Brakes Hard as a Rock

mwm695

mwm695

New member
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!
 
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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.
 
Try brake booster check valve. Should run you about $35 at the dealer. #44730-60060. #90480-24015 if you want the grommet too.
 
mwm695 said:
Thanks!

Is it an easy fix?
Click to expand...

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.
 
shootmymime said:
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.
Click to expand...
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 :wow:
 
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.
 
ILRunner98 said:
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.
Click to expand...
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.
 
lbhsbz said:
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.
Click to expand...
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?
 
krenaud33 said:
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?
Click to expand...
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 [MENTION=78704]lbhsbz[/MENTION] said above, its just too damn cold haha
 
krenaud33 said:
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?
Click to expand...

Mine does the same thing. It's the vacuum assist issue that's described above. I know two other people who've experienced the exact same issue. Doesn't really matter how long the truck has been running, it's the first couple of pedal applications. If you pump the brakes a couple of times before you get going it will go back to normal.

The scary part is when you forget about it and don't realize it until you're backing out of a parking lot somewhere. :fear:
 
madcanvis said:
x2

This phenomena started with mine last year on days <15*F
Warming up the rig does not help but a couple pumps of the brake pedal does.

Willing to give the WD40 and compressed air clean-out a shot when temps creep up.
Click to expand...
Please let me know how this works :)
 
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