I just replaced the brake master cylinder in my 03 Santa Fe. The old one was causing the pedal to go slowly to the floor,,,5-6 seconds. I replaced it, after bench bleeding, and bleeding all the brakes. I'll be dammed if it's not doing the exact same thing! The pedal is hard when the engine is off. As soon as I start the engine, the pedal goes down almost to the floor. Could this be a booster problem, or a bad replacement cyl?

Thanx

 

I have personal experience with this issue. I had a 76 Mustang II that developed the same problem. After replacing the master cylinder and all slaves on the car, I was still getting no brake action. I finally removed and dismantled the vacuum booster. I discovered that a split had developed in one of the folds of the rubber diaphram that the vacuum pulls against to provide power assistance. I surmized the split was letting the vacuum pull against the back seal of the master cylinder with enough suck to drain it of fluid. My efforts to bleed the system were undone the moment I started the engine. Yes, I would remove and check out the booster.

 

Thanks for the reply ken99. But since I'm not loosing brake fluid, I don't think the problem you had with your Mustang is the same as mine, because you can feel the booster working when you start the engine.
I think the key difference is that I'm not loosing fluid. I'm going to re-bleed according to Hyundai's sequence, (RR,FL,RL,FR) and see if that makes any difference. But I really don't have much faith it will.

 

Nope,the bleeding did not help. I'm thinking I have another bad Master. Thoughts?

 

I gave up. Took it to my local mechanic. He bled it, took about 1/2 hr, it's fine. WTF?
I used a tube attached to the nipple with a check valve on the end of the tube. Never had a problem with this method in the past. Again WTF?

 

This is why people who are not trained, ASE certified mechanics should not work on important safety systems like the brakes. Next time take it to a trained mechanic first. You put yourself and the general driving public at risk.