Front brakes have been locking up

Hi,

Both sides are locking? Do you have to press hard for it to happen or does it happen with light braking? Does the vehicle pull one way or the other when you apply the brakes? This happens when the brake booster push rod is adjusted out too far which does no allow the brake master to return fully holding the brakes on . To confirm the issue loosen the brake master mounting bolts 3 turns to see if the car starts to roll again, if so remove the master and adjust the booster push rod inward. Also a brake flex hose can come apart internally causing a short of check valve in the system but this is usually isolated to one brake either front or rear.

You have replaced nearly everything. Since it worked properly for a month, I have to ask, what was the last part you installed that took care of the issue for that long? I hate to assume, but I have to ask if the pads were replaced as well. You didn't indicate them or the brake hardware on the caliper mount.

Here is a link that shows in general how front pads and rotors are replaced. Take a look through it and see if there is anything that could possibly have been missed. This is a general link, but it does cover everything.

https://www.2carpros.com/articles/how-to-replace-front-brake-pads-and-rotors-fwd

Also, I noted that the ABS module was replaced. Interestingly, that should be preventing a lock up.

Let me know.

Joe

Just to jump in, I have seen this condition before. Remove the master cylinder and inspect inside the booster for brake fluid. If the old master cylinder was leaking, chances are the vacuum from the booster was drawing in brake fluid. That will cause the front calipers to lock up. Inspect the booster and let us know the results please.

Thank you for the suggestion. I will check it out.

Both sides lock up at the same time and does not pull to one side or the other. I don't have to push on the brakes for them to lock up. The first time it happened the truck was parked with the engine running and when I tried to back out of parking place the brakes were locked up.

The brake pads and rotors have been replaced. Every time I fix something the brakes seem to work for a while but then the problem comes back. I had a brake shop replace the master cylinder, hoses, and calipers first and worked for a couple of months. I replaced ABS control module next and worked for a few weeks. Replaced proportioning valve and worked for a couple of weeks until battery died, when I replaced battery brakes locked up. Replaced brake lines from calipers to frame (didn't look like the brake shop did this when they replaced master cylinder - brake shop not very helpful) and brakes worked for about 6 weeks. This weekend I replaced the wheel speed sensors and brakes are working for now.

I think there may be an electrical issue and something shorts out causing the proportioning valve or the ABS control module to malfunction, then pressure builds up in the system.

Let me know if you have any suggestions and thank you for replying.

Did you look inside the booster for brake fluid contamination?

I have not done that yet, before I had the brake problem I replaced the hydro boost unit because it was leaking power steering fluid. Then after I starting having the brake problem I replaced the master cylinder.

The hydro boost system won't have a vacuum booster. Do the brakes seem to lock up slowly as you drive? Have the brakes ever been locked up after being parked?

Joe

The first time the brakes locked up I was parked with the engine running. After that the brakes lock up when I am driving (not applying the brakes). You can feel them gradually squeezing the rotors. I have to turn off the truck for an hour or so for the pressure to be released or I have to crack open the bleeder valves.

Honestly, I feel the brakes are dragging a bit when you first start driving. What often will happen is this. As you drive the vehicle (brakes off) the dragging will create heat. The longer you drive, the hotter they get. Brake fluid will expand under extreme heat. As it expands, the brakes apply a little at a time until they lock. After they cool off, they release again (or at least release enough to drive it again), or if you open the bleeder, it releases the pressure.

What I need you to do is this. Safely lift the front of the vehicle when it is cold. See how much resistance there is when trying to turn the front wheels. If there is little, have a helper press the brakes and release them. Check again. If there is more resistance, they are not fully releasing which can cause this.

Do that and let me know what you find. Also, let me know if anyone was working under the dash on a brake light switch or anything near it.

Joe

I disconnected the brake pedal when I replaced the hydro boost unit because it was leaking power steering fluid. I did this 6-12 months before the brake problem started.

