Ok this is on my 97 F150. I had a leak in my line because of age and rust. I replaced all the hard lines and rubber lines. I got a new master brake cylinder, bench bled it. Installed everything and for the next 3 yours trying to get the brakes to keep pressure. The pedal does not get hard.

We bled the lines in the correct order and with the car on and off.

Now, when you have the car onand you remove the vacum line from the brake booster I have a very nice feeling brake pedal and the brakes work. As soon as you plug the vacum line in, the pedal looses pressure. It still sayes up but if you press down it goes to the floor.


I thouhgt maybe it was a bad Master brake cylinder, so I put the old one back on. With the old one on, i get the ABS and BRAKE light that stay on. Tried bleeing it several times too with the car on and off.

I did adjust the boost rod a little.

Any suggestions what to check or the cause could be?
I'm not leaking any fluids and when you bleed the brakes you get good fluid.

Latly, I dont think this has anything to do with it, but does anyone know why the brakes lines have the swirl effect on the front lines? Instead of straight down from the Master Brake Cylinder.

Thanks, looking forward to hearing back.

 

The booster check valve is most likely stuck open. Pull it out and make sure it's working properly. I did the same on my 98, - gutted all the lines, hard line and rubber, -master cylinder as well. BUT, I didn't replace the booster or adjust boost rod, adjusting that rod is a no no lol. However, I replaced the booster (air assist) check valve. Mine was hanging just a little. You'll loose most if not all of your boost air and it can't build pressure if that valve is open, -know what I'm sayin? So pull it, check it out.

Good Luck

 

No offense jbrew... but no, that is not the problem.

The reason the pedal feels "better" when he removes the vacuum line is that he gets no boost so the brakes feel solid. But he's just not building much pressure.

Once you put vacuum on the booster it boosts the pedal force and causes the pedal to drop when you press on it... this indicates problems with the MC or a bad bleed.

Since you tried 2 MCs with the same results, I'm guessing its a bad bleed. Perhaps you should consult a mechanic to ensure you are bleeding properly? Be sure that you don't "bounce" the brake pedal when you are bleeding... if you press down to fast it will bounce at the bottom and suck air back in.

Did you use all OEM lines or did you bend your own? Perhaps you have some locations in the pipe where the air gets trapped?

The other possibility is that you have a very small leak somewhere... have you inspected every single connection point? It only takes a tiny leak to make the pedal drop away.

as for the "swirl"... I'm not sure what you are saying... can you post a picture?


One other option is to do a vacuum bleed. Put a vacuum pump on the reservoir opening and let it pump for 10 minutes to suck any and all air out...

 

mkosu04 Alright, so that's not a check valve on the booster ? Or is it and it's functioning properly ? What are you saying is wrong with my post ? There's no way in hell it could be the booster valve ? I just want to be clear.

I guess you condone rod adjustment for a new master install as well, correct ?

_________________________________


Midnightride42 - You bent and flared your own right ? That's the only way to do it that's affordable. He's right about leaks and bleeding. Also , you can't use self bleeders on these or a cheap vac tool. I found that out quite awhile ago. I had a bad flare (my fault) in the back, -that short 12" (approx). I just made up a new one real quick, then bled it again.

I have heard it can be a PITA. BTW, I used all original fittings over again coming from the Master and one at the back I believe @ the breather block.

I have pics of the procedure , step X- if that would help. I did mine two winters back. You'll be glad you did once you get it worked out, - feels like a new one all over again

Good Luck

 

yes I flared and bent my own lines.
where is the check valve for the brake booster?
on a other forum someone mentioned the RABS module block needs bled...i have abs since the light comes on....but the location he told me there is no such module. I have a block with a sensor and brake lines going to it below the MC, but it does not have bleeder valves.

if you could show me where or post a pic of the booster valve I'll check that. does the booster need removed for that?

going to bleed the system again.

seems like we got air bubbles in the MC when we pump the brakes. We got no leaks...no fluid coming out.

it's very frustrating having great pedal feel but when you start the car it goes to the botttom. When the car is on and we bleed the brakes the pedal never gets hard......the check valve you describes would make since and knowing where it is and what it looks like would help out a lot.....also if it's stuck its needs replaced right? Is that part of the Booster?

