Hi guys,

Sometimes, when I first start up my truck after a really cold night, my brakes are as hard as a rock. It takes A LOT to stop my truck but only for about 30 seconds.

Could this be a bad brake booster? It doesn't happen all the time, just randomly, then it goes away and the brakes behave normally after that.

Any suggestions?

Thanks!

Yep sounds like a bad booster. Mine had the same issues when i got it rock hard brake pedal and hard to stop. New booster fixed it.

Do you remember how much that cost?

Try brake booster check valve. Should run you about $35 at the dealer. #44730-60060. #90480-24015 if you want the grommet too.

Thanks!

Is it an easy fix?

super easy, its literally a 10 mm bolt comes off then the check valve comes right out after some moving back and forth. it has some barbs on it that will prevent it from wanting to pull out but it will come out.

My check valve does it as well sometimes and i just am cheep and dont want to buy a new one so i just spray some WD40 in it and get the water out that freezes it closed.

Great!

is there a picture of what a "bad" check valve looks like?

They dont really go bad. They collect crud in the valve and at night in the winter, ice forms on the valve locking it closed. I pulled mine out, flushed it thoroughly with WD40 and re-installed it. No problems for the past 3 years now. $40 bucks is insane for that little part.

thanks guys, I'll have to find me a metric socket wrench set out here in the styx for pennsylvania lol

I had the same exact problem a few weeks ago. Cleaned out the vacuum check valve and fixed the issue. Its one 12mm nut that holds on the master cylinder that also holds a little bracket holding the check valve. Spray wd 40 in there and blow air through the valve from the back side about 10 to 15 times to clean it out really good.

Perfect, thanks.

I guess in the time being, i'll just pump my brakes a couple times before I start moving.

This may be normal...don't go changing anything just yet.

How cold are we talking? Vacuum boosters need (obviously) vacuum to work...about 18"hg is the bare minimum. Vacuum is created because the throttle plate is restricting the engine from sucking in all the air it wants. at a cold start, or a real cold start, you're gonna be on a higher than normal fast idle for a bit and ring seal won't be the greatest at sub zero temps. Less efficient pumping action + less restriction against airflow (idle air bypass valve wide open)= low vacuum.

This is a problem for many vehicles...Mercedes has added auxillary pumps to a few of their vehicles....just let it warm up a bit...nothing works well when it's that cold.

Put a vacuum gauge on it and measure manifold vacuum on a cold start to confirm.

Not terribly cold, roughly 20 degrees or so

Same thing happens to my 4Runner even after I let it warm up to idle. I am wondering if I have an air pocket in my line somewhere. Any thoughts on how/why the brake fluid might freeze?

Well, the typical freezing point of brake fluid is -40F, so that's not likely. You probably have dirt/moisture/air in your lines, or like @lbhsbz said above, its just too damn cold haha