My brakes are sticking

When you press the brake pedal and then release it, the pedal should immediately release and release pressure from the master cylinder which means the calipers will "spring" back and push the fluid back to the reservoir. If the calipers are not releasing then it is normally a caliper but if you have both front calipers doing it then more than likely it is something they have in common. So if they slowly release then that is because the fluid is being restricted from returning. This happens when the brake booster push rod is adjusted out too far which does no allow the brake master to return fully holding the brakes on . To confirm the issue loosen the brake master mounting bolts 3 turns to see if the car starts to roll again, if so remove the master and adjust the booster push rod inward.

First, press the brake pedal and watch to see if it is releasing or returning to the proper position or is it remaining low.

Unless the pedal is getting stuck on something (unlikely) then the most likely cause is the brake booster. Basically there is to be vacuum on both sides of the diaphragm but the air valve between the two sides sticks and holds pressure which doesn't allow the spring in the diaphragm to return the pedal to return. This holds the fluid in the calipers and doesn't allow the brakes to release.

Have you checked the rear brakes to see if they are holding as well? If it is just the front then the master cylinder is most likely the issue.

Let me know what you find and we can go from there. Thanks

Thank you for the feedback. The pedal returns to the top position without issue.

Just drove the car this morning and it was fine for the first 30 minutes/20 miles of start stop driving. Now the car stays in position when I release brakes at stop signs. Just jacked rear wheel and it is also hanging up.

It is odd to me that it took a some drive time for the issue to resurface but this is consistent with performance after I replaced the front brakes, calipers and rotors 3 days ago.

I really appreciate your insight while working through this issue. Thank you!!

Hi guys. Please let me add a few comments of value, then I'll go sit in my corner.

If someone added brake fluid in between, it is going to run over and make a huge mess. That brake fluid eats paint too. If there is no obvious leak, low brake fluid level is an indication a brake system inspection is in order as part of regular maintenance, and expect to find the front disc brake pads need to be replaced.. I'm sure some of these owners will share their complaint with anyone who will listen, and some of them will top off their own brake fluid. You have to wonder how many of them will unwittingly contaminate their brake systems, and if a problem develops, it is likely to become one of those "ever since" issues. "Ever since" that shop worked on my car, it has had this problem. The best we can do to prevent this is education.

CARADIODOC I truly appreciate the thoroughness of your response. Your feedback is that of what one may refer to as a subject matter expert.

The simplicity of the potential issue being related to the oxidation of the flexible line clamps is flooring to say the least.

Regarding the potential of petroleum contamination, I have a much better appreciation for the various ways contamination can occur. Thank you for the education!!

The latest diagnosis provided by my mainstream repair facility of choice is the master cylinder. I will share my newly gained knowledge with them and with fingers crossed, we will resolve the issue.

Respectfully,

mklosek

Sounds great. Let us know. Thanks

The issue has raised its ugly head again following the replacement of the master cylinder. It has taken nearly a month to realize the master cylinder was not the issue due to limited use of the vehicle due to the pandemic lock-down.

After start stop driving for 30 minutes or so the brakes began to drag resulting in steering wheel shimmy, excessively hot “front” lug nuts, 3,000 rpm’s to accelerate to 40 mph and that awful burning brake pad smell.

Thoughts?

We need to find out which wheels are doing it. I would suggest driving the vehicle to where it is acting up and then lift the vehicle and spin the wheels to see which one is grabbing. At that point we can test that leg of the system.

Let me know what questions you have and we can figure it out. Thanks

Thank you for the reply KaseKenny1. I have dropped the vehicle off at my repair shop so cannot further diagnose. On the two previous occasions, the lockup appeared to be isolated to both front wheels as the rear wheels did spin free and the rear lug nuts were not hot like the front.

Okay. That could be an issue with the proportioning valve. Basically this determines how much pressure to send to the front and rear brakes. It tries to keep the front or rear from locking up but it may be sending too much pressure to the front causing them to drag.

Keep us posted on what they find. Thanks.

Good news folks!! The issue has been resolved with the replacement of the flexible front brake lines. I truly appreciate all of the support CARADIODOC and KASEKENNY1.

Dandy. Happy to hear you solved it.

only happens sometimes, but if i come to a complete stop and release the pedal the brakes lock then slowly release. any idea what is wrong? also, the ESC light came on but eventually went off.

Can you tell if it's front or rear OR all 4?

As the ESC light came on it should have stored a code but you need a factory grade scan tool to read them, the free scans only cover the engine codes. If you can get the codes it would make it easier. Without them the below are the likely culprits.

The description sounds like you have a sticking caliper piston. That could be due to uneven pad wear that twists the caliper. Checking requires removal of the wheel/tire and visual inspection of the pads and rotors to see if they are worn uneven.

It could also be a failing flexible brake line. They can fail inside and act like a one way valve. You apply the brakes and the fluid either cannot return or returns very slowly.
These can be hard to find if it only happens once in a while because they will look fine on the outside. Sometimes you can find them if you jack up the vehicle and stomp the brake and have someone immediately try to spin the wheel by hand as soon as your foot is off the pedal. If the wheel is hard to turn and slowly gets easier I would suspect the line.

If it's all 4 I would look at the master cylinder and the ABS module, after getting the codes.

put new breaks and master cylinder in no leaks

Brake fluid is trapped and can't get back to the master cylinder. When it happens again, loosen the mounting bolts for the master cylinder. If the brakes release, check the push rod to see if it's over-adjusted, or if the brake light switch is misadjusted and holding the brake pedal down. If they don't release, open the bleeder screws at the front calipers. If the brakes release there, check the rubber flex hoses.

