CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Brakes not working properly after slamming on them

My 2003 Saab 9-3 recently failed inspection due to spongy brakes. I didn’t think they were that bad - a little soft maybe - but I figured it was possible I didn’t notice because the change was gradual. I assumed the culprit was the master cylinder, so I replaced it (thank you GM for making the simple task of removing two nuts difficult) and flushed the old fluid.

I didn’t notice a whole lot of improvement, but the car stopped well enough. Not like new, but well enough I thought. Unfortunately, the inspector didn’t think so, and he failed it again.

I took the car home and re-bled the brakes, and there wasn’t much change. Then I did the same test as the mechanic. He accelerated for about 20 ft then slammed on the brakes. He then let the car roll about 10 feet and slammed on them again. When I replicated the test, I noticed that for the second stop the brake pedal was good and firm, but the car rolled 5-10 feet further than it should have. After slamming on the brakes the first time, I couldn’t get the car to come to a jerky stop shortly afterward.

Some possibilities:

I didn’t bench bleed the master, which I didn’t realize until after I had it back in place. At that point I figured it was easier to just bleed the air out of the system (I was going to do a complete flush of the old fluid anyway) than to remove the new cylinder, bench bleed it, and re-install. Wouldn’t the full system flush remove any air that would have been in the master?

A brake hose (or hoses) might be bad. They’re original equipment as far as I know, which makes them 10 years old. But wouldn’t that mean the brakes would be spongy all the time? Why would the second stop be so much worse than the first?

I read something about vacuum hoses for the brake booster, but there was a lot of jargon and I couldn’t make heads or tails of it. I’m not lucky enough for this to be as simple as replacing a vacuum hose.

Does this have something to do with the anti-lock brake system? Do the brakes need a few more seconds to recover after the ABS has been triggered?

Anyone have any ideas?

@norasdad

Remove the master
Bench bleed it
Reinstall it
Do another complete brake fluid flush
Road test to confirm repair

New masters have to be bench bled.

No ifs ands or buts

That is the first step for you
Don’t start worrying about the ABS and other things until you do what I suggested

Good luck and please keep us posted

^ Thank you, db.
When bench bled, how does one reinstall the master cylinder without introducing air at the connections?
Is there no way to bleed an intact and tight system?

@RobertGift

Any time you crack open a brake hose/line, you will need to bleed the entire system

There is no way to install a bench bled master cylinder without introducing air into the system

It is black and white

We’re talking about somebody’s safety

A master cylinder can be bench bled and installed without bleeding the system. The pedal will be high and hard if done properly and no other defects are present.

You should be able to bleed the master cylinder with it installed in the car…It does not care if it’s clamped in a vice or installed in a car, the procedure is the same…The problem could just as easily be air trapped in the ABS , ABS failure, or a flex-line inflating and deflating as you pump the brakes…Back-yard methods of brake bleeding may not suffice…You many need to have the system pressure-bled with a machine made for that purpose…