Brakes locking up

LOSPINA

MEMBER
2012 HYUNDAI GENESIS
2WD
AUTOMATIC
92,500 MILES

I have the car listed above Coupe. My car has 2 major issues: the initial issue was that my car’s speed was not matching the RPMs. I would be driving on the highway going 65 MPH then out of nowhere the car would start to slow down no matter how hard I pressed the gas. This happened twice on different days but seemed to go away after pulling over and not driving the car for an hour or so. The second issue came a couple of days later where all my brakes started locking up and smoking. Not only was the car barely pushing forward but the second you let off the gas, it would come to a complete stop, I also noticed my brake lights stopped coming on when this occurred. A month before this started happening, I just had my front brake pads and my master cylinder replaced. After this started, we changed out the brake light switch because that’s the only relevant issue (on a very long list) the dealership diagnosed for me. The car is still acting up. I can’t drive it for more than a mile or so until it locks up. Please help. A mechanic friend of mine is suggesting we change out the whole ABS control module. Are there any other theories to solve this issue? Thank you!

4 Replies

KASEKENNY

MECHANIC
18,907 POSTS

Just to be clear, the brakes are not locking up all the time? If this is an intermittent issue then the likely issue is an ABS issue.

https://www.2carpros.com/articles/abs-warning-light-on-easy-repair-guide

This could be an issue with a wheel speed sensor so we should test these to make sure that is not causing the ABS to activate.

https://www.2carpros.com/articles/abs-wheel-speed-sensor-test

If everything checks out then this sounds like an ABS module.

https://www.2carpros.com/articles/how-to-replace-a-abs-controller

However, if the brake light and/or ABS light was coming on then we should check for codes.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run through this information and let us know what questions you have. Thanks

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Tuesday, June 15th, 2021 AT 7:06 PM

CARADIODOC

MECHANIC
33,871 POSTS

There's multiple things that can cause locking or dragging brakes, but with all of the dandy details you provided, this is likely related to the new master cylinder or the brake light switch adjustment. There's two ways to verify this. First, when the brakes are locked up, park on a slight incline or somewhere that you can easily push the car to know when the brakes are released. Shift to neutral, then either loosen the nuts holding the master cylinder to the power booster, and pull it forward about 1/8", or you can loosen the steel lines at the master cylinder. Either procedure will release the trapped pressurized brake fluid and let the brakes release.

If those procedures do let the brakes release, first look at the adjustment of the brake light switch. When the brake pedal is at rest, you should be able to pull it back a little more by hand. If you can't, the brake light switch is holding the pedal down. If that is far enough, the trapped brake fluid can't return freely to the reservoir. As the dragging brakes heat up, that heat migrates into the brake fluid causing it to expand. That applies the brakes even harder.

If the switch adjustment is okay, many import cars have power brake boosters with adjustable push rods. Those normally don't need to be readjusted when replacing the master cylinder, but someone may have tried to do that to solve a low brake pedal. If yours is adjustable, shorten it by about 1/16" to 1/8".

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Tuesday, June 15th, 2021 AT 7:16 PM

LOSPINA

MEMBER
6 POSTS

Thank you all for your replies. Seems the issue was the ABS. The mechanic bled the ABS first, put it in place then bled the brakes. He also had to use a computer to reset the codes. Car runs perfect now, actually responds better to accelerating than it did before this issue even started happening.

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Wednesday, June 16th, 2021 AT 6:46 AM

KASEKENNY