Brake pedal goes half-way to the floor, only the first time

Brake pedal goes half-way to the floor, only the first time.

Finally driving my car again after it was laid up for 2 months.

I don't think it was like this 3 months ago.

When I first press the brake pedal, it goes half-way, but certainly not all the way, to the floor, and at t hat point it stops the car very well. If I press the pedal again within 2 or 3 minutes, it moves very little before it's stopping the car.

If I wait maybe 15?? minutes, it's like the first sentence in the previous paragraph.

What's the problem?

Bad master cylinder?

If you disconnected the caliper while you were working on the front end the system probably needs bleeding - even if you didn't it probably does . Some cars require bleeding both front and rear systems to maintain balance in the valving system . Your repair manual should have the procedure .

No, I didn't. (For others planning to do this: At first I did what I usually do, I hung the caliper from other parts using a bent wire hanger, but later I had a loop of fairly heavy stranded electrical wire and that worked better.)

Is the symptom I have really caused by needing bleeding? I had spongy brakes once after doing something to the brakes, and every time I pushed the pedal it was the same, spongy, like stepping on a sponge. Now it's never spongy. When the pedal is going down the first time, there is almost no resistance (only what comes from the spring) until there is normal resistance.

I'm foggy, but I think it could be a brake opening up mechanically, more than normal, as you drive, gradually pushing fluid back into the master cylinder.

If you have drums in the rear, one or both may need adjustment. Sometimes pulling up the slack with the parking brake will act as a temporary adjustment. If a rotor is warped, it could move the caliper back and forth as you drive, gradually opening it.

micky posted for all of us...

Is this the same car you did the suspension work on? If so you may have introduced air into the system through cracks in the hose or bulging. The first step is to top off the master cylinder then bleed the brakes properly, per manufacturers instructions. If that doesn't work it is probably the master cylinder, diagnose and repair per manufacturers instructions. If it has power brakes it may be the booster but IDK your set up. I have a faulty memory on this subject.

that is indeed, the text-book symptom of a bad master cylinder.

GW

Given the recent history of the vehicle -IE- it's damage history, I'd be looking at the brake on the damaged axle first. Clamp off the brake flex hose to that wheel. Is the pedal highand firm? If not, look elsewhere. If so, you know where to look. Brake hose clamps are available at Harbor frioeght and many auto parts/tool suppliers at reasonable cost. Some are little screw clamps, others are a vice-grips with round rod jaws. Make your own by brazing a 1/4 inch long 1/4 or