Weak brakes

[Lani Kai]

Here are the symptoms:

-When engine is not running, the brake pedal feels firm.

-When engine is started, brake pedal is light. Giving it a few pumps makes it a bit better.

-There is a bit of play in the pedal when the engine is running.

-The brakes are weak, but not spongy. Replacing the booster improved it somewhat.

Here is what I've done to the brakes so far:

-Replaced brake booster with a remanufactured one (old one was leaking from the shell).

-Replaced brake lines with braided stainless steel lines.

-Bled master cylinder

-Bled brake lines, rear first.

What's the diagnosis?

[Matt K]

Possibly the reaction disk that goes between the master cylinder & booster fell out...happens a lot on these cars...

[Zed Head]

What do you mean by weak? The car won't stop quickly? Have you looked at the pads and shoes?

Pumping should only help if you have air in the lines. When you pump, you're just pushing more fluid in to compress the air bubbles. If pumping helps, then more bleeding is in order.

[esmit208]

Lani Kai

Just one more link in the chain, there is a check valve attached to the firewall. It is an inline check valve inserted in the vacuum hose that runs from the booster to the intake manifold. They rarely go bad but they are replaceable. Since you are looking into the brake system it wouldn't be a bad idea to replace that valve.

[Lani Kai]

Thanks for all the input. I'm going to try completely flushing out the old brake fluid first, and thoroughly bleeding it. Who knows how old the fluid in there is...

I know the reaction disc falling out is a definite possibility, although I'd like to think it isn't because the booster is a newly remanufactured unit. It's just that the contortionist stuff I have to do in the footwell to unlink the booster from the brake pedal is something I'd rather avoid.

As for the check valve, I suppose that's what I will look into replacing if the first two don't work, if it's something that doesn't commonly fail.

[5150 will]

If the reaction disc has fallen into the booster it is kind of a pain, but it's FREE. I'd look there first. If you separate the master from the booster you should be able to GENTLY move the master enough to at least see/feel if the disc has fallen in there.

[tymarbry]

It could also be a leak from the seals in your calipers also.

Seals need replaced if the calipers are leaking. Especially consider this if you live in an area with bad weather that will cause rust. Rust gets in the seals and they dont do their job. Fairly easy and cheap for a caliper rebuild. maybe like $9 for each side, just takes time.

[Lani Kai]

If the reaction disc has fallen into the booster it is kind of a pain, but it's FREE. I'd look there first. If you separate the master from the booster you should be able to GENTLY move the master enough to at least see/feel if the disc has fallen in there.

How do I see/feel if the disc has fallen without removing the booster from the car?

It could also be a leak from the seals in your calipers also.

Seals need replaced if the calipers are leaking. Especially consider this if you live in an area with bad weather that will cause rust. Rust gets in the seals and they dont do their job. Fairly easy and cheap for a caliper rebuild. maybe like $9 for each side, just takes time.

I don't have any noticeable fluid leaks, but I will look in to that. I'm in Southern California so hopefully I don't have a terrible amount of rust.

Edited March 9, 2011 by Lani Kai

[Lani Kai]

Is there anything that suggests there may be an issue with the MC, or am I correct in guessing it's probably fine? The pedal does not sink.

[TomoHawk]

My rubber hoses from the body to the calipers/cylinders were old and soft, so they would swell and even leaked a bit occasionally, which I think caused a weak feeling. I installed a set of the braided stainless hoses and it improved a LOT. I had the same issue with my DD (rear rubber hoses would swell.)

[Lani Kai]

My rubber hoses from the body to the calipers/cylinders were old and soft, so they would swell and even leaked a bit occasionally, which I think caused a weak feeling. I installed a set of the braided stainless hoses and it improved a LOT. I had the same issue with my DD (rear rubber hoses would swell.)

Yeah, I replaced the rubber lines with braided SS lines because the old ones looked pretty bad.

[Lani Kai]

Well, checked reaction disc, picked up a rebuilt MC, bench bled it, installed it, and bled the entire system (LR-RR-RF-LF), pedal felt relatively firm. Checked to make sure there were no leaks. Started up the car to induce a vacuum and now the pedal has very little resistance. Haven't taken it out for a test drive because it's dark and raining heavily, but I have a feeling it's not good.

Running out of ideas...