Recently I've noticed that I have no vacuum left in my brake booster when I go to start my truck after a few hours or more. For those of you with push button start and have to depress the brake pedal to start the truck, have you noticed that the pedal is extremely firm after an overnight set? If I go back to my truck within an hour or two, I have my usual soft pedal. If I wait longer than that, it's so firm that half the time my truck doesn't start as the pedal isn't down far enough. It wasn't this way on delivery and would be the same after an hour or sitting for days. I've got an appointment to bring it in next week but wanted to see if anyone else had this happen?

 

Can't help since I have the wrong type of brakes. But, I wonder if the vacuum system is tied in with the 4WD hubs? Perhaps one of them is already slightly leaking?

 

That's a possibility and I wondered about if they were connected. This happened once before after engaging 4x4 and it went away after the next use. I have since tried engaging 4x4 to see if it stopped, which didn't work. Good thoughts though T. I'll mention that when it goes in.

 

Component Test-Brake Booster-Vacuum Boost

NOTE: If oil contamination is found and the vacuum system is not replaced during brake booster replacement, booster failure will occur again.

If equipped with a diesel engine, inspect the brake booster, vacuum lines and check valve for signs of oil.

If oil is found in the vacuum line(s) or check valve, replace the brake booster, all vacuum lines, vacuum reservoir and the vacuum pump at the same time.

Disconnect the check valve from the brake booster and connect a suitable vacuum/pressure tester to the check valve.

Apply the parking brake, start the engine and place the transmission in NEUTRAL.

Allow the engine to reach normal operating temperature.

NOTE: Subtract approximately 3.38 kPa (1 in-Hg) from the specified reading for every 304.8 m (1,000 ft) of elevation above sea level.

Verify that vacuum is available at the vacuum sensor/check valve with engine running at normal idle speed.

The vacuum gauge should read between 51-74 kPa (15-22 in-Hg) on vehicles not equipped with a vacuum pump and 70-85 kPa (20-25 in-Hg) on vacuum pump-equipped vehicles.

If specified vacuum is available, stop the engine, connect the check valve and continue with Step 6.

If specified vacuum is not available, continue with Step 5.

Disconnect the vacuum sensor/check valve from the vacuum hose and verify that the specified vacuum is available at the hose with the engine at idle speed and the transmission in NEUTRAL.

If specified vacuum is available, stop the engine, install a new check valve and check the system for normal operation.

If specified vacuum is not available on gasoline engine vehicles, stop the engine, connect the vacuum hose to the check valve and diagnose the no/low vacuum condition.
REFER to: Engine (303-00 Engine System - General Information, Diagnosis and Testing).


If specified vacuum is not available on diesel engine vehicles, inspect the vacuum hose and install new as necessary. If vacuum hose is ok, install a new vacuum pump.
REFER to: Brake Vacuum Pump (206-07 Power Brake Actuation, Removal and Installation).


Apply the brake pedal several times to exhaust all vacuum from the system.

Apply the brake pedal and hold it in the applied position. Start the engine and verify that the brake pedal moves downward after the engine starts.

If the brake pedal moves, the brake booster is operating correctly.

If the brake pedal does not move, install a new brake booster.
REFER to: Brake Booster (206-07 Power Brake Actuation, Removal and Installation).


Operate the engine a minimum of 20 seconds at idle. Stop the engine and let the vehicle stand for 10 minutes, then apply the brake pedal. The brake pedal feel should be the same as that noted with the engine operating.

If the brake pedal feels hard (no power assist), install a new brake booster vacuum sensor/check valve and retest.

If condition still exists, install a new brake booster.
REFER to: Brake Booster (206-07 Power Brake Actuation, Removal and Installation).


If the brake pedal feels the same as noted with the engine operating, the check valve is functioning properly.

 

Great info! Was this a TSB for a known issue?

 

Ford shop manual trouble shooting guide for hard pedal

 

Thanks much. Reps sent.

 

Mine is exactly like what you described Rodney, been that way since day 1 and I didn't think much of it. It has never not started due to the firmness or anything like that though.

 

Oh, it will start but it shouldn't be that hard Andy. It should be a nice soft pedal when you depress to start the truck. If it's rock hard, there is a vacuum leak. Either a check valve or the booster itself. Somewhere it's bleeding off when your not running.

 

Great info wb6anp (callsign I pressume). Would you happen to know if the ESOF 4X4 vacuum is integrated with the brake boost system or are the 2 systems stand alone?

On my '02 the 4X4 hubs are isolated from the reservoir by the Pulse Vacuum Hublock which of course controls vacuum to the hubs. I am interested to see if this technology has changed much since then.

 

I've had my truck since late January. I've had this happen 6-8 times over the past couple of months. Haven't thought a lot about it, but will mention it to the service department next time I go in.

 

Mine was coming and going since delivery little over a month ago. Now it's there at every start up with anything more than an hour or so soak.

 

The electronic shift 4WD system consists of the following:

Transfer case
TCCM
High Speed Controller Area Network (HS-CAN)
Mode Select Switch (MSS)
Transfer case shift motor
4WD indicators and 4WD system messages in the IPC message center
Constant Vacuum Hublock (CVH)
CVH solenoid and vacuum lines
Vacuum pump (diesel engine only)

The ESOF uses CVHs to engage the front axles. The CVHs are automatically controlled by the TCCM using the hublock vacuum solenoid, which either applies vacuum to the CVHs (4H or 4L) or releases and withholds vacuum to the CVHs (2H). Diesel engine vehicles are equipped with a gear-driven vacuum pump that is mounted to the front of the engine behind the accessory drive cooling fan driver and is serviced as an assembly.

Bought the factory manual cd off the Helm site for $177.00, the wiring diagrams are hard copy and seperate.

 

I am taking it in for the first oil change at 5k and also to have the transmission FSA fixed and will mention this.

 

Rodney/Andy/anyone else have any updates on this? Thanks.