My brakes keep locking up and sticking?

Good afternoon.

Try this:

After driving it, go to the wheel and open the bleeder. See if it releases the brakes. If it does, the ABS control unit is the issue not allowing back flow to the master.

Roy

Just a question about this style of ABS system. If I pull the fuse and drive it will this have the same results on the return pressure?

No, that just disables the electronic portion of the system. Fluid still goes through the unit.

Roy

Thanks for your time and help on this, I was afraid it was going to be this. I should have went with my gut the first time instead of the proportion valve. But again thanks and I will give your advice a try and send you some kind of feed back. Have a great day.
Mark D

You are welcome Mark. Keep us updated.

Roy

Good evening Roy. I tried your advice and yes the bleeder did spit up a short stream of fluid and released the caliber from the rotor. My question before I put more money into this, the ABS electronic control module is what you state is the issue, is there any chance the ABS pump assembly could play a role in my problem or do you think it is just the ABS control module (Kelsey Hayes)? Thanks for any help you can give.
Mark D

It is the hydraulic unit that is the issue.

I attached a picture. It is the unit itself that has stuck valves.

Roy

That is what I was afraid of. By the time I finish with this I will have almost $1,500.00 in the brakes on a 1997 K 1500. But I really do appreciate all of your help and will highly recommend you guys to everyone I know.
Mark D

Make you a great deal on a truck minor brake issues, lol.

LOL. Thanks. Got a headache of my own.

Roy

Good evening Roy,
I just finished installing the new ABS pump and bled the system and brakes felt great. However, on the ride home about fifteen miles I started to get a very bad vibration from the right front wheel. It felt as though the wheel was coming off and when I pulled over that ever so familiar smell of cooked brake pads was over whelming. Another $500.00 into the brake system and I still have the same issue. Any ideas on this?

Did you flush the system of all fluid?

Roy

I applied the brakes hard while being towed with a chain, the engine wasn't running, the brakes are stuck on.

Hello,

It sounds like the brake master has not fully returned. To confirm the issue lets remove the mounting nuts for the master cylinder to see if the truck will move again. Please let me know

Front drivers side brake seems to be dragging. Gets worse the more you drive and wheel gets pretty hot. After letting off brake pedal to go you can feel it "sticking" for a few seconds. Also right rear keeps having air bubbles after hours of bleeding. Within the last few days we have replaced the booster,master cylinder, calipers,pads,shoes,and wheel cylinders. Brakes work and has a good pedal but what could be causing this?????

If you replaced the caliper and it still sticks, I would say that the rubber hose to the brake caliper needs replaced. They deteriorate inside and when you hit the brakes, fluid goes one way, but can't return. Thus, the brake sticks. Check that and let me know what you find.

I have a '90 Chevy 1500, and I recently replaced the front brake caliper because the piston was locked up and dragging. The new one went in with no issues, and I was bleeding the brakes, when I realized I needed new sealing washers on the banjo bolt, because it was leaking. So those were replaced and I bled them again, and once again the piston froze up. I checked it today, 2 days later, and the rotor spun free. I pumped the brake, and they locked up again. So obviously it's not the piston, but something else in the brake system. How can I diagnose the problem?

Check brake hose to that caliper, Over time brake hoses can break down inside and become essentially a one way valve

After doing some research I think that may be what is happening. Thanks for your reply.

Your welcome

When pushing on the brakes, the rear brakes are more aggressive than the front brakes. It gets real interesting when it is slick out as the back breaks lock-up and there is limited front brakes.

These are hydraulic assist brakes that came in these things.

Brakes are new this summer, front calipers are new also. Issue was present before replacement. There are no liquids on the drums or pads. Bled the front brakes.

There is a ABS control module and ABS Hydraulic Unit, I don't know if there is a proportioning valve in this or not.

Any help on ideas on what this could be would be great.