When I replaced the wheel speed sensors a couple of weeks ago I had to remove the brake pads, rotors, and calipers. I had to open the bleeder valves to compress and remove the calipers and they were rubbing a little.

I feel something is hanging up and causing it to slowly do what you are describing. Since you had to open the bleeder at the caliper, I need you to try something. Open slightly open the lines at the MC and see if they release. If they don't, we have an issue between the two. It isn't uncommon for a rubber brake hose to fail and only allow fluid to flow one direction. As a result, the caliper can't release.

Try that and let me know what you find.
Joe

All the rubber brake hoses have been replaced. The brake shop replaced some when I had them put in the master cylinder and I put in new ones from the calipers to the frame.

I have been keeping track of when the brakes lock up since my last text. The brakes have locked up 3 times. It has rained a lot here in Dallas this month. Each time the brakes have locked up I felt the tires slip on the wet pavement (starting from a stop or going around a turn) and the service stability light came on. Before the service stability light only came on sometimes.

To me it seems like the problem is somewhere between the proportioning valve and the ABS control module. I installed a new proportioning valve so probably not that. I installed a used ABS control module ($250.00) instead of a new one ($1,600.00). Same problem so both control modules have same malfunction? Or could there be some kind of wiring problem between the control module and proportioning valve? The clip that holds the plug into the proportioning valve is broken. Could that cause the problem? I have tried unplugging the proportion valve and driving but doesn't seem to do anything. The proportioning valve controls how much of the brake fluid goes to the front or back brakes. (Right?) If I disconnect the proportioning valve and then make the wheels slip and the brakes don't lock up and the service stability light comes on, is the problem in the control module?

Thanks for your help!

You are correct regarding the purpose of the proportioning valve. So this only happened when it rained. Make one think it is an electrical issue. All connections at the module are clean and tight?

Joe

The only connection problem is the broken clip on the plug at the proportioning value. The connections to the ABS control module looked fine when I changed out modules. Most of the wiring runs through conduits and can't see it. Yesterday when I drove the truck it wasn't raining but there were wet places from rain earlier in the morning. I purposely made the wheels spin and the brakes locked up and the service stability light came on.

That is odd. It must have something to do with the control module. Do you have a scanner that can communicate with the ABS module? Also, just to reconfirm, if you open the bleeder at the caliper, it releases the brake, correct? Also, you are certain there are no diagnostic trouble codes related to the ABS or Traction Control?

Joe

I don't have a scanner. When I open the bleeder valves the pressure releases. I had to remove calipers and rotors to replace wheel speed sensors. Had to open the bleeder valves in order to open the calipers enough to get them off. The check engine light goes on and off but has something to do with the fuel system and has been doing it since I got the truck 140,000 miles ago. As far I as I know there are no other trouble codes.

I really like the truck, the way it drives and how comfortable it is, but it is probably time for a new (used) one. This is the third Tahoe I have had over past 20 years.

What is your opinion on having a truck rebuilt, new (rebuilt) engine, new brake system, fresh paint, interior, etc?

Hi,

The only issue with rebuilding is you won't end up with all GM parts. Not saying others are bad but it does make a difference. Now, I don't know where you are located. I know here, in PA, rust destroys vehicles because of products used on the roads during winter. Once a vehicle hits about 10 years old, frames, floors, and structural components really get bad.

So if you were to do it and you live in this type of area, make sure the foundation of the truck is good. The GM vehicles around here are starting to have frame problems. Next, you have to keep in mind that everything on the vehicle has a lot of miles. Components such as bearings, sensors, modules and so on may work today and be bad tomorrow. That is one of my biggest concerns because to replace everything to rebuild the vehicle, it would be cheaper to buy a new one.

In my mind, you would most likely be better off finding one with low mileage.

Let me know if you have other questions.

