1989 K-1500 Brake Problems

Resetting a proportioning valve in a 2001 Ford Explorer typically involves bleeding the brake system to ensure proper brake pressure distribution. The proportioning valve adjusts the amount of brake pressure sent to the front and rear brakes to optimize braking performance. If you're experiencing brake-related issues or have replaced brake components, bleeding the brake system can help reset the proportioning valve. Here's how to do it:
**Tools and Materials Needed:**
- Brake fluid
- Jack and jack stands
- Wheel chocks
- Wrenches
- Brake bleeder kit or clear plastic tubing
**Steps:**
1. **Safety Precautions:**
- Park the vehicle on a level surface and engage the parking brake.
- Use wheel chocks to prevent the vehicle from rolling.
- Wear appropriate safety gear, including gloves and eye protection.
2. **Prepare the Vehicle:**
- Loosen the lug nuts on all four wheels, but do not remove them completely.
3. **Jack up the Vehicle:**
- Use a jack to lift the vehicle off the ground. Secure it with jack stands for safety.
4. **Bleeding Sequence:**
- Start with the brake caliper or wheel cylinder that is farthest from the master cylinder. In most cases, this would be the right rear wheel.
5. **Bleeding Process:**
- Have a helper pump the brake pedal several times and then hold it down.
- Loosen the bleeder valve on the brake caliper or wheel cylinder.
- Fluid and air bubbles should come out. Tighten the valve before your helper releases the brake pedal.
- Repeat this process (pumping, holding, opening, and closing the valve) until you see clear brake fluid without air bubbles.
6. **Repeat the Process:**
- Move to the next farthest brake caliper or wheel cylinder (left front, right front, left rear) and repeat the bleeding process.
7. **Check Brake Fluid Level:**
- Keep an eye on the brake fluid reservoir while bleeding. Make sure it doesn't run dry, as this can introduce air back into the system.
8. **Top Off Fluid:**
- After bleeding all the brake components, top off the brake fluid reservoir with fresh brake fluid to the recommended level.
9. **Test Brakes:**
- Lower the vehicle, tighten the lug nuts, and then fully tighten them in a crisscross pattern.
- Test the brakes to ensure they feel firm and responsive.
Bleeding the brake system is an important maintenance task, especially after working on the brakes or if you're experiencing spongy brakes. If you're unsure about the process or want to ensure proper brake system maintenance, consider seeking assistance from a professional mechanic.

Air in the system is what usually causes a caliper to lock up when everything else is functioning properly. If you can't get the air out of the system you will continue to have issues because when the brake system starts getting hot, the air expands inside the brake system causing the weakest brake to be applied. You will need to bleed the brakes once you fix the caliper that is not able to be bled. Remember, bleed the brakes from the farthest wheel from the master cylinder first and then continue to the nearest wheel last.

no
rear wheel brakes operate at different pressures because of the proportioning valve in the lines
you are correct that failing brake hoses can fail internally and lock the brakes on but I feel that that is not your problem
This is how disc brakes work
There is no check valve in the master cylinder as there is in a car with drum brakes so any fluid captured by pedal ( the exception here is if the car has read drum brakes in which case that section of the master cylinder will have a check valve )movement is pushed into the calipers and applies the brakes
Now on releasing the pedal , that fluid is allowed to return to the reservoir by a compensating port in the master cylinder
That port blocks up and the disc brakes remain on.
heat build up from the brake pads expands the fluid and so pushes the pads harder onto the disc( Lock on that you release by bleeding the calipers)
SO the problem will be in the master cylinder
having the brakes professionally flushed may relieve the problem for a period but a new master cylinder fitted professionally will fix the problem

Did air get into the master cylinder? If you can, try bleeding the master cylinder. The fact that you aren't getting any fluid out of the line suggests that the master cylinder isn't pumping fluid.

Master cylinders are (usually) on a split circuit system - that is, the front left brake is on the same line as the rear right. The front right brake is on the same circuit as the rear left.

A point to be aware of is when bleeding brakes/doing brake work and if the master cylinder runs dry, is that a seal inside the master cylinder can fail/twist over and not pressurise that particular line, even though it may pressurise the opposite brake line.

I'm in the UK. I have a 1998 Jeep Grand Cherokee 4 litre, which I am slowly rebuilding. Three weeks ago I fitted new front brake rotors, new front callipers and pads. I've been rebuilding cars for over 40 years now and have done countless brake overhauls.

.. and could I get a hard pedal after the job was completed? I must have bled the brakes three times a day for a week and couldn't get a brake pedal. I phoned a full time mechanic I know - he came and tried to bleed the brakes three times and couldn't get a hard pedal.

That's when you think 'The master cylinder was working before I started the job so it must be still working now'.

I fitted a brand new master cylinder and because some parts for older jeeps are hard to come by in the UK, I fitted a second hand proportioning valve. When I bled the brakes again the pedal became rock solid. Fixed.

You're probably fed up with your braking problem now ... and apparently this 'no fluid/brake pedal' is more common than you may think.

