Car: 2001 Forester L On super cold mornings, I'm having some issues with the brake pedal feeling super rock hard and brakes not working for a bit until it warms up a bit. I've read online that it might be a check valve or a bad booster. Is what I'm seeing a brake booster failure? They seem good the rest of the time and on warmer days. Also, I did upgrade the front brakes to a set from a 2013 WRX. Could this have caused this issue? Lastly, should I upgrade the brake booster and if so, what is compatible? I'm assuming a 2002-2007 WRX booster would be compatible.
I'm having this exact same issue on an '03 WRX. They still work solidly, but the pedal feels super stiff until the car warms up. I know I'm due for a fluid flush/change, but not sure if that's the main cause or not.
I just had the brake lines flushed when we redid the front calipers. I don't think the fluid is the problem.
Are you sure that it's not just the cold? My everything boosters has been stiff over the past few weeks. Brake pedal hard, shifter stiff as can be...i let everything warm up for about 10-12 minutes and all is well.
I'm not sure of anything, that's why I'm asking. One post talks about a check valve getting moisture on it and freezing. Could be due to cracked/worn hoses right under the vents between hood and glass. Even if it's just cold, I'm still wondering if I should swap the booster out for a different one to handle the new brakes.
That's kinda what I was hoping. I warmed mine up for 15+ today and it still wasn't at normal operating temp when I left. Frickin' cold out there this morning!
There's a check valve in the vacuum line that goes from the intake manifold to the booster. Over time, you can get a little moisture residue on there, and it will freeze shut in the brutal cold, thereby giving you zero, or very limited, brake booster. You can either replace it (have to buy the whole line), or just clean it. You need to clean it with something that doesn't leave a residue. My favorite is MAF sensor cleaner. Pull the hose off from the booster side, start the car (it will probably run rough with the post-MAF leak), and then shoot short bursts of MAF cleaner in there. The engine will draw it through the check valve, and probably solve your issue. I think I've done this on every vehicle I currently own with success.
My money is on this. Had similar issue with a Toyota. That said, this Toyota and the Outback we gave to my step-daughter were the only cars I have taken care of that had this problem - none of the domestics ever did this.
