When hot outside all four brakes lock on

Tiny
DWM1321
  • MEMBER
  • 2011 BUICK REGAL
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 143,000 MILES
When I leave work from my car sitting in a hot paved parking lot during the day over approx 90 degrees outside according to my car temperature, all 4 of my brakes are locked on. When I put brake on to take it out of gear they do not release. I drive it down the road for about a mile with steering wheel starting to shake and gas pedal to the floor to a shade tree to cool down. All 4 wheels are very hot to touch and smell of burning brakes. After 5 to 10 minutes of cool down in shade I am good to go. Last year this only happened 3 times when it got to a 100 degrees outside. This year much more often at a lower temperature. The dealer and other shops say they never heard of this. I was thinking bad brake rubber hoses but I don't think so and all 4 at the same time? This has me and everyone stumped. Once summer hot weather passes it will work fine.
Sunday, July 28th, 2019 AT 9:54 AM

4 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,959 POSTS
Welcome to 2CarPros. This wouldn't be the hoses, it would more than likely be the master cylinder not venting properly or there is an issue in the ABS module.
When the car is setting still the master cylinder piston assembly should set at a point when the front lip of the seals are clear of the fluid ports and as the fluid heats up it can expand through the system and the "extra" fluid simply goes into the reservoir. The reservoir is supposed to have a diaphragm inside the cover that moves with the fluid and above it is vented to the air. Your description sounds like either the vent is blocked and not allowing the fluid to equalize or the pistons are in the wrong spot and that is blocking those return ports. When you get in and step on the brake is it hard to push down when the brakes are locked? Or does it move and feel like it does all the rest of the time?

When was the last time the brake fluid was flushed with new fluid? That would be the first thing I would do as contaminated fluid can heat up and expand more than new. I would also make sure the reservoir vent and diaphragm in the cap are OK. When the system is flushed make sure to use a scan tool to activate the ABS module to purge it as well.

Those are about the only parts that will cause all 4 brakes to lock on as the system on that car is split so the front and rear fluid paths are divided everywhere else after the master cylinder.
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Sunday, July 28th, 2019 AT 10:35 AM
Tiny
DWM1321
  • MEMBER
  • 3 POSTS
Thanks I will try that. Someone just mentioned that to me today about contaminated fluid. The diaphragm is good I will check cap. I know overfull reservoir could also cause it but it isn't. As far as I know the fluid had never been flushed so I will try that next. Is it also possible when I got someone else to do the oil change that they topped off the brake fluid with maybe power steering fluid, an incompatible brake fluid, or some other fluid other than brake fluid by mistake?
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Sunday, July 28th, 2019 AT 11:33 AM
Tiny
DWM1321
  • MEMBER
  • 3 POSTS
I missed your other question. Yes, the brake pedal feels the same as normal whether the brakes are locked on our not.
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Sunday, July 28th, 2019 AT 11:39 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,959 POSTS
If they ever put the wrong fluid in you would have found that about the third time you stepped on the brakes. Any type of oil will literally melt the brake parts that are made of "rubber" like the piston cups in the master cylinder and the rubber lines will become soft and gooey. However brake fluid sucks up water and then you get the lovely brown or black fluid from the rust and corrosion inside the system.
A way to see if it is the master cylinder causing this, if it happens often, would be to use a tie strap or bungee cord to pull the brake pedal up toward the dash. That would remove any pressure from the activating rod and let the pistons pull fully back in the bore.
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Sunday, July 28th, 2019 AT 2:38 PM

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