert

Someone correct me if I get this wrong, but I think all you do is start with the wheel furthest from the master cylinder, loosen the bleeder screw and have someone gently pump the pedal until nothing but fluid comes out (use something to catch the fluid, obviously[/i]) then tighten that bleeder screw. Top off the master cylinder reservoir, then repeat the same procedure at each wheel.

I've never really had to bleed the entire system. Mostly just bled out one line when I knew I'd let some air in right near the wheel. But I got really good at bleeding out the hydraulic clutch linkage on my old CJ.

Dont open the bleeder untill after the brakes are pumped up. Otherwise you just suck air into the lines everytime the brake pedal is let up.