Is this normal operation for the vacuum reserve brakes?

[Genesiswonderer]

Okay, so title. I have noticed some interesting things about the vacuum reserve in my 2015 3.8 sedan. So usually it's fine (because you have to hit the brake every time you start the vehicle). But sometimes, the brake pedal will be hard when I go to start the vehicle. This is usually if a. it's random sometimes, maybe because it's been colder lately, or b. the vehicle has been sitting for more than a couple of days.
Other than that, I don't notice any problems with the pedal afaik when driving, it just seems to sometimes get stiff when starting when the vehicle sits for a while, then obviously goes back to normal once the engine fires up.
So, is this normal operation? Or is it supposed to hold that vacuum reserve forever and somethings screwed up?

 

[limitwheel]

I have a 2016 3.8 sedan and have experienced the same issue. The brake pedal will be hard intermittently regardless of temperature conditions. There is no vacuum leak in the hose so I added a vacuum check valve to the booster line to no avail, so I left it in. It's probably a tiny leak in the booster diaphragm. It's something I did notice, otherwise the brake pedal feel normal. You can still press the brake pedal to start the vehicle.

 

[joegr]

I wouldn't say that it is normal, the design is for vacuum to remain for a month or more. However, I would say that it is pretty much usual and expected as the car ages. You can replace any and all check valves and any hoses between them and the booster, but it is more likely to be the valve inside the booster or one of the seals there. (It could be the diaphragm itself, but that is least likely.) You can replace the booster, but rarely is that done since a tiny leak does not alter the operation or safety of the brakes.

 

[EdP]

Okay, so title. I have noticed some interesting things about the vacuum reserve in my 2015 3.8 sedan. So usually it's fine (because you have to hit the brake every time you start the vehicle). But sometimes, the brake pedal will be hard when I go to start the vehicle. This is usually if a. it's random sometimes, maybe because it's been colder lately, or b. the vehicle has been sitting for more than a couple of days.
Other than that, I don't notice any problems with the pedal afaik when driving, it just seems to sometimes get stiff when starting when the vehicle sits for a while, then obviously goes back to normal once the engine fires up.
So, is this normal operation? Or is it supposed to hold that vacuum reserve forever and somethings screwed up?

Could be wear or dirt in the check valve or whatever is used. I had it happen for a few days and then never again. Probably a piece of dirt that finally dislodged. The idea is for it to hold vacuum forever but over time, things do wear. I'd not do anything as long as the brakes are working properly until it becomes really annoying.