Thanks again......just weird I didn't have brake issues till one of the lines blew and I decided to replace them all.

 

You don't have a RAB's so don't worry about that. You have a proportion valve, but nothing special needed to bleed. You can't miss the check valve, it's right the booster. It's the only piece your air assist line connects to.

Mines Blue on the booster w/line attached. -



Pic was taken right after I finished.

 

Jbrew....what is the harnes that plugs into the bottom of the proportion valve? Just asking because I think all my issues are caused by a striped hole in the proportion valve. I hooked a vacum bleeder pump onto the bottom fittin (seen in your pic above) and got a lot of air coming out. I did the same on the MC and got very little. After I took the lowest fitting out I saw some threads...so either the aluminum block is screwed up or the brake line fitting. As of right now I think that's cauing my issue.

I'll report back when I get that fixed. I hope I can find one at a local yard, because new/rebuild I think they are right around 200. Are there any other models I can use it off? Explorer/navigator/expeditions? I would think yes, but wanted to check. Thanks.

Also, I sprayed wd40 into that fitting as you mentioned. It didn't help any, but atleast I'm rulling things out.

Thanks again!!

 

Are you talking about the aluminum block below ? That's the proportion valve.

Hang on , I'll look it up @ service real quick, I did mine 2 years ago, my memory has faded a bit since then lol.

 

Here's a little explanation of things, there's more, I'll keep looking -



The power brake booster:

Is a single or tandem diaphragm, vacuum-assisted power brake booster.
Reduces brake pedal pressure and travel distance.
Is located on the LH side of the bulkhead in the engine compartment, between the brake pedal (2455) and brake master cylinder (2140).
Will not operate if vacuum is restricted or if any of the vacuum- related power brake components fail.
Is replaced as an assembly.
If the power assist fails, the brake system will continue to operate with increased brake pedal effort.


Hose and Check Valve

The power brake booster check valve:

Is located on the front of the power brake booster.
Is positioned between the power brake booster and the power brake booster hose.
Closes when the engine (6007) is turned off.
Is part of the power brake booster, and is not replaced separately.
In the closed position, traps engine vacuum in the power brake booster.
Reserve vacuum allows several power assisted brake applications with the engine off.

 

I guess you need = PERFORM the Brake Master Cylinder Component Test in this section. Right ? You want that info ? I'm still looking for the P-valve layout.

 

Component Tests

Preliminary Checks

NOTE: Always check the fluid level in the brake master cylinder reservoir before performing the test procedures.

If the fluid level is not at the MAX line on the brake master cylinder reservoir (2K478), add Ford High Performance DOT 3 Brake Fluid C6AZ-19542-AB or DOT 3 equivalent fluid meeting Ford specification ESA-M6C25-A.

WARNING: USE OF ANY OTHER THAN THE APPROVED DOT 3 BRAKE FLUID WILL CAUSE PERMANENT DAMAGE TO BRAKE COMPONENTS AND WILL RENDER THE BRAKES INOPERATIVE.

If a brake is locked and the vehicle must be moved, open a bleeder screw at the locked wheel (1007) to let out enough fluid to relieve the pressure. Close the bleeder screw. This bleeding operation may release the brakes but will not correct the cause of trouble. If this does not relieve the locked wheel condition, service the locked components before proceeding.



Brake Booster Functional Test

Inspect all hoses and connections. All unused vacuum connectors should be capped. Hoses and their connections should be properly secured and in good condition with no holes or collapsed areas.



Brake Booster Operation Check

Check the hydraulic brake system for leaks or insufficient fluid.
With the transmission (7003) in NEUTRAL, stop the engine (6007) and apply the parking brake control (2780). Apply the brake pedal (2455) several times to exhaust all vacuum in the system.
Apply the brake pedal and hold it in the applied position. Start the engine. If the vacuum system is operating, the brake pedal will tend to move downward under constant foot pressure. If no motion is felt, the power brake booster system is not functioning.


