Hello group, I have a 2009 G-37 coupe. After the car sits for awhile (especially in the morning after sitting all night) the brake pedal needs an extra hard push to activate the switch so the start push button can work. It feels like the brake booster hasn't released the vacuum stored in it. After the car starts I have no issue with the brakes. If the car is off for just a short time there is no problem either. Does anyone know anything about this? Thanks, Corky

 

Sounds like the vacuum in the booster is slowly leaking overnight. I would start by replacing the check-valve.

 

Same car ('09 G37) and exact same issue. Brakes seem fine when engine is on. But overnight, brake petal is hard to push and then softens immediately once engine is started. I want to start by swapping the check valve, but can't find the part, only the part for the full booster ($$$). @corkyboy, what did you have to do to fix? Anyone know if the brake booster check valve is integrated into the booster and not replaceable or is it an easy fix? Thanks all.

 

Did you ever figure out the issue with hard brake pedal after the car sits overnight? I replaced the section of the vacuum hose to the brake booster (with the check valve in it) but it didnt make a difference in my case. Any ideas on how to fix this issue? After starting the car the brake pedal gets softer and feels normal.

 

No, I have not found a solution yet but haven't replaced anything yet. It doesn't seem to affect braking or the power assist when the car is running. I've pumped the brakes multiple times and it keeps pressure. It's just when it sits overnight the brake pedal gets hard as a rock to the point where I have to stand on it to bypass the start safety switch. Once started, pressure builds back up and it goes back to normal. Hoping someone can come up with a solution.

 

If, after sitting overnight, the brake pedal is very hard to press down, then either the check valve is slowly leaking or there is a internal failure within the booster itself. Once the engine is shut off, the booster is supposed to hold reserve vacuum pressure. If this reserve is being vented to atmosphere a hard pedal at startup is the result. The check valve is embedded into the vacuum hose that goes from the engine to the brake booster. There is a o-ring that seals the valve to the inner wall of the hose.

To replace the valve, Infiniti requires you to buy a whole new section of hose, p/n:47474-JK62E for ≈$75. ConceptZ has a individual check valve that you can install for ≈$10. I imagine there are other alternative for those inclined.

If, after replacing the valve, hoses, grommets the pedal still gets hard to press overnight, then there is a internal fault and the booster will have to be replaced.