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Discussion Starter #1
2008 Hyundai Accent
~105k miles
Up to date on scheduled service

So my wife was driving today, in mildy wet conditions, around a turn at low speed. This occured during light acceleration to prepare to pull onto a highway, so the brake pedal was not engaged. She says that she felt both front wheels lock up simultaneous, and unexpectedly. The rear wheels continued to roll, but caused the car to slide sideways off the road. The front brakes did not release for several additional minutes. Then she pulled off the side of the road and drive ~1/4 mile to park the car at our home.

From researching on the internet, I saw that there may be a problem with the brake master cylinder, or possibly contamination in the brake fluid. The brake fluid has not been serviced recently, and the brakes are a few months old. No other problems or strange noises we have noticed before this. The service center is not able to take us in for a few days, and given the safety concerns, I do not want to service it myself without being able to definitively diagnose what the issue is. The last thing I want is to service "A" and find out the hard way it was a problem with "B".

I was hoping for two things: First, has anyone had this issue and have an idea of what it could be? Second, I would like suggestions as to how I would confirm that diagnosis, and then initiate the repair.

Any help would be appreciated. Thank you in advance.
 

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This sounds like a master cylinder issue. Previous experience I had a buick do the same thing. Locked up then released. This is very dangerous. If your brakes are new not to bad mouth the place you got them serviced but if then pressed back the pistons in the calipers to release them without opening the bleeder screws the pressure going back into the master cylinder can damage the seals in the master cylinder. I have brake videos on my site you can check out to see what I am talking about. I always brake the bleeder then press in the caliper piston and take the cap off the master cylinder to allow pressure to escape. This is why I hate others fixing my car. I dont think its brake booster related. Does your car have abs? Mine does not.

Brake drag
1. Brake pedal free play (Minimum)
2. Parking brake lever travel (Out of adjustment)
3. Parking brake wire (Sticking)
4. Pad or lining (Cracked or distorted)
5. Piston (Stuck)
6. Piston (Frozen)
7. Return spring (Faulty)
8. Booster system (Vacuum leaks)<check this one as well
9. Master cylinder (Faulty)
 

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For simple checking of the brake booster operation, carry out the following tests :

1.
Run the engine for one or two minutes, and then stop it. If the pedal depresses fully the first time but gradually becomes higher when depressed succeeding times, the booster is operating properly, if the pedal height remains unchanged, the booster is defective.



2. With the engine stopped, step on the brake pedal several times. Then step on the brake pedal and start the engine. If the pedal moves downward slightly, the booster is in good condition. If there is no change, the booster is defective.



3. With the engine running, step on the brake pedal and then stop the engine. Hold the pedal depressed for 30 seconds. If the pedal height does not change, the booster is in good condition, if the pedal rises, the booster is defective. If the above three tests are okay, the booster performance can be determined as good. Even if one of the above three tests is not okay, check the check valve, vacuum hose and booster for defect.



Vacuum Hose (Check Valve)

Inspection

1. Disconnect the brake booster vacuum hose (check valve built in) (A) at the booster .


2. Start the engine and let it idle. There should be vacuum available. If no vacuum is available, the check valve is not working properly. Replace the brake booster vacuum hose and check valve and retest.

 

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Discussion Starter #4
ikilledbarbie, would the issue be resolved by replacing the master cylinder or would this have caused additional or systemic damage?
 

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A faulty master cylinder will not damage other brake parts. If your booster is ok before condeming the master cylinder have brake rubber lines checked. Double check the caliper guide pins are not seized in the extension position. Im not a certified mechanic but always refer to the hyundai service manual for tests and replacement. Do not mess with this as your families safety is more important. You can try these booster tests and you can jack car up. Set rear energency brake. Block back tires and while car is running put car in neutral. Shut car off. Key will not come out. Grab tire and spin clockwise. Compare resistance on both apply brake then release. Do they feel the same. This will test the release of the caliper piston. If it does not release take tire off . Before you do this press brake start car and put in park. Then remove tire and apply vacuun like in my videos on brakes. If you do not own vacuum tool have your wife apply brakes. Open bleeder. As the fluid come out the pedal will sink. Once the bleeder is open does thr caliper piston release? If your brake is sticking and after the bleeder is open I would suspect a colapsing brake line. If it still does not release it bad caliper piston.

Before running these bleeder tests open brake fluid cap to allow pressure to release. Top off fluid to the max line. Wife pedal in open bleeder. Pedal down have her hold and close bleeder. Pump pedal till firn and repeat. This prevents air re enteting and bleeds air out.

You can see many videos online on master cylinder testing brake flush and other videos.
 

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2008 Hyundai Accent
~105k miles
Up to date on scheduled service

So my wife was driving today, in mildy wet conditions, around a turn at low speed. This occured during light acceleration to prepare to pull onto a highway, so the brake pedal was not engaged. She says that she felt both front wheels lock up simultaneous, and unexpectedly. The rear wheels continued to roll, but caused the car to slide sideways off the road. The front brakes did not release for several additional minutes. Then she pulled off the side of the road and drive ~1/4 mile to park the car at our home.

From researching on the internet, I saw that there may be a problem with the brake master cylinder, or possibly contamination in the brake fluid. The brake fluid has not been serviced recently, and the brakes are a few months old. No other problems or strange noises we have noticed before this. The service center is not able to take us in for a few days, and given the safety concerns, I do not want to service it myself without being able to definitively diagnose what the issue is. The last thing I want is to service "A" and find out the hard way it was a problem with "B".

I was hoping for two things: First, has anyone had this issue and have an idea of what it could be? Second, I would like suggestions as to how I would confirm that diagnosis, and then initiate the repair.

Any help would be appreciated. Thank you in advance.
I'm having this same problem did you ever figure out how to fix this?
 
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