I have had this problem in the winters for 2 years. I don't think it happens in the summer at all. Every once in a while when the truck is cold (if it sits outside on a really cold night), the brakes are very hard, and don't stop the truck. For example, yesterday I was backing out of the drive way and mashed the brakes all the way down and there was almost nothing. They were hard right away, but no stopping going on. I kept pumping them as I was backing up and then they seemed to catch. No problems after that.

I just installed new rotors, pads, shoes and drums. What gives? New master cylinder?

thanks

Oh yeah, 2000 4Runner Limited 4x4

Maybe there's air in the line? did you try bleeding them?

Id try bleeding them then id start looking at the callipers then the MC.

what is wrong if only front brakes would lock up? to fix it, rig was running on 1st gear, pressed the brake hard to go back to normal breaking. rig was parked for a day or driving for 30 mins. w/out braking when this happened. 4 corners were bled but not the brake mc.

well, for nasdaqer...did you bleed your brake system when you changed everything? i think that your calipers are just to cold to start moving untill you pump it a few times, then they finnaly catch...id say either: your brakes are just being broken in..or...you have air in your lines...possibly from when you changed everything..or, your master cylinder might be going...but i think that is unlikely, but just for saftey, check for leakage around your MC, like a cracked/blown gasket ect...

I had a Honda Civic that acted like that years ago. I think it was moisture in the hose that connects the power brake booster to the manifold for vacuum. There is a check valve in the hose and it would stick when cold. I changed out the whole hose assembly and had no further problems.

I'd suspect something w/ the vacuum line going into the booster, like it's freezing up or something. If it were the master cylinder leaking, I think the pedal would go to the floor. You could also perform the brake booster test to make sure your booster is airtight.

When I bought new tires a week ago, I had them bleed the system. I was pretty sure that this would help, but it seems it didn't solve it. Anyway to confirm that they actually did it?

If they did actually bleed them, then next stop should be new MC?

If the pedal is hard and not spongy then it doesn't sound like a master cylinder. Could be the ABS accumulator isn't charging fast enough in the cold. Does it happen right after you start the car? IE start it and immediately go and brake?

They would have bled the brakes if the fluid is nice and clean. You can check it.