Brake Booster

Remove the vacuum booster hose from the power brake booster and check the valve connection. Manifold vacuum should be available at the check valve end of the vacuum booster hose (2A047) with the engine at idle speed and the transmission in NEUTRAL. If the manifold vacuum is available to the power brake booster (2005), connect the vacuum booster hose to the power brake booster and repeat Steps 2 and 3 of the Brake Booster Operation Check. If no downward movement of the brake pedal is felt, replace the power brake booster.
Operate the engine a minimum of 10 seconds at fast idle. Stop the engine, and let the vehicle stand for 10 minutes. Then apply the brake pedal with approximately 89 N (20 lbs) of force. The brake pedal feel should be the same as that noted with the engine operating. If the brake pedal feels hard (no power assist), replace the check valve and retest. If the brake pedal feels spongy, bleed the hydraulic system to remove air; refer to Section 206-06 for Hydraulic System Bleeding.


Check Valve

The function of the power brake booster check valve (2365) is to allow manifold vacuum to enter the power brake booster and prevent the escape of vacuum in case manifold vacuum is lost during sustained full throttle operation.

To test the function of the power brake booster check valve:

Start and run the engine for at least 10 seconds.
Operate the brake pedal to check for power assist.
Disconnect the vacuum booster hose from the power brake booster. Do not remove the check valve from the power brake booster.
There should be enough vacuum retained in the power brake booster for at least one more power-assisted brake operation.


Brake Master Cylinder


Normal Conditions

The following conditions are considered normal and are not indications that the brake master cylinder is in need of service.

Condition 1: During normal operation of the master cylinder, the fluid level in the brake master cylinder reservoir will rise during brake application and fall during release. The net fluid level (i.e., after brake application and release) will remain unchanged.

Condition 2: A trace of brake fluid will exist on the booster shell below the master cylinder mounting flange. This results from the normal lubricating action of the master cylinder bore and seal.

Condition 3: Fluid level will decrease with pad wear.


Abnormal Conditions

Changes in brake pedal feel or travel are indicators that something could be wrong in the brake system. Refer to the Symptom Chart for abnormal condition diagnosis.


Bypass Condition Test

Check the fluid in the brake master cylinder (2140). Fill the brake master cylinder reservoir if low or empty.
Observe the fluid level in the brake master cylinder reservoir. If after several brake applications the fluid level remains the same, measure the wheel turning torque required to rotate the wheels with brakes applied as follows:
Apply the brakes slowly to a minimum of 45 Kgm (441 N) of force and hold for approximately 15 seconds. With the brakes still applied, exert torque on the front wheels to 101 Nm (75 lb/ft). If the wheel can be rotated, the brake master cylinder is bypassing. Repair or replace the brake master cylinder. Refer to Section 206-06 .


Non-Pressure Leaks

The only part of the brake system that could have a brake fluid loss that does not appear when the system is under pressure is the brake master cylinder reservoir area. Brake fluid loss could be caused by a missing or poorly-fitted brake master cylinder filler cap (2162), a punctured or otherwise damaged brake master cylinder reservoir, a missing or damaged brake master cylinder filler cap gasket or by missing, damaged, or poorly-fitted sealing grommets between the brake master cylinder and the brake master cylinder reservoir.

The brake master cylinder reservoir grommets are not separately serviceable and must be replaced as a unit with a new brake master cylinder reservoir.

NOTE: The wet appearance on the outer cover of rubber brake hoses is called "sweating." This is a normal condition for neoprene rayon braid hose. The "sweating" condition is not evidence of a brake fluid leak and will not result in a loss of pressure in the system.

Replace a flexible brake hose if it shows signs of softening, cracking, or other damage.

When installing a new brake hose, position the hose to avoid contact with other vehicle components.



Compensator Port Check

The purpose of the compensator ports in the brake master cylinder is to supply any additional brake fluid required by the system due to brake pad wear and to allow brake fluid returning from the brake lines to the brake master cylinder to enter the brake master cylinder reservoir.

The returning brake fluid will cause a slight turbulence in the brake master cylinder reservoir. Turbulence seen in the brake master cylinder reservoir upon release of the brake pedal is normal and shows that the compensating ports are not plugged.



Proportioning Valve

If there is a brake system concern such as premature rear brake lockup that cannot be attributed to the rear anti-lock brake system (RABS), the cause may be a malfunctioning brake master cylinder fluid control valve (2C161).

