Recently (last couple of days) I have noticed that when pressing on the brake pedal in my 99 Taurus, the pedal feel is normal for the first quarter of the movement, and then it suddenly gives out and drops another quarter and then feels a bit firmer. It doesn’t do it every time, but it seems to be getting more frequent. Does this sound like a brake booster?
No.
It sounds more like a brake master cylinder starting to leak internally.
Tester
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Got it, I can never keep it straight, what are the differences in symptoms between the two?
Yes.
When a booster fails, the brake pedal is rock hard while the engine is running.
When a brake master cylinder fails, hydraulic pressure is lost, and the brake pedal sinks slowly to the floor.
Tester
Got it, so if I try pressing the pedal when the engine is off, it should sink to the floor if it is my master cylinder, right? I’ll have to try that and see what happens.
Yes.
But first get the engine up to operating temperature before doing this test with the engine off.
Sometimes the under hood temperature can have an effect on the brake master cylinder function.
Tester
Got it, I’ll try it after my drive to work tomorrow and see what happens. The only thing throwing me off right now is after that drop I mentioned, the pedal is still at what I would consider a normal height, and it doesn’t seem to sink to the floor at all. Does that still sound consistent?
Not always that way, I forget which truck, an old smaller ford model, approaching a stop sigh no brakes until the last 1/4 of the pedal. (G I hope I spelled that correctly} so ended up blowing through a stop sign, limped it to the shop, do not recall what the exact problem was as it was a shop at work. Don’t take a chance, get it fixed!
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So I just did the test, and the pedal is solid. I tried bearing down as hard as I could on it, and there’s no give.