Lock up

Tiny
JERRYBAK
  • MEMBER
  • 2005 HYUNDAI ELANTRA
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 75,000 MILES
After driving stop and go about ten minutes the front brakes will gradually stop releasing and the pedal gets very hard. Have to force the engine to go but the brakes will not release until I take off vacuum line off brake booster. I have replaced both front calipers, pads, rotors, front brake lines, master cylinder, and brake booster. Problem still occurs. The only parts I have not replaced are the metal brake lines, valves on master that brake lines go onto, and rear brakes. Anybody have an answer?
Tuesday, September 26th, 2017 AT 5:16 PM

3 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,762 POSTS
A constricted front rubber flex hose was a good suspect, but since those have been replaced already, look at the adjustment of the brake light switch to see if it is holding the brake pedal down a little.
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Thursday, February 25th, 2021 AT 11:11 AM
Tiny
JERRYBAK
  • MEMBER
  • 2 POSTS
I will check tomorrow. There has been no previous adjustment to this. Will this typically go out of adjustment? I will loosen it to allow less pressing down on plastic stop for light switch.
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Thursday, February 25th, 2021 AT 11:11 AM
Tiny
CARADIODOC
  • MECHANIC
  • 33,762 POSTS
You have already covered the typical stuff, so we have to look deeper. Besides the brake light switch, a lot of import cars use an adjustable push rod on the power brake booster. When locking brakes occur after replacing the booster or the master cylinder, that adjustment becomes a suspect.

We also have to consider brake fluid contaminated with a petroleum product like engine oil, transmission fluid, power steering fluid, or penetrating oil. Those will cause rubber parts to swell, and if any part with rubber in it is not replaced, the contamination will leach out of it and re-contaminate the new parts.

When this happens again, stop on a slight incline, shift to "neutral" place a block about a foot downhill of a tire, then loosen the steel lines at the master cylinder. If that does not make the brakes release, try opening the bleeder screws on the front calipers. The goal is to open the hydraulic system at various places to see where the brake fluid is being trapped.
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Thursday, February 25th, 2021 AT 11:11 AM

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