Check the brake master cylinder fluid control valve by substituting the suspected bad valve with a known good one. If the condition persists, recheck the RABS; refer to Section 206-09A .

__________________________________________________ _____________

I guess the "rabs" is the proportioning block. The newer models 99+ have a seperate block down on the frame or close to it. Ours just has the one.

 

Thanks Jbrew!
A few things....

Yea the aluminum block you that is attacked by a hard line to the master cylinder. Is there a specific name where I see if parts stores carry it or find it online?

I'm leaking right the lowest part on that block. From factory it had a really long fitting on it, we just used a regular brake line fitting. Not sure why they used such long fitting. Your's looks long too in the pic. I tried posting a pic pointing to the items but I can't post pics. didn't see an option for it.

I"m talking about the line that goes to the rear..it's attached to the lowest part of the proporioning valve.

hopefully I'll be able to find one at a local yard or that they are cheap enouph to pick up at a parts store.

It has a wiring harnes to it on the bottom...figured it was abs related.

Thoughts, suggestions. I know I'm leaking there when you press the brake pedal, not when just sitting there but it does leak good when you press the pedal.

Thanks again for all the help Jbrew.

 

The anti-lock electronic control module (2C018) located in the center of the instrument panel.
RABS valve (dual solenoid electro-hydraulic valve) is located under the brake master cylinder (2140).
The rear brake anti-lock sensor (2B190) and rear brake anti-lock sensor ring are located in the rear differential case (4204).
The yellow ABS warning indicator is located in the instrument cluster.
The RABS diagnostic connector is located in the cab behind the right side cowl side trim panel (02345).
Diode/resistor element located in the wire harness at the windshield washer solvent reservoir.
RABS sensor test connector with cap located in the engine compartment on the bulk head above the brake master cylinder.
The anti-lock electronic control module performs system tests during start-up and normal operation. The RABS valve, rear brake anti-lock sensor, and fluid level circuits are monitored for proper operation. If a concern is found, the anti-lock electronic control module deactivates and the yellow ABS warning indicator illuminates.

Most concerns cause the warning indicator to stay illuminated until the ignition is turned off, at which time the anti-lock electronic control module retains the diagnostic trouble code (DTC) in memory (also referred to as keep alive memory or KAM). At any time while the ignition is turned on, a DTC may be obtained. A special DTC 16 indicates that the system is operating normally. However, those concerns associated with loss of power to the anti-lock electronic control module cause the system to be deactivated and the yellow ABS warning indicator to be illuminated, but do not cause a DTC.

The system diode is actually a diode/resistor element. The diode/resistor element prevents a false DTC 12 from being set when the parking brake is applied.

The brake on/off (BOO) switch, when activated, signals the anti-lock electronic control module that a braking condition is occurring.

The rear anti-lock brake system (RABS) continuously monitors rear wheel speed with a rear brake anti-lock sensor mounted in the rear differential case. When the teeth on the rear brake anti-lock sensor ring, mounted on the ring gear, pass the RABS sensor pole piece, an AC voltage is induced in the sensor circuit with a frequency proportional to the average rear wheel speed. In the event of an impending lockup during braking, at vehicle speeds above approximately 8 kph (5 mph), the anti-lock electronic control module senses the drop in rear wheel speed. If the rate of deceleration is excessive, the anti-lock electronic control module activates the RABS valve, causing the isolation valve to close. With the isolation valve closed, the rear wheel cylinders (2261) are isolated from the brake master cylinder and the rear brake fluid pressure cannot increase. If the rate of deceleration is still excessive, the anti-lock electronic control module will energize the dump solenoid with a series of rapid pulses to bleed the rear wheel cylinder fluid into an accumulator built into the RABS valve. This reduces the rear wheel cylinder brake fluid pressure and allows the wheels (1007) to spin at vehicle speed. The anti-lock electronic control module pulses the dump and isolation solenoids in a manner that will keep the wheels rotating while still maintaining high levels of deceleration during braking.

Once stopped, the operator releases the brake pedal (2455), the isolation valve de-energizes and any fluid in the accumulator returns to the brake master cylinder. Normal brake operation resumes.

 

 

I answered that one

Anything else while I have this opened up?