I have a 2005 Hyundai Santa Fe that keeps getting air in the brake system. Have been to four different places and they have replaced the master cylinder, new brake pads, replaced the right front brake line and caliper and have bled the brake lines numerous times. I get full pressure for 2-5 days and then the spongy brake returns with air in the front right. It is not leaking break fluid and all systems that they think could let in air seem to be working properly.
I can only think of two possibilities; the ABS/stability control modulator or the seal between the booster and the master cylinder. Either should also pass fluid. With the modulator, there should be drip marks on the outside case. With the booster, fluid might be running into the diaphragm canister, or perhaps even the driver floor, depending on exactly how the booster is configured.
NOTE: these are Wild A Guesses. But they’re the only spots I can think of that have the potential to allow air to be drawn in that you haven’t changed.
My wag the bleeder screw, maybe it is the failing component, as everything else has been done
Sometimes there are nooks and crannies where the air hides. As you step on the brake pedal, it forces the air out towards the ends of the lines. It seems like if you keep bleeding the right front once a day for a while (assuming you are driving the car daily), eventually you’ll have to get all the air out. Either that or there is a faulty component (e.g. the bleeder screw mentioned by @Barkydog) that is allowing air to leak in. I tend to doubt this however, as if air can leak in, fluid can usually leak out, and you’d see it drippingon the ground and notice a loss of fluid in the master cylinder.
The only other thing I can think of is that the proper bleeding procedure isn’t being followed. This varies from car to car, by make and model. The manufacturer’s shop manual for your car will have this specific information for you car. For example, when installing a master cylinder, they usually recommend that it be bench bled (where it can be aligned to be perfectly horizontal) before installing it on the car.
Along with Barky’s idea, are you sure you’re bleeding it correctly? Is the bleeder tightened properly? Maybe it isn’t seated right? Are you using the correct bleeding sequence#?
Are you also bleeding into a jar with the hose being dipped under some brake fluid so air can’t come back right before you close the bleeder?
(Passenger Rear, Driver Front, Driver Rear, Passenger Front for a lot of cars - check Hyundai’s manual to be sure)
I think the problem is still with the right caliper even thou it was replaced. Everything from the master cylinder, the hose to the caliper, and the caliper were replaced. If it were a problem with the master cylinder there would be air in all the brakes. If there were a problem with the hose to the caliper it would leak brake fluid. However, if the replacement right caliper allows air into the system past the caliper piston seal each time the brakes are released, this air accumulates in the right caliper depending how often the brakes are applied and released.
Have a NEW not a rebuilt right caliper installed.
Tester
A few weeks ago another poster, who had a similar car, was also having issues with his brakes bleeding down. In his case air had gotten into the ABS modual and he could not get it blead. It turns out there is a special bleeding proceedure for your car, that only the dealer can do. It involves tuning on the ABS pump while bleeding to get the air out of it. Maybe this is your issue??
gsragtop: you as asked this question on another posting back in June about a similar issue with brakes:" I also think you have a bleeding issue, where they are bleeding the lines after every repair… So the brakes feel fine for a few weeks… Durring that time you must be sucking air in from somewhere, and that is causing the brakes to get weak again… Does you car pull in any direction when coming to a stop? Has the brakes been checked for leaks? Does the fluid level drop durring those two weeks? "
In my case the veh does pull to the left when I stop. Like the left brake is grabbing and the right one isn’t so much.
HMM, if that is the case it points to @testers point. If the caliper on the right was bad, the car would pull left when you hit the brakes. Does it do this all the time, or just after the brakes get soft again?
Just after the brakes go soft again.
I just thought of something: the bleeder valve on that new right front cylinder, is it on the top or the bottom of the caliper? I’ve heard of a caliper being put on the wrong side of the car (or wrong caliper used) and if the bleeder is on the bottom of the caliper rather than the top the caliper cannot be properly bled.
Are you loosing any brake fluid at all. You may think it is not leaking, and it may be difficult to tell, but I suspect that if you went to one mechanic exclusively, you might find out that you are leaking brake fluid somewhere. When you jump from one place to another, each new mechanic does not know where the brake fluid level was at the last time.
Master Cyl prolly :_)