Why did you replace the master cylinder? Any chance the fluid is contaminated with petroleum product?

this happened 3 months ago and the mechanic put master cylinder in it was fine for 3 months nows it started again this week

The first thing to check is the rubber bladder seal under the reservoir cap. If it's blown up and mushy, there' a petroleum-based contaminant in the brake fluid. The only proper repair for that is to replace every part in the hydraulic system that contains rubber parts that contacts the brake fluid, and all steel lines must be flushed and dried.

At 52,000 miles and six years old, it's very unlikely the master cylinder failed on its own. If it failed due to fluid contamination, that contamination will leach back out of other seals and hoses and recontaminate the new master cylinder. That typically takes a few weeks to a couple of months.

The way to prove or disprove this is to loosen the steel lines right at the master cylinder while the brakes are locked up. If they release, fluid contamination is the chief suspect. The misadjusted push rod or brake light switch that I mentioned previously wouldn't be okay for three months, then suddenly start causing a problem.

I have an 6/04 hyundai sonata and have replaced the rear pads rear rotors, rear calipers front and rear brk hoses, fluid, and while driving the front and rear brks start locking up

Please be more specific, does it feel like ABS braking or a complete brake lock-up, such as all four wheels locking up and staying applied and not releasing. Does the ABS light flash when this happens? Did you have any problems of note when changing the brakes? Did everything install back into place with no problems?

All four complete brake lock-up and does not release until resting for approx. 1 hour. and yes the abs light is on

Is it possible that any of the old brakes pads were ground down to metal before replacement? Some metal shavings may have magnetically stuck to abs wheel sensors. I would try to remove the shavings and clean the wheel speed sensors, check all wiring to and from these wheel speed sensors. If all checks out, a code check of the ABS module will need to be doe with a scanner. You may remove the abs pump motor fuses. Not recommended, but may isolate problem, if it still occurs with abs motor having no power, it is your basic hydraulic system. I personally feel you have a ABS issue.

I’ve replaced everything in the braking system. when I take off the brake line and it returns to normal again. What should I try next?

Hi,

Did you replace the rubber brake hoses at the brake calipers? Also, do all the brakes lock up or just one?

Let me know what has been replaced and exactly what is happening.

Take care,
Joe

And master cylinder was replaced front brakes lock up only.
Brakes lock up even if car is not moving when we unplug the brake line from engine brakes loosen again and when they lock up and your driving it overheated the car.

Okay, so it locks up when you apply vacuum to the brake booster, correct? If you disconnect the booster and it releases, it sounds like the booster itself is bad.

When the car first came to you, what was the problem?

Joe

I replaced the filter.
When I got the car I drove it for a few months and then it started locking up when driving later we took it to a mechanic we let it warm up they locked up sitting not moving.

What filter was replaced? Also, is it a vacuum supply you are referring to?

Joe

Not filter brake booster.
When you unplug the brake tube vacuum.

If they only lock when the brake booster is connected to vacuum, it sounds like the booster is bad. I realize you replaced it and it worked for some time, but it sounds bad.

Joe

I have a 2002 Hyundai sonata 2.4 no abs. I drive about 5 miles and brakes lock up. I disconnect hose from booster and it release brakes. I replaced booster with a used one and it did the same thing. I inspect master cylinder and no fluid leak at master be I replaced power brake booster

When this happens, do all brakes lock up or just start to drag? Have you reciently replaced the master cylinder? Have you examined the booster check valve?

How much pressure should the vacuum have?

I have a Sonata 2005 2.7(V6)GLS NO ABS NO Traction Control drive about 4-8 miles depending on the temp. cooler it takes a little longer, the front brakes lock up till you cannot move. Have redone the whole braking system new everthing !!! This car only has 61,521 miles has been maintained well never experience anything else, no noises or anything. Replaced front pads last year. This started out of the blue while driving home, no indication of anything till all of a sudden. Frustrated, and confused cause noone seems to know what the problem is, I have replaced several parts from auto store to another. My car seems to use '04 parts and '05 parts.......Have not taken to dealer as of yet, have a personal mechanic by trade that does everything for this car and he cannot figure this one out. HELP! HELP!

Hi,

The vacuum is right from the intake. Most internal combustion engine's hold between 15 and 18 inches of vacuum when idling. The will drop when the engine is under a load or when the throttle is pressed.

Joe

What happens is the internal valve inside the booster gets stuck so it wont release. The booster needs to the replaced or the booster rod is adjusted too far out. Try to undo the mounting bolts for the master to see if that releases it as well if so then turn the rod adjustment screw inward. If not here are some diagrams to help you replace the booster with a rebuilt or new unit.

Please let us know what happens.

Cheers, Ken

repaired a wheel cylinder on back, now the front brakes lock up about every five miles. this car does not have ABS and do not see a release valve. i can release the pressure at the bleeder or the master.
got a new master same thing still happening.

i also backed the screws out on the master cylinder to see if the rod was keeping it in. still locked up. maybe i did not unscrew it enough?

Check the brake pedal adjustment. If there is insufficient free play, the master cylinder would be partially depressed and this would result in the brakes seizing after the brake fluid heats up. Insufficient free play could be due to a mis-adjusted brake switch.

i figured it out it is the brake booster not sure if the pedal is adjustable or not. However, the screw is just have to take the master all the way off to adjust it.

Before adjusting the brake booster, check the brake pedal free play adjustment first. It is adjustable, either by the push rod or the brake switch if the pedal is low.