Brake pedal goes to floor with no resistance first time I start in am. Rest of day all normal. Started when cold weather came. Fluid ok, no leaks seen. Ideas?
More than likely there’s an internal leak in the brake master cylinder. I had the same thing happen with my trucks clutch master cylinder. Pedal to the floor on the first push when the weather got cold.
Get it looked at ASAP and do not continue driving it.
I agree with the other two. If we’re right, eventually that pedal is going to start sinking to the floor with no resistance more often than just when you first start it - quite possibly when you’re in traffic.
If you’re mechanically-inclined, replacing an MC is very easy and will probably cost you less than $100 including new brake fluid (which you might as well do as long as you’ve cracked the system). If you take it to a shop, it might be north of $600, so there’s definite incentive to do the job yourself if you can.