Spongy brake pedal 2005 Hyundai Santa Fe

[B@ssmaster]

My wife's 2005 Hyundai Santa Fe, V6 3.5L, with 38k miles, has had an issue with the brakes for almost a year now. Need some troubleshooting ideas. The local dealer had it for over a week this past summer and couldn't get it figured out (permanently), another local shop failed as well.

The pedal goes nearly to the floor every time you push it for the first time. You can pump the pedal it up, briefly, but then it fairly quickly goes to the floor again if you continue to hold the pedal - as in sitting at the stop sign. Does not act soft at all when the engine is not running. There is NO pedal fade when the engine is off and I press the pedal hard. No fluid loss that I can detect, either by sight or finding low levels in the reservoir. I've had all 4 wheels off and inspected, checked rigid and flexible lines, etc. I haven’t personally checked to see if there is any fluid blowby on the master cylinder shaft leaking into the vacuum assist unit, but I have made the assumption that since there is no detectable fluid loss in the reservoir that there is no seal problem on the master cylinder. (Could be an incorrect assumption though, but given that there have been TWO new masters installed, I am guessing a leak on 3 different masters is unlikely.)

Over the various repair attempts, the truck has had new front calipers, two new master cylinders, two (used) vacuum assist units. (For each part replacement I was assured that the “bad” part was verified bad and that the replacement part WILL fix the problem.)

To be fair, the last vacuum assist unit fixed the problem for about 2 months, then the problem returned.

I’m done taking it to these two shops that apparently can’t troubleshoot, they only replace parts randomly. I have to find an expert, (or become one - .)

And just to complicate matters, the dealer has informed me that the bleeding process for this vehicle (for a couple of model years) is an extreme pain in the butt, so it takes a long time to be sure that all air has been evacuated (something to do with a computer needing to be connected to the vehicle and cycle the ABS valve, the angle of the valve body is such that it is not conducive to the air bubbles flowing out – they get trapped, etc.) One early theory was that they were not getting all the air out of the system (after various parts were replaced) but they spent the better part of a day bleeding the system to ensure it was purged. I don’t have the proper equipment to bleed the system, so if I crack it open, I have to get it someplace that can do that part for me…..

Any ideas on what to check next?

(The only think I can think of is that the used vacuum assist unit failed. The dealer wanted $900 for a new one –ouch!, thus the used part. I’ve found out since that the local part shop can get one far cheaper, but I am not sure that is the issue yet, don’t want to be guessing like the two shops apparently have been doing...)

[1968]

Your pedal drop sounds like the classic symptom of an internally bypassing master cylinder. This can happen without external leakage.

While rare, ABS units can "bypass" as well. Temporary plumbing may need to be fabricated to take the ABS out of the picture if all else is inconclusive. Basically plug/bypass/bleed components until the pedal is right. Sounds like a toughie for sure, as long as everything up to this point has been done correctly.

Maybe a fresh pair of hands is what the doctor ordered. With a ridiculous manufacturers warranty that the tech's are basically forced to subsidize, quality/caring help may be lacking at your car's dealer.

[Jeremy airjer W]

Rear disc or drum brakes?

[B@ssmaster]

It has rear disc.