Joe

Ihave a 02 tahoe & my brakes keep getting stuck. Unable to drive suv because brakes get stuck. Have replaced callipers & still having to bleed brakes about twice a day. Could I have a hole in the brake line causing air to get in???

With a hole, you'd have the opposite problem. The brakes would not apply. When you can catch the brakes locking up, crack open the steel lines at the master cylinder, or open the bleeder screws. You're looking for a point at which the fluid pressure can be relieved and where it can't. If the brakes release at the master cylinder, suspect brake fluid contaminated with petroleum product or the brake light switch is misadjusted and holding the pedal down a little. Either of those will cause the fluid return ports to be blocked in the master cylinder.

caradiodoc

I have been having problems with the right front brake on my tahoe.It started with the right front locking up,once I cked it I found the brake line going to it had a hole in it.I repaired it,replaced brake pads on both sides and bleed brakes.It was fine for about a month.Then it (rt ft brake),started locking up after brakes applied.I replaced right front caliper last sunday and it seem to be fine untill friday coming home from work.I noticed some drag and once home it was extremly hot.Cked it this morning it is very slow to release.Cked fluid(ok) and cked for visibly leaks,none found.Help!!!!!

If the caliper is good but not releasing, make sure the slides are loose, the piston is easy to depress, and if they all look good, I would try replacing the rubber brake hose to that caliper. I have seen them deteriate to a point where they allow pressure to be applied but wount let the brake fluid return to release the caliper. Hit the brakes and if it doesn't release, open the bleeder to see if it releases then. If it does, chances are the hose is the problem.

My brakes lock When i turn.

That is not much information to go on. What are the symptoms? Do you have to turn fully to the side or just part way? What do you do to get the brakes to let go?

Turn fully. I have to put it on park then back to drive. So it can drive it.

I have big rims on it and i made a u turn and the brakes lock.

Hi when I made a u turn my brakes lock. I had to put it on park then back to drive. What could it be?

You did not list if it is a four wheel drive. If it is, a common problem that shows up when turning is a binding outer front universal joint. That will stop some vehicles and it will force the steering wheel back to center.

Obviously tires that are too big could rub on the inner fenders, but you would hear that. Also, simply straightening the steering wheel would solve that.

The next thing is to determine if this is a mechanical problem or a hydraulic problem, meaning trapped brake fluid. Typically trapped brake fluid only occurs after the pedal was pressed, then the brakes stay partially-applied, they get hot, the trapped fluid heats up and expands, and that applies the brakes harder. To locate the restriction, which is usually caused by a rubber flex hose, you have to stop on a slight incline, shift to neutral, place a block about a foot downhill of a tire, (so you don't look funny running after the vehicle), then you open the system at various places to see where the fluid is being trapped. Caliper bleeder screws and the steel lines at the master cylinder are the easier places to do that.

Mechanical problems that let the brakes lock are usually caused by rear drum brakes. A parking brake cable rusted tight in the partially-applied position will cause those shoes to grab the drum and self-apply. Backing up will let them release, but that doesn't have anything to do with turning the steering wheel.

Some vehicles have "bump stops" which are mechanical blocks that limit how far the steering system can be turned. If those have rusted off or were removed, over-turning can cause binding.

Hello,
I have a 1997 4x4 Tahoe. - 5.7 The other day when I drove it, it came to a complete slow stop on it's own. When I tried to force it to move, I went about 30 feet and the brakes started to smoke along with that wonderful 'burnt brake' smell.

All 4 wheels seem to be locked up. If I let it sit overnight, they release, but when I try to drive it they lock up again. It happens slowly, it's not a sudden neck jerking stop. I took out the ABS fuse ... didn't help. ANYONE have any ideas as to what this might be?

Thank you.

with all the brakes locking up the master cylinder could be going bad and sticking. When it happens try releasing the pressure from the master cylinder by loosing the line comming out as one would bleed the cylinder and see if the pressure releases. if it does you need a master cylinder.