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3 master cylinders, 5 repairs in 2 months, and STILL too much play in brakes

I have 85,000 miles on my 2005 Hyundai Elantra GT, and started noticing (in November!) that my brakes were getting “loose”, i.e. more play before engaging. In March 2012, it got to the point that I took the car in for repair. Repair #1: mechanic replaced master cylinder with a rebuilt master cylinder. Worked for about 2 weeks, then loose brakes again. Repair #2: replaced master cylinder with rebuilt master cylinder #2. Worked for about 2 weeks, then loose brakes. Repair #3: replaced master cylinder with new master cylinder. Worked for about 2 weeks (seeing a pattern here?), then loose brakes. Repair #4: replaced hose to master cylinder. Worked for about 2 weeks, then loose brakes. Repair #5: tightened a connection to left front brake. Still have too much play - I have “0 braking to full braking” in about 25% of the distance that I did before (i.e. almost no braking until the pedal is near the floor). I don’t have to pump to get full braking, but there’s way too much play before I get ANY braking. HELP! I’m frustrated as $%&@, and know very little about cars! Thanks, all!

Does your car have rear drum brakes or discs? A quick look shows both are available.
Worn or out of adjustment rear brakes can mimic a failing master cylinder.

First, this may seem rather obvious, but when did you last have new brake pads and/or shoes installed on the front and rear? Worn pads and shoes can cause excessive pedal travel.

You’ve now replaced the master cylinder 3 times, right? If the master cylinder has failed 3 times in short succession, what explanation has your mechanic given? Master cylinders don’t fail three in a row. So your mechanic is either not very competent or doesn’t care to find the root problem.

I would suspect something in the antilock braking system, which has hydraulic components. If an ABS accumulator/actuator/valve isn’t working right, that could affect your normal braking.

First you need a mechanic who can actually diagnose the problem correctly. Click on the “Mechanics Files” tab on this website to find a recommended mechanic in your area. And don’t let anyone sell you another repair until he/she can explain exactly what the root problem is without blaming the master cylinder for no apparent reason.

By the way, the symptoms you describe could also be the result of air in the brake lines due to improper bleeding, and/or contaminated brake fluid, and/or brake fluid boiling due to heat generated by a stuck caliper.

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?

Have your mechanic check for a fifth bleed port in the rear brake lines. I have seen this in some vehicles where they put a bleed valve in the high point on the rear brake lines where air tends to accumulate. But based on your description, I really think the problem is in one of the ABS return lines.

It could also be a leak in the ABS module itself.

Thanks for your comments, everyone!

ok4550, I’ve got rear discs, but I don’t think that’s the problem (recently had pads and discs replaced, and car just inspected in February).

jesmed: I agree, problem is likely in the hydraulic system. Pads all checked recently and in good shape. Not a stuck caliper (I’ve had them before), and my mechanic is bleeding the system after each repair. (BTW, he wasn’t charging me for the repairs after the first, and was trying the easiest or most likely solutions first.)

gsragtop: Car does not pull when coming to a stop. Fluid level does not drop. No leaking detected. Suspect air is getting in, not fluid getting out.

First, a few thoughts.
I’m inclined to doubt if the ABS is a factor. The ABS system is simply a set of solenoid actuated valves, one in each brake line. When the ECU detects from the wheel speed sensors a wheel not turning, it sends a pulsed signal to the valve for that brake line. The pulsed signal flutters the valve, interfering with the hydraulic pressure. No mode of failure of the ABS system (short of a physical leak) has the ability to allow the pedal to sink.

Regarding the comment about air getting in without fluid getting out, that’s not possible. The fluid is subjected to far higher pressures when the pedal is pushed than the small amount of negative pressure created by any backdraw when the pedal is released. Any leak that would allow air in would squirt fluid out when the pedal is pressed.

One comment about bleeding: have any of the calipers been replaced? If an incorrect caliper was used and the bleed port is on the lower portion of the caliper rather than the upper portion, air will go into the upper portion of the caliper caliper and will be impossible to bleed out. Some calipers can fit on either side except that the location of the bleeder is different.

Air CAN get into a hydraulic brake system without leaking brake fluid. I’ve seen this on a few vehicles.

When the brakes are applied, the hydraulic pressure forces the caliper piston out along with causing the piston seal to expand. When the brakes are released and the piston is drawn slightly back into the caliper a slight amount of air can leak past the piston seal. Over time and depending how often the brakes are used, this air accumulates in one or both calipers and you end up with a soft brake pedal.

The last vehicle I replaced the calipers on for this problem was a 2003 Caravan.

Tester

In hindsight, Tester is right. Seals are designed to seal when under pressure in one direction, and can sometimes leak when reverse loaded, as the seals around the caliper pistons become when the pedal is released and the piston is pulled slightly back.

But I am still curious about the brake calipers.

Any luck Yet ?..Mike

COULD BE A MALFUNCYION IN THE POWER BREAK VACUUM BOOSTER OR THE PEDAL TRAVEL SENSOR. IF DEFECTIVE ENTIRE UNIT MUST BE PRPLACED. SOME CARS DO NOT HAVE A PEDAL TRAVEL SENSOR. CHECK FACTORY MANUAL… POWER BRAKES NEED TO BE BLED WITH THE PROPER POWER BLEEDER SYSTEM.
CHECH VACUUM CHECK VALVE TOO.
SOME MASTER CYLINDERS NEED TO BE BLED BEFORE INSTALLATION.
GOOD LUCK

Cub,

Please turn off the caps lock. It looks like SHOUTING!

Is the shop topping off the master cylinder so that the rubber boot under the cap is displacing fluid?

PARDON SIR
BUT I HAVE A HARD TIME READING THE LITTLE PRINT ON THIS NET BOOK AND ALSO PROBLEMS WITH SEEING THE KEYBOARD ONCE YOU GET OVER 75 MANY THINGS BECOME BECOME MORE DIFFICULT.
I APOLOGISE AND IF I GET ENOUGH COMMENTS ABOUT ALL CAPS I WILL NOT POST.
IF YOU READ MY PREVIOUS POST YOU WILL SEE THAT THERE ARE MISPELLINGS . CATARACT SURGERY WOULD CLEAR UP MY SHOUTING.
I TRY TO GIVE ACCURATE INFORMATION ON MY POSTS.

ctrl-shift-+ should enlarge the type. Can’t help with the keyboard.

Cubpilot, I empathize with your problem. I’ve worked teaching computers to senior citizens one of whom had difficulty seeing the text even when greatly enlarged. I urge you to please continue posting with us, even if you have to use all caps.

In this case I accept your caps as your way of compensatong with your disability. Normally we have a hard time with all caps, as they can be hard on the syes, but I would not want you to feel you can’t post just because you need to compensate for your vision difficulties. I welcome your input. I’m sure others here will agree.

I welcome your posts.