Very hard brake pedal after car sits for a while

[Zathras]

When I go to start the car and depress the brake pedal (it's an automatic), it's rock hard. Google tells me this probably means I have a leaking vacuum brake booster or some such thing. This is something that used to happen if the car sat for a week or two, now it's doing it even if the car just sits for a couple of hours. Once the engine is started, the brakes feel pretty normal.

It's not really a significant problem, is this something that really needs to be fixed (for safety or mechanical reasons) or can I just keep driving it like this indefinitely? Thanks for any feedback...

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[sk47]

Hello; First let me repeat a story told on here before. I did some mechanic work on the side. Had one Guy who allowed his Porsche to sit for months to years. When it would not start I would get a call. One time after getting it running again I noticed one of the chambers of the brake fluid reservoir was empty. Car only had front brakes. No rear brakes at all. Owner wanted me to let it go and to drive with front brakes only. In the end I had to tell him I would not work on his cars anymore if the brakes were not fixed. Too much liability on me if he had a bad wreck.
Sure, front brakes do 75 percent or so of the braking so he could get away with such. But the seals which work the front brakes were as old as the seals which failed for the rear and had sat just as long. He balked at the cost of a new master cylinder and only ordered a seal kit. I had him order a proper sized cylinder hone as well. I fixed the brakes and even got him to buy some braided brake lines.

To your question. Sure, you can get away with driving the car as is for who knows how long. Eventually the power brake vacuum booster will fail. (not hold vacuum at all). Then you should still have manual brakes unless Ford has modified the system from what I have known about for decades. You will wind up with manual brakes in effect.
The power the vacuum booster had provided will come from your leg. Will become a good workout for the leg. Stops could become longer.

To me playing around with a braking system is a sort of Russian Roulette. Brakes are like a boat trailer. A top priority. No fun if the engine does not run or the boat has a hole in it, but bad brakes or a bad trailer is much worse.

Here is a suggestion. Check the hose which runs from the intake to the vacuum booster for cracks or splits where the hose fits into the big can.

Good luck and give yourself some extra braking distance.

 

[Snellemin]

Yea, I would get the brakes looked at. Sounds like a vacuum leak.

In the meantime, use engine braking(downshifting) as well. And on the extreme side, you can also use the handbrake on top of that.

 

[sk47]

you can also use the handbrake on top of that.

Hello; question, I looked at a 2026 Mustang back in January. Had an electronic parking brake. Not the manual sort. what happens if such is used to stop a moving car? I can modulate a manual handbrake.

 

[Snellemin]

Hello; question, I looked at a 2026 Mustang back in January. Had an electronic parking brake. Not the manual sort. what happens if such is used to stop a moving car? I can modulate a manual handbrake.

Yea, I'm not a fan of the electronic parking brake nonsense for any sports car. You can't modulate it like a manual handbrake. I'm old school in that aspect.
The Electronic parking brake system lets you have even braking power without any effort, for those with wimpy arms. I believe the EPB uses the car stability control as well for the "electronic drift brake", which you can modulate. Without that feature it's just an on off parking brake.

 

[tomservo92]

There is a check valve where the hose from the manifold connects to the booster. If it's stuck open, the booster will leak down. Verify it's working.

 

[Zathras]

Thanks for the info and feedback. I've had partial brake failures on other cars while driving, and it's a bad feeling...

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