Please help me debug a hard brake issue.....

[NM_Shooter]

Very cold this morning. Went out to drive my 97 T4R LTD, and the brake pedal was hard as a rock and the brakes almost unresponsive.

Pumping the brake a little loosened it up, and within seconds it was operating normally.

Doing some research I have three things to try, and I'd like your opinion and help.

1) Sounds as though it could be the check valve on the vacuum booster. What the heck is this, and how do I find it?

2) My brake fluid is old, and may have moisture in it. I am going to flush it with new DOT4.

3) My master cylinder / vacuum boost is shot.

Any and all thoughts / suggestions / help welcome! Thanks!

 

[NachoPitt]

Could also be air in your brake system - a good bleeding of the system after a flush would help.

 

[nevada]

the check valve is toward the top, and to the left on booster. it will have large vacuum hose going to it. pretty hard to miss.

you may or may not need the fluid flushed, but that wont give you a hard pedal.
neither will air in the system.

 

[Qyota]

100% it's the check valve. $26 part. 1 minute to replace.

 

[Buckaroo]

Have had this same issue. Interested to know the outcome.

So the check valve fails when very cold allowing the vacuum to leak off the backside of the booster? My experience is that the peddle is so hard that it feels like something other than just lack of power assist.

 

[Qyota]

Valve sticks, not allowing vacuum to the booster at all. Very common issue, and the fact that it happens in a cold snap pretty much gives it away. Just change it, trust me! ;-)

 

[RussToy]

I had this problem just after I bought my 4Runner...it was freezing out also. Mine was the check valve...I think it was like $20-25 to fix. Took all of a couple minutes to replace.

I had 150,xxx miles...so I went ahead and flushed my brake system with Amsoil brake fluid...just to give me a warm and fuzzy feeling!

Good luck...