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1998 Toyota Camry - Air leak between master cylinder and brake booster

There is an air leak and hissing sound at the connection of the master cylinder to the brake booster. Brake pedal travels nearly to the floorboard before engaging the brake. What is the problem and how can I fix it myself? (Special note: the brake fluid was very low and is now topped off to the maximum level . Adding the brake fluid caused very little change to the brake pedal travel.)

You may need to replace the booster. The hydraulic system is independent of the booster system.

Yeah. Air isn’t leaking out of the booster, it’s leaking in. And if you see any indication of brake fluid at the master cylinder/booster joint the master cylinder needs replacing also.

Also, you probably have air in the master cylinder. You could try bleeding it by loosening the brake lines coming out while someone pushes on the brake pedal. If you can’t get a hard pedal that way, you’ve either got a bad master cylinder or air farther down the system.

Yes, the sound you hear is from air leaking through a ruptured diaphragm in the booster and if the fluid in the master cylinder got too low you sucked air into the brake lines and the brakes need bleeding.

Also, there are only two reasons for brake fluid to get low. Either your pads or shoes or both are worn enough to need replacement, or you have a leak.

If you see an unusual amount of smoke coming out the tailpipe, that could mean brake fluid is getting sucked into the intake manifold from the defective brake booster.