Originally Posted by estimac
We have a '94 F150, manual transmission. About a month ago, it got really cold outside, & the truck had been sitting for a few days. I go to drive it, & the brakes are "stuck" (like the parking brake was stuck). I quickly realize that the brake pedal never returned to its normal position, so I lift it with my foot.
Can you provide more details???
When you got in the truck, was the brake pedal already down and the brakes applied? Or not until you pushed on it? How far down was the pedal? If you push on the brake pedal when this happens, does it return part way but not all the way? Or does it just sit right at the position you push it to?
Something in the system must be adding higher amounts of friction in the cold temperature. The culprits are either the MC, Booster, or Pedal.
The master cylinder is probably fine... all the sliding parts are in the brake fluid so they are lubricated. The booster could be the culprit as it has some seals and other parts that slide and are open to the air. But the boosters are tested at -40 in development so something must have changed to cause the problem. The pedal could also be the issue if it is sticking in the cold temps. That might be the easiest thing to try first... spray the pedal joints with some silicone and see if it fixes it.
DO NOT spray lubricant into the booster (meaning the hole where the pedal rod goes in, or anywhere else). The boosters use EPDM rubber since it is compatible with brake fluid, but it does not play nice with other types of oil and spraying the wrong thing in there could cause major issues.
If the silicone on the pedal joints doesn't do it, you should probably have the booster changed out.