"Hard" brakes before start

[thefranchise713]

For starters, I'll just say that the brakes have been checked by the dealer--all checked OK.

Every so often, I will go into the car and it will have lost all of it's vacuum from the brakes--when I start to push the pedal down to start, hard as a rock. Vacuum immediately comes back without an issue when the engine runs. Other times, it holds the vacuum perfectly until the next key cycle--pedal goes down normally even before key start.

I am careful not to touch the brakes after key-off to maintain system vacuum. I have never lost vacuum while driving, either.

Any thoughts?

 

[Exit32]

Typically, there's a check valve in the power-boost system that serves to maintain vacuum after the engine has been turned off. Sounds like your Explorer's check valve is leaking intermittently.

 

[omar302]

I'd say it is most probably the brake booster starting to leak. Though not common on the Explorer, it is very common on the Edge. Keep an eye on it, if it becomes more apparent (hold vacuum for less time) the booster might fail while driving & you might get a hard pedal during sudden emergency brakes.

How many days/hours would you keep the vehicle off before getting the hard pedal? If it is a few days, then it is probably normal.

 

[thefranchise713]

It has no consistency, but when it does happen it can be as little as a couple hours or overnight.

 

[613GT500]

If the engine is off, isn't this "hard" brake pedal feedback normal; especially if you continue to step on it.

 

[MikB]

Vacuum boosters don't 'intermittently' leak. They either leak or they don't. Check valves, on the other hand...

It would cost next to nothing to replace the check valve but, check the vacuum line and related connections to insure the integrity of the whole system.

 

[peterk9]

If the engine is off, isn't this "hard" brake pedal feedback normal; especially if you continue to step on it.

Paid attention to that this morning. Upon starting the pedal went about half way down upon my estimation. After starting and pumping it several times, there was no change.

Peter

 

[Odrapnew]

If the engine is off, isn't this "hard" brake pedal feedback normal; especially if you continue to step on it.

If the system is working properly(sealed up tight), you should have some residual vacuum in the brake booster for some time after the engine is shut down.
There's not set limit for how long it will hold vacuum, but I know when I get into my Ex in the morning after sitting overnight, it will still have some vacuum assist before I start it.
If I pump the pedal more than 1 time, it goes away pretty quick.

 

[Dirty D]

Vacuum boosters don't 'intermittently' leak. They either leak or they don't. Check valves, on the other hand...

It would cost next to nothing to replace the check valve but, check the vacuum line and related connections to insure the integrity of the whole system.

I am having the same issue now and running rough at idle while in gear. I have checked most of the vacuum lines visually and don't see anything jumping out at me so I am wondering if it could be the check valve as you suggest. Can you tell me where it's located? I want to check the vacuum pressure and the valve. Thanks!