Help diagnose intermittent brake locking dragging issue

2000 model. The brakes are locking up intermittently in stop and go traffic for the last few months. I removed the front tires. The brake pads were locked solid and the rotor wont rotate at all. Brake and wheel were blistering hot. Front driver side was hotter than front passenger side. Note that brake master cylinder and reservoir are closest to the front driver side. When the wheel/brake lock up, the brake pedal is stuck at the up position. Pressing with all my might wont make the brake pedal go down. The car drags and struggles to move forward or backward when it happens.
15 minutes after turning the engine off, the brake pedal would go down a little bit. After 30 minutes everything becomes normal, the brake pedal goes down and up normally, the car drives normally afterwards for the rest of the day.
The car also runs louder than before. Rotating the steering wheel to the right diminishes the road noise partially.
People gave me a whole list of things that could be causing this. After this locking issue started happening, over the last few months I replaced the following parts:

  1. New brake pads and shoes on all 4 with new hardware.
  2. New rubber brake hoses in both front brakes.
  3. New wheel cylinders in both back brakes.
  4. New caliper with piston assembly in front driver side. Passenger side is fine.
  5. New wheel bearing in front driver side (there was visible smoke from front driver wheel when it first happened). Other bearings are fine.
  6. New cheap Chinese tires on all 4.
  7. Bled a large bottle of new brake fluid through the system.

None of the above fixed the problem and I am running out of $$ and ideas. Any ideas what may me be causing this intermittent brake locking issue?

vacuum brake booster engaging when it is not supposed to?

Good idea to let us know the make and model. My first guess was the rubber brake hoses, but you’ve replace those already … which was a good start, but apparently didn’t do the trick … hmmm … well, if I had that problem and a visual inspection didn’t discover the problem and I’d already done what you’ve done, and the booster tested ok, and there were no ABS codes, no CEL, next thing I’d do, I’d replace the master cylinder and both of the front calipers and all the brake fluid.

2000 model what?

Honda? Chevy?

Try walking into a parts store and ask for brake parts for a 2000 model and see how far you get.


I am not sure. How can I diagnose if it is engaging or not?

When I posted, it asked for my car make and model. I thought that would propagate to the posting. It did not. 2000 Hyundai Elnatra. No ABS.
Thanks George_San_Jose1. I already replaced the front-driver side caliper assembly. The other one looks and works OK. So, you are saying it could be the master cylinder?

Yes, that’s a definite suspect. Take a look at the brake pedal area under the dashboard too, to make sure no broken parts, everything move freely etc down there. Test the brake booster to make sure it hold vacuum at least. You’re not losing brake fluid, right? And no black smoke coming out the tailpipe, right?

I will Google how to test a bad master cylinder and also how to test the brake booster to check if it holds vacuum.
I’m not losing brake fluid. No black smoke. No broken parts under the pedal or dashboard.

Sorry about that. When I posted, it asked for my car make and model. I thought that would propagate to the posting. It did not. 2000 Hyundai Elnatra. No ABS.

Would a bad master cylinder cause intermittent locking issues? Can you explain how?

I’ve never had a bad MC cause the brakes to lock to my cars. But I’ve never had a locking brakes problem either. Posters here have said a bad MC can cause the brakes to lock though. And I believe posters here have said they fixed locking brakes by replacing the MC.

What’s the mechanism? Take a look at the figure titled “diagram of a MC” in the link below. As the brake pedal is pushed (right to left in the diagram) the pistons do two things: (1) close off the path to the reservoir above, and (2) force fluid into the brake lines under pressure. When the pedal is released the pistons should move right to left, and allow the pressurized brake fluid in the lines to move back into the reservoir above through the 4 ports shown(2 per piston). If the piston were to get stuck in the bore, or if those 4 ports (which are very tiny and could easily clog in an actual MC) were not allowing fluid to pass freely, conceivably that could cause the brake lines to remain partially pressurized after you let your foot off the brake. Which would lock the brakes.

I’ve been throwing parts at it based on people’s guesses. I’m not convinced it is the master cylinder based on the info provided by the forum experts.
I want to focus on the push-rod at the vacuum booster. Can it get extended one millimeter after 17 years of use? How about on the brake pedal side? What are the factory specs for this care so I can test?

It is no longer an intermittent issue. The brakes lock after a few miles of driving, every time. I also noticed the brake gets so sensitive that the car stops before the brake travels far enough to activate the brake light switch.

I flushed the brake fluid and bled all four brakes yesterday. I’ll keep you posted.

I flushed the brake fluid in April of 2017, used Prestone synthetic DOT3 brake fluid $8.99 each bottle. This synthetic brake fluid won’t mix well with existing DOT3 fluid, it would create a separate layer when poured and then slowly mix, shining bright light will show separate blobs of liquid. Maybe that caused the brake locking issue.
I flushed the whole brake system day before yesterday and rotated all 4 tires, loosened and hand tightened the master cylinder mounting bolts. I used Super Tech (Walmart) DOT3 brake fluid $1.89 a bottle this time. I drove around all day but the wheel/brake wont lock again, the car is running fine for now. I’ll update when the brake locks up again.

Good observation. I’m not sure what the restrictions are when mixing different type of brake fluids. I’ve always used dot 3 exclusively, so haven’t had to deal with that issue.

I drove the car around for ~30 miles today, city traffic. Drove on the Interstate @ 70+ MPH for a short while. The brakes did not lock, even though road/engine noise has been louder ever since early summer of this year when this issue started. I took temperatures of all wheels several times. Today and yesterday the front driver side lug nuts got warmer than the front passenger side - just opposite of the past experience - however, they were NOT HOT.
Will update again soon.

Did this fix your problem ? I’m having about the same issue at the moment of a family members car.

It was bad brake fluid. I flushed the fluid and all is OK for a long time now.