I've had this problem for the last 2 years or so and I'd finally like to address it. When it's cold out (below freezing) after first starting the car the slightest tap of the break will cause the tires to lock. This persists until I pump the pedal a few times and it's more or less fine the rest of the journey. Also when it's raining or the roads are snow covered after driving a few miles without using the brakes they don't seem to work as they should. I'll hit the pedal and the car will slow but much less so than would be normal. It's as if the pads are maybe slipping, but standing on the pedal doesn't seem to help any either.

Suggestions where I could start looking?

Oh, and I do have enough brake fluid

EDIT: I'd like to add that in situation A the pedal is VERY stiff and I have to really press on it to pump it back down to a normal level. In situation B the pedal is VERY soft and I have to pump it back up to a normal level.

 

If it were me, I'd start looking at the power brake booster.

 

Thanks for the tip, is there a way to check if it's working correctly without just replacing it and hoping for the best?

 

Clean the dust out of your rear drum brakes. On newer cars there is no way for it to escape, it just accumulates inside. However that causes brake lockup in wet conditions more than freezing. And yes Dcotter is correct about the brake booster. There could be humidity trapped inside and freezing.

 

Tests for the brake booster occupy about 3/4 of a page of the shop manual, all text. I'm not about to type it out here. Basically, they involve conducting various vacuum tests. Maybe if someone has an electronic version of the manual he can copy and paste it for you.

If you can rule out the other areas of the system such as recommended by TNtech, then the booster is likely the source of the problem. There are no repairs recommended for the booster. If it's bad, you replace it.

 

I have rear disc brakes on the car so it's not a build of up brake dust. Also I was able to find a few "how-to" instructions online (thanks Google). Thanks a lot!

 

Let us know how it all works out.

 

It looks like the rear brake calipers/piston is stuck. It stays OPEN and freezes in that position probably, hence the stick brakes, until it warms up, and then it retracts. Try to replace the caliper and new brak pads, that should fix the problem. I would replace the rotor too and bleed a lot of old fliud out to get any rust or junk out! Also pull on the brake cables when pads out to check for hand brake cable bind.
Good Luck