Front brakes locking up!!!!!

[rockola1971]

Yah k you rockola! I haven't had to add fluid yet but from my research I'm beginning to agree. I will change the master cylinder today but I am unclear how to properly bleed. I have searched and it gives me the bench bleed method so I can do that but wouldn't I introduce air past the master cylinder once I disconnect lines at MC? So can I just do the traditional pressure bleed at each wheel afterwards or is there something more?

Bench bleed for the master cylinder is only for getting air out of the master cylinder. Once you remove the lines from the master cylinder then yes you will introduce air into the the front and rear brakes. Which will require a bleed of the whole system. You will find that these vehicles with ABS do NOT bleed near as easily as the old pre ABS autos. The ABS will trap air into the system which will cause the brake pedal to minimally get firm or not at all. So there are a couple ways to overcome this. The "easiest" is to gravity bleed it which takes some time and then take it out on rocks or grass and activate the ABS so it pushes the air toward the calipers then gravity bleed again. This could take 2-3 evolutions of this to get it bled.

 

[mossy oak]

I can't thank everyone enough. I thought I had hydroboost but I had a vacuum leak at pcv hose entering the valve cover. I replaced that and I swear the brakes are more firm. Coincidence?

 

[rockola1971]

LOL Thatll do it too. A vacuum leak will make a difference on a VACUUM BRAKE BOOSTER. Your brake booster is behind your master cylinder and the master cylinder bolts directly to it. A hydroboost system doesnt even remotely look like a vacuum boost system.

 

[mossy oak]

Well crap I did verify its hydroboost so not likely the vacuum leak helped. Maybe it was just wishful thinking. It's been a long long time since I've had to work on my own vehicles

 

[mossy oak]

If I slam on brakes, that's when they lock up and then I tap again and they're free. If I don't tap them the second time, the truck sits still. Anyway, besides that symptom they're just super soft. I don't see any leaks and maybe just a 2-3" residue below where the shaft enters the firewall from the inside of cabin.

 

[rockola1971]

That black circular object behind the master cylinder is a vacuum brake booster.


Directly behind the master cylinder with the lines coming off the top is a hydroboost with electric pump system.


So is your brake pedal firm or soft? Is your brake light illuminated on the instrument cluster?

 

[mossy oak]

Hey man yeah I feel like an idiot. I'm not well versed at all in hydroboost. But, the pedal is soft until right at the floor and it starts braking. And I do not have a light on. I seriously feel so lost on this issue. I feel like this truck is cursed. It's one thing after the next. The pedal still feels different after the vacuum pcv line was repaired. Coincidence for sure but I drove the truck today and the brake pedal felt a little stiffer. I don't get it.

 

[iamdub]

I'm wondering if you have two separate issues- one causing the soft pedal and another causing them to lock up. I'm leaning towards the master cylinder causing the soft pedal, but maybe it is causing the locking, too. After replacing it, if the locking up isn't resolved, you should at least have a normal pedal.

 

[mossy oak]

Thanks again! ILL Throw a MC ON IT AND GO FROM THERE I SUPPOSE!!!

 

[iamdub]

Be sure to bench bleed it!