Brakes are locking up why?

Tiny
YOURMINKY
  • MEMBER
  • 2000 HYUNDAI ELANTRA
  • 2.0L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 105,000 MILES
No ABS. The brakes are locking up intermittently in stop and go traffic for the last few months.
When the wheel/brake lock up, the brake pedal is stuck at the up position, brake becomes super sensitive, the car drags and just touching the brake stops the car. Pressing with a lot of force will not make the brake pedal go down, it stays stuck at up position for ten minutes even with the engine off. Then fifteen minutes after turning the engine off, the brake pedal would go down a little bit. After thirty minutes the brake pedal goes down and up normally, the car drives normally afterwards for the rest of the day. After this locking issue started happening, over the last few months I have put in the following:
New brake pads and shoes on all four with new hardware.
New rubber flex brake hoses for both front brakes.
New wheel cylinders in both back brakes.
New caliper with piston assembly in front driver side. Passenger side is fine.
New wheel bearing in front driver side. Other bearings are fine.
New tires on all 4four.
Flushed brake fluid, fluid look clean and not contaminated.

None of the above fixed the problem. Any ideas?
Friday, December 8th, 2017 AT 10:32 PM

14 Replies

Tiny
STEVE W.
  • MECHANIC
  • 12,950 POSTS
My guess would be an issue with the brake booster diaphragm. About the only test I can think of would be to pull the booster vacuum line and check valve off when this happens and see if it reverts back to "normal". The only other item would be a build up of brake pressure in the lines to the master cylinder from heat, but unless you routed the brake lines next to the engine or exhaust I do not see that being the issue.
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Friday, December 8th, 2017 AT 11:43 PM
Tiny
YOURMINKY
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Can you please explain how the defective brake booster diaphragm can cause the brake pedal to be so stiff and be stuck in up position for ten to fifteen minutes?
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Saturday, December 9th, 2017 AT 12:36 AM
Tiny
YOURMINKY
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It is no longer an intermittent issue, the brakes lock every time after a few miles. I touched the front driver side lug nuts and they were sizzling hot. Front passenger side was not as hot. Back nuts temp were normal. I also noticed the brake gets so sensitive that the car stops before the brake travels far enough to activate the brake light switch. Can the pedal automatically lose adjustment after seventeen years of use? How about a warped rotor on front driver side, can it cause such locking?
I still have the original master cylinder and pedal and no one adjusted those ever. My vacuum booster also has a proportioning valve attached to it. Do I have to move the proportioning valve in order to remove the master cylinder to check the push-rod clearance (see photo)?
I tested the vacuum by pressing the brake pedal several times with the engine off and then holding the pedal down. Then I turned the engine on. The pedal goes down fine when the engine starts and creates the vacuum.
My vacuum check valve is not removable (photo).
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Monday, December 11th, 2017 AT 8:22 PM
Tiny
STEVE W.
  • MECHANIC
  • 12,950 POSTS
You replaced that caliper, did you also go over the slides and make sure there is no binding. The brakes getting hot will cause the fluid to expand but I've never seen one that also made the pedal act up the way yours is. That is because of the bleed ports in the master cylinder, when you apply the brakes the pistons move and block those ports. When the pedal moves back up the ports are open and any fluid expansion should just push into the reservoir. Then there is the prop valve. It could be faulty and cause the brake to rub and heat up, but the way it's designed if it is holding the pressure the master cylinder shouldn't be effected either.

That's why I suggested the booster, if it is applying the brakes just enough that they start to heat up it could cause both problems. I would try disconnecting the booster, then see if the condition is still there. Next would be to drive it and once it locks up, use a wrench and loosen the lines at the master cylinder. They shouldn't have pressure there. If either or both has pressure in them then move to the proportioning valve.

