Occasional loss of brake boost after being parked

Not sure if this is 'normal' or indicative of a small problem.

 

Usually when returning to the car after it's been parked for several hours, there's a couple of pumps (or is that strokes? whatever ) worth of brake boost vacuum left before the pedal gets hard (ok, this is immature) before turning the engine on again.

 

I've noticed on occasion though that the pedal is firm with no vacuum assist until I start the engine. Is this normal or perhaps a small leak?

 

Cheers.

Your car has a check valve at the brake booster, it is probably leaking.

So tell me why you even check that ?

 

I know I may be old, only been driving for almost 50 years. I didn't know you were supposed to do that when you get in the car prior to starting it.

 

All these years I open the door, get in, put key in slot, push in the clutch, turn key to start.

 

 

I do believe there is something in the owners manual about the brake booster and how to check it... or was that in the Honda Civic manual from about 25 years ago where I read about that...

 

The service manual may have some info,

 

http://people.csail.mit.edu/ilh/vacation/

Also, check the vac line leading to the brake booster from the intake manifold. By now, they're old and begin to crack like all the other vac lines under the hood.

So tell me why you even check that ?

 

I know I may be old, only been driving for almost 50 years. I didn't know you were supposed to do that when you get in the car prior to starting it.

 

All these years I open the door, get in, put key in slot, push in the clutch, turn key to start.

 

 

I do believe there is something in the owners manual about the brake booster and how to check it... or was that in the Honda Civic manual from about 25 years ago where I read about that...

 

The service manual may have some info,

 

http://people.csail.mit.edu/ilh/vacation/

 

The vast majority of modern cars, especially ones with push-button starters, shifters without hard detents (something like a modern BMW shifter), etc, need the brake pedal pushed in to start. Jags with third pedals actually need both the clutch and brake pedal pushed in! You'd notice a lot more in a car with electrically-assisted brakes some problem akin to OP's, but I definitely don't recall ever being able to push my pedal down in my wagon that far before starting the car. Habit, I suppose, from driving new Chevys at work.

Yes our 2018 Outback needs to have the brake pedal pressed so I understand that.

 

I assumed he's talking about a 4th Gen car.

If the diaphragm in your booster has a small tear, you're sucking in un-metered air into the engine and messing up your air fuel ratios. So yeah, it's sort of important.

Hopefully the OP will check back in soon.

 

I agree sounds like a Master Cylinder could have issues. Could be as easy as the check valve too. But I think we know how most things end up going.