I have a 2001 Sonata GLS. I'm having a problem where the brakes on all four wheels lock up while driving. Fun ha? It hapens after a few minutes of driving. Before they lock up the brakes operate normally. When this happens the brakes are applied, the petal becomes hard and pressure is applied to all four wheels and won't release. If you stop the car and turn it off for 10-15 munutes the problem goes away. I've inspected all four wheels disk brakes and everything looks fine with less than 50% pad wear. I spoke to the service manager at my local dealer and he recommended that I investigate the master cylinder. This seemed to make sence since it's common to all four wheels. Bye the way it doesn't have ABS. I removed and inspected the master cylinder and didn't find anything obviously wrong with it but I replaced it anyway. After a short trip to the store to test the brakes it happened again confirming that the problem isn't he master cylinder.

At this point I'm suspecting soming with the pedal linkage or the vacuum booster. Has anyone else experienced this and if so how did you solve it?

Bob Sonata

 

If you replaced the master cylinder, then you bled the brake system obviously.

If it was pedal linkage, it would be pretty obvious. The pedal wouldn't return.

Could be the brake line splitter has got dirt in it, but you did bleed the brakes lines out.

Vacuum booster is a possibility, the check there is to isolate the booster from the vacuum. This will make it hard to brake, but if it doesn't lock up, then you know that's the problem.

 

Thanks for the reply,

What is the brake line splitter? The master cylinder has four lines that go to the four wheels. I didn't see any other components. I'm going to disconnect the vacuum booster and drive it for a while to see if this happens again. it's difficult because it happens somewhat infrequently.

 

Ah, no splitter. Ok, my Elantra has a splitter. Two lines go into the master, then there's a splitter thing underneath. Well then, rule out the splitter.

So you are faced with either the vacuum booster problem or the master cylinder, nothing else to fail. And you changed the master so...

 

my parents have a 2001 santa fe that they are having same problem with.I was wondering if booster fixed problem,theirs has abs though

 

My son has the same problem, infrequently brakes lock on after braking, 5-10 minutes later they release and you can drive on with no problems for a few days then it happens again. I pulled the brakes apart, only front left brake pads worn out and that side rotor has many fine hair line cracks, so I thought maybe the caliper had stuck. I have put in a new repair kit in the caliper and I am half way through replacing 2 front rotors and pads when I saw this thread. I didn't really see any problems with anything other than worn brake pad and faulty/damaged rotor so I am not convinced the problems is in the parts I am replacing. The worn out pads I believe has happened because my son drove with brake locked on, the rotor overheated which caused the hairline cracks.
Also all slide pins on calipers were well oiled so they shouldn't have stuck.
But something has caused the brake to lock on, what I don't know.
I am going to clean lines by refilling with new brake fluid and hope it is all fixed.
I drove the car around for a bit before doing repairs but found nothing wrong, a real mystery!

Love to hear any comments on this issue.

colsan