One way to discover if the heating LH brake is causing the problem or if it's the result would be to remove the banjo bolt and replace it with a solid bolt the same size and see if the problem is still there. Just be prepared for the odd handling of only one front brake during the testing.
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Friday, December 15th, 2017 AT 1:14 PM
Tiny
YOURMINKY
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  • 106 POSTS
It is a re-manufactured caliper assembly. I added silicon syl-glide lubricant to the sliding pins and checked them last week and they were sliding fine.
You suggested that I unscrew the brake line when the brakes lock to see if that releases the lock. To test this, do I unscrew the brake line at the MC or at the proportioning valve? Will it have the same effect if I open the bleeding screw at one of the front wheels? You mentioned there shouldn't be any pressure. Does it mean no brake fluid should drip out when I start unscrewing the brake line? Will it have the same effect if I unscrew the bleeding screw at the brake?
I haven't driven the car lately but I was able to use PB-blaster and safely unscrew the MC mounting bolt from the booster. The proportioning valve was attached to the bracket, so it moved as well. Some of suggested it could be a pushrod or pedal issue. I'll drive the car today or tomorrow and if it locks, I'll unbolt the MC and give it about 1/4 (quarter) inch slack for a minute and then bolt it back and report back to you guys.
BTW, I flushed the brake fluid and bled all four brakes yesterday. Existing fluid color was fine, not dark or rusty.
I'll keep you posted.
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Sunday, December 17th, 2017 AT 12:15 PM
Tiny
STEVE W.
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If the calipers are OK the issue almost has to be in the proportioning valve. The pressure increase is causing the valve to block brake pressure to the rear brake, if it wasn't the rear would be hot from rubbing as well.
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Sunday, December 17th, 2017 AT 2:37 PM
Tiny
YOURMINKY
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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 AGAIN the day before yesterday and rotated all 4 tires, loosened and finger 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 today but the wheel/brake wont lock again, the car is running fine for now. Note that before latest flushing, the brakes were locking everyday after driving for 5 miles or so.
I'll update when the brake locks up again.
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Monday, December 18th, 2017 AT 9:35 PM
Tiny
STEVE W.
  • MECHANIC
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Mixed fluid could cause issues but I don't think it would cause locking up. My thought is that maybe this last flush moved something in the valving and freed it up. Hard to really tell as the "normal" items seem to be missing from the puzzle. 5 miles would even be a trick for sticking calipers unless the were so tight the car would barely move with no brake applied.
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Tuesday, December 19th, 2017 AT 1:37 PM
Tiny
YOURMINKY
  • MEMBER
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Yes, when the brakes locked previously, the car wont move unless I gave it some gas. Normally, just lifting the foot off the brake pedal puts the car in motion.
I drove the car around for 30 miles today, city traffic. Drove on the Interstate @ 70+ MPH for a short while. The brakes have not locked since the last flush 2 days ago. The 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 sizzling hot like before, just warm.
Will update again soon.
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Tuesday, December 19th, 2017 AT 7:39 PM
Tiny
STEVE W.
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Please keep us informed.
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Tuesday, December 19th, 2017 AT 7:58 PM
Tiny
YOURMINKY
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I did not drive the car today.
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Wednesday, December 20th, 2017 AT 9:02 PM
Tiny
STEVE W.
  • MECHANIC
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No problem. Drive it around when you can, if it never acts up again, great, if it does then we'll keep digging until we find the problem and fix it. Good Luck.
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Thursday, December 21st, 2017 AT 5:58 AM
Tiny
COMPUCARL
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  • 4 POSTS
I my self am having the exact same issue i believe. see post (https://www.2carpros.com/questions/brakes-lock-til-systems-shut-off/r/2572370) do you have any codes? and does it start working after both the brake and ABS lights come on. mine always happens when i first get into the car and have to ride them to get the lights to come on.sorry i am no help but kinda glad someone else has the same issue - Compucarl _
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Thursday, November 7th, 2019 AT 10:58 PM
Tiny
STEVE W.
  • MECHANIC
  • 12,950 POSTS
COMPUCARL Could you please post this as a new question. Give all the vehicle information you can including anything that was done to the brakes and any testing. Thank you.
https://www.2carpros.com/questions/new
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Saturday, November 9th, 2019 AT 2:38 AM

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