That really sounds like brake contamination. You don't have to actually see any liquid. Even very small amounts will embed into the shoes along with brake dust and ruin the shoes and the drum surface. If the shoes look dark in color at all, then they are likely contaminated. Look at the backing plate carefully for any apparent dark spots to indicate oil residue from either the brake fluid in the wheel cylinders or gear oil from the differential seals.

when i pump the brake up 4 or 5 time and let off. the rear brake want release but when i open the bleeding valve on the right rear wheel the rear brake then release. i disconnect the rubber brake hose at the rear and push a small wire through it and blow air through it. it seem like the hose is opening i don't think the fluid is returning back to the master cylinder the fluid is leaving the master cylinder but seem like the fluid is not returning back to the master cylinder when let off the brake. what all could be the cause?

You had the right idea by opening the bleeder screw, but now when it acts up again, loosen the steel line at the master cylinder. If the trapped brake fluid releases from there, you either have a brake light switch that's misadjusted and holding the brake pedal down a little, or the brake fluid has been contaminated with a petroleum product.

I did open the steel line at the master cylinder 1 or 2 turn but the rear brake did not release. what should i do next?

That is the best thing I've heard all week. That tells us the brake fluid is not contaminated causing the lip seals to grow past the fluid return ports.

Next step is to open the system at various places to see where the trapped fluid will release and where it won't. A lot of trucks and minivans have height-sensing proportioning valves, but I don't see one listed for yours. If you have anti-lock brakes, look for the line coming out of the hydraulic controller that goes to the rear brakes and loosen it there. If you don't have anti-lock brakes, you'll have a combination valve on the frame right under the master cylinder. The next place would be where the steel line connects to the rubber flex hose over the rear differential.

By the way, the anti-lock brakes would be for just the rear wheels. That hydraulic controller design gives very little trouble but it's possible for a valve to corrode apart and block the fluid return passage.

what does the combination valve look does it have one tan wire connected to it?

If you don't have rear-wheel-anti-lock brakes, follow the two steel lines from the master cylinder down to the combination valve on the frame rail. It will have one wire for the pressure-differential valve inside the assembly. There will be three additional steel lines, one for each front wheel and one for the rear pair. Loosen the one at the rear to see if the brake fluid releases.

So if i loosen the steel line at the rear and the brake fluid release what is that problem? and if the brake fluid don't release when i loosen the steel line at the rear what is that problem? about the one wire that run to the combination valve i check for voltage at the wire and the wire didn't have any voltage how to fix that?

This is just one long circuit for the brake fluid to flow, and somewhere along it is something that's blocking its return. When you open it someplace and the fluid and brake releases, you know everything from that point back is okay. When the fluid doesn't release, you still have something in it that has the blockage in it. Just keep opening the system at various places until you narrow down the location of the restriction.

That wire wont have any voltage until the ignition switch is on. It just goes to the pressure differential switch. That turns the red brake warning light on when there's a leak in one of the two hydraulic systems. That doesn't have anything to do with the rear brake not releasing.

Can the Combination valve be took apart and check if that the problem that causing the rear brake not to release?

I loosen the line at combination valve that run to the rear brake and the brake realeses this line is at the bottom of the combination valve but the lines that run from the master cylinder to the combination valve when i open them brake don't release so is the combination valve bad not letting the fluid return back to the master cylinder?

It would appear you solved the problem. I've never actually run into that, but given all the stuff that's in that assembly, it's understandable that it could cause that problem.

You aren't going to find this valve at the dealership, partly because if its age, and partly because there's too many variations. Because they DO have such a low failure rate, you'll have a real good chance of finding a good one in a salvage yard. Keep in mind though that the proportioning valve, which sends brake fluid to the rear and limits fluid pressure to reduce rear-wheel lockup, was carefully-calibrated to your specific truck's weight distribution and weight transfer during braking. If you can find a part number on your valve, and you find one in a salvage yard with the same number, you're home free. If there's no number on them, look for one on a truck that is the same as yours. That means the same year, same engine family, same wheel base, and same options. That valve will be different between a truck with air conditioning and one without because of the difference in weight on the front. A truck with a V-8 engine will have a different valve than one with a V-6. A dually rear axle or extended cab will be different too.

Sorry I overlooked your first reply. The combination valve can be taken apart but I would only do that to learn how they work or how they're built. We don't normally fix them so I don't know if there are critical adjustments or seals that could leak. If you do pull it apart, it would be interesting to know if you find anything obvious. Also, given that they do have such a low failure rate, it doesn't pay to go through all the work of removing it, then to put it back on and have it do the same thing.