Try bleeding the master cylinder if you can. If you suspect that it isn't fully working - try an overhaul kit which is cheaper than a new master cylinder.

As for changing the proportioning valve .. that's your decision. My brakes now work though the truth is I don't actually know which was at fault as I changed both the master cylinder and proportioning valve at the same time. Maybe both were at fault, for whatever reason. I genuinely don't know.

The positive aspect is that you are doing your own work and know what you're doing. You're saving on labour charges.

Need year make and model. In most newer vehicles the valve is located in the master cylinder. It will not normally lock up the front wheels. It usually controls one front and one rear wheel at a time in the event of a brake fluid loss. If front calipers are locking up you could have seized caliper pistons/slide assemblies. The flex hoses may be deterioated internally due to contaminated brake fluid or the master cylinder may be defective

The hydraulic brake system must be bled any time one of the brake lines is disconnected or air enters the system. There are two ways to bleed the system; pressure bleeding or manual bleeding. Both procedures will be given here, although pressure bleeding requires the use of some fairly expensive equipment (a pressure tank) and is seldom used. Both methods are equally effective.The correct bleeding sequence is: left front, right front, left rear, and right rear. On master cylinders equipped with a bleeder valve, bleed the master cylinder last.
PRESSURE BLEEDING

1. Clean the top of the master cylinder, remove the cover, and attach the pressure bleeding adapter.
   
2. The spring-loaded plunger on the front of the proportioning valve must be depressed while bleeding. Wire or tape can be wrapped around the valve to hold the plunger in.
   
3. Check the pressure bleeder reservoir for correct pressure 20-29 psi (137-206 kPa) and fluid level, then open the release valve.
4. Fasten a bleeder hose to the wheel cylinder or caliper bleeder nipple and submerge the free end of the hose in a transparent receptacle. The receptacle should contain enough brake fluid to cover the open end of the hose.
   
5. Open the wheel cylinder or caliper bleeder nipple and allow the fluid to flow until all bubbles disappear and an uncontaminated flow exists.
   
6. Close the nipple, remove the bleeder hose and repeat the procedure on the other wheel cylinders according to the sequence.
   

MANUAL BLEEDING(see Figures 1, 2 and 3)An alternative to the pressure method of bleeding requires two people to perform; one to depress the brake pedal and the other to open the bleeder nipples.

1. Clean the top of the master cylinder, and then remove the cover and fill the reservoir with clean brake fluid.
   
2. To prevent squirting fluid replace the cover.
   
3. The spring-loaded plunger on the front of the proportioning valve must be depressed while bleeding. Wire or tape can be wrapped around the valve to hold the plunger in.
   
4. Install a box end wrench on the left front bleeder screw.
   
5. Attach a length of small diameter, clear vinyl tubing to the bleeder screw. Submerge the other end of the rubber tubing in a glass jar partially filled with clean brake fluid. Make sure the rubber tube fits on the bleeder screw snugly or you may be squirted with brake fluid when the bleeder screw is opened.
6. Have your friend slowly depress the brake pedal. As this is done, open the bleeder screw half a turn and allow the fluid to run through the tube. Close the bleeder screw, then return the brake pedal to its fully released position.
7. Repeat this procedure until no bubbles appear in the jar. Refill the master cylinder.
   
8. Frequently check the master cylinder level during this procedure. If the reservoir runs dry, air will enter the system and the bleeding will have to be repeated.

Hope helps.

faulty proportioning valve that runs off the mater cylinder

Could be a couple of problems, bad master cylinder (not bench bled properly or bad seal out of the box, I have had a few like that), proportioning valve seal, brake line not tight/sealed properly sucking air into system,bad caliper. First of all, are you losing brake fluid along with your pedal? Need to know that first. If you are, try to find where you losing it from, you will find your problem. There can be absolutly NO leaks in a brake/hydraulic system. If not, check that all lines are tightly seated and nuts are quite tight using a line wrench to get proper torque. If so, you can replace the master cylinder again (take old one back to store for new one under warranty) and be sure to thoroughly bench bleed. When bench bleeding, take your time, do not push plunger in too quickly, use a SLOW steady push until ALL bubbles, no matter how small have been eliminated. Tapping on the bottom of the cylinder while bleeding will help remove trapped air. Even a very small amount of air will take forever to bleed out at the calipers. If cylinder/all calipers/lines appear to be right, I would suspect the proportioning valve is faulty. To find it, follow brake lines from master cylinder to where they go into the valve. Replace. Hope that helps.

check at the proportioning valve--some have a pin that sticks out from the side, when bleeding the brakes try to push that pin back in. But first check to see why this happened--fluid leak to rear wheels, brake hoses cracked and air getting into the system??????

Start from right rear, then, left rear, right front, left front. Fill master cylinder. Have helper sit in car, have helper hold brake pedal down. open bleed screw. fluid and air comes out. close screw. release brake pedal. Continue until no air comes out. Move to next wheel. Keep an eye on master cylinder fluid level after each wheel.