I got back from a trip yesterday and started my 98 Yukon after 4 days of not driving it. It started fine, but when I tried to use the brakes the dang pedal sank to the floor and the brake light came on the dash for a second.
I got it home and this morning inspected and bled the brakes. Its better, but still not right at all.
The master cylinder is only about a year old. I don't see any leaks.
What could cause this?