1991 4Runner, 3vze, 5spd.
Story:

It was blowing snow, temp around zero, or below. Runner sitting at work.
Went out to go to another building. Started vehicle, took off out of the parking lot. I normally have to brake at exiting the lot. Didn't, because of all the snow, no vehicles coming, etc. Went about a mile or so, THROUGH the next intersection (needed to turn left) as the brake pedal was ROCK HARD. I mean NOTHING. As if a 2x4 was under the pedal. Of course I pumped it a few times. By the time I was 1/2 through the split/double lane intersection it worked fine. No other issues. Was fine the rest of the day. Haven't been out today yet, so I haven't checked fluid level yet. I usually step on the brake at start-up, so a harder pedal for a moment I am used to. I didn't notice anything at the time that caught my attention.

Question: Could something have simply frozen?

Ant comments would be appreciated...

 

I just remembered: I did just have the power steering pressure hose replaced four days ago. One wouldn't think it is related...

 

It is quite possible for water (moisture) to be in the brake fluid. The older the fluid the more moisture is likely to be in it. This is why when brake lines are replaced that it is important to replace all of the fluid!

If you can empty your fluid and then bleed all of your brake lines (starting furtherest from the resrvoir) until you see new fluid you will be able to easily eliminate the this type of freezing (assuming it is minor freezing in the fluid).

 

Flush and replace all brake fluids. Its very, very hydroscopic and probably froze on you. With all that pumping you managed to break up the slush and the engine heat kept it from refreezing.

This has to be done once in a while with DOT 3 fluid. Start from the left rear and work you way around the car bleeding the old fluid out until the new clear fluid shows.

 

Maybe the brake booster froze up. I guess it depends on just how hard that pedal really was, because if it was hard to push but still worked, that sounds like the booster.

 

happened to me once, never happened again after... kinda scary at first lol.

 

Happened to me a number of times the winter before last.
Can't remember exactly what it was but I think it was a one way valve on the brake booster vacuum line that was freezing up.

 

If you have the rear ABS, the power steering is involved in the brake system:
- http://www.autoshop101.com/forms/brake09.pdf

 

When brake fluid gets old it degrades and attracts moisture. Water freezes at 32* fahrenheit. Flush the brake fluid and it shouldn't happen again.
And flush again ever 30K miles.

 

Went and checked.
It was the Vacuum Check Valve that's inline on the large vacuum hose going to the booster.

Brakes feel rock hard because the booster isn't getting any vacuum for a bit just like if you tried to use them with the engine off.

 

I'll 100% agree on flushing the fluid and refilling with new fluid

brake fluid is actually DESIGNED to absorb moister in a brake system (it traps the moister so that the brake system doesn't fail - water compresses and would make the brakes become less responsive or "spongy"; brake fluid which is basically hydraulic fluid doesn't so much); that's why you never use an old bottle of brake fluid that's been opened in the past and has sat around for a few months. water trapped in the system is obviously going to freeze in freezing temps, so that's why the system will lock up

I would even go as far to say it's the original fluid in the truck unless YOU have even flushed it yourself

 

THIS. My celica does it. My subarus have done it. My 4runner has done it. that valve is extremely easy to replace, and usually pretty cheap to replace(I know the subaru one is inserted in the hose, so they sell you the whole hose. and it's like $8). But usually, you can take it off and bring it inside for awhile to make sure it gets good and dried out, and it'll clear up.



Or, just know that it can stick, and test the brakes before you start rolling on cold days.

 

Thanks for the replies.

The brake fluid should have been new two years ago, as I had a break in the line (go figure, at a dealer no less). So they fixed the line.

I was out today, no problems. I will have the system (fluid/booster/valve) checked.

Thanks again!

 

My brake booster used to not work from time to time, causing the brake pedal to go hard. But ever since I ran Seafoam through the engine, by way of the brake booster hose that goes to the throttle body, it hasn't done it once.

I'm thinking that the Seafoam must have helped clear the brake booster valve for me.

 

I have the same problem with my brakes they stiff and when I press on the pedal iis rock hard and makes a squeecky sound but the only difference is that I live on Vegas and is 112 degrees out today.