So this has happened 3 times now in very cold conditions (single digits but not everytime). Basically I just start the truck up and the first time I really hit the brakes while moving they are hard as a rock and I have to pump them 2-3 times and they soften up and actually brake the vehicle. Is this an indication of the booster going bad? Perhaps there is condensation on a valve in there that sometimes freeze up said valve? Other than that initial thing it's working totally fine (other than maybe just needing a good solid bleed in general).

Mine will do that from time to time when it's really cold. I don't think anything of it.. ( That might be good or bad)

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Well I think we can rule out rust issues on our problem since I don't have those lol. Yeah it's not been an issue after that initial hard pedal. I probably just need to be mindful on cold days to check the pedal at slow roll until I pull out into the road. First two times it happened was 1/4 mile down the road. Always a little terrifying when you are pulling up to a light and it happens, one time I was behind a school bus. Glad I drive like a grandma for the most part in this truck. Last time it was while I was backing up from my parking spot in the road to get around my roommate. I think possibly first two times I didn't have to back out of my spot. I'll keep an eye on things to see if I can figure this out more but I know I always put my foot on the brake initially to disengage the parking brake and get into gear and I don't have the problem then. Super weird.

A couple of minutes of warm up could help. The check valve might be gummed up.

Yeah I don't think it's ever happened after a good warmup, only when I don't do that. Makes sense that some condensation could be working it's way up from the intake into that vacuum line and freezing the check valve up until I give it enough pedal to unstick it. I guess not really anything that can be done about that which I guess is good and bad. At least it indicates I don't have to buy anything/work on it.

First time it happened. I thought my brakes were frozen and it scared the heck of out me as the brakes didn't work for a few seconds..lol

I’d think about replacing the check valve. It’s done it to me on two separate rigs.


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Sounds like the check valve.
Had the same problem on my 2nd gen and replacing the check valve solved the problem.
Had the problem on my 3rd gen and I sprayed the check valve with silicone lube and that fixed it.

In my case warming it up didn't help at -30.

I will need to investigate that check valve.

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Did you remove the valve and spray into it?

I didn't remove the valve but I removed a hose on one end of the valve and sprayed into it. It's been good for 5 winters since.
I actually used Tri-Flow lube.