for your brakes to work? I am not trying to drive with the caps off, but my old caps lost their gaskets and I was trying to do a quick test drive around the block to check out the effects of my clutch and brake line flushing. I completely gutted the gaskets and put the caps back on. When I pushed the brake pedal, it went to the floor (while the engine is running).

Caps have no effect on brake function. You've got air in the lines, or an open bleeder.

Can't be an open bleeder, checked around the floor. I am almost 100% certain there is not air in the lines.

I'll keep checking.

Update. I have brakes, though the pedal feel is soft. It feels like air in the lines, but I triple checked before disconnecting the bleeder.

Could the master cylinder have air?

The caps would keep the proper pressure for the hydraulics to work correctly. I know I am stating the obvious, but the vehicle was built to have the caps on there for optimum performance.

The caps keep the brake fluid clean by not allowing dirt and moisture from the air to get in the system, and keep the brake fluid off the paint in enthusiastic driving! The caps are actually effectively one way vented to keep a vacuum from forming as the pads wear and the fluid level drops in the MC. In the very short term, the presence or abscence of caps has no effect on the brake system, but I would keep the system capped, and bleed it if it went un capped for any length of time(depending on humidity and brake fluid used)

Will

To answer the master cylinder needing bleeding: Beandip came over and did my brakes, and we were having problems bleeding the system out. Pedal went to the floor, it wasn't until he bled the master cylinder and THEN the calipers that he was able to declare them bled out.

FWIW

E