Rakes are "soft", go to the floor

MATHIEU369

MEMBER
1990 HONDA ACCORD
4 CYL
2WD
AUTOMATIC
138,521 MILES

Brakes are "soft", go to the floor. Pumping does not help much. Sometimes it works OK for a few minutes then goes back to soft again. Reservoir is full of fluid. Should I bleed first or do I just replace the Master cylinder?

Wednesday, January 14th, 2009 AT 8:12 PM

1 Reply

DAVE H

MECHANIC
13,383 POSTS

TESTING
POWER BRAKE UNIT TEST
Functional Test
Start engine. Turn ignition off. Depress brake pedal several times. Depress pedal hard and hold pressure for 15 seconds. If pedal sinks, master cylinder, brake line or wheel cylinder is faulty.
Start engine with pedal depressed. If pedal sinks slightly, vacuum unit is working properly. If pedal height does not vary, booster or check valve is faulty.
Leak Test
Depress brake pedal with engine running. Turn ignition off. If pedal height does not change while depressed for 30 seconds, vacuum booster is okay. If pedal rises, vacuum booster is faulty.
With engine stopped, depress brake pedal several times using normal pressure. Pedal should be low when first depressed. On consecutive applications, pedal height should gradually rise. If pedal height does not vary, check power brake booster check valve.
Check Valve Test
Disconnect power brake unit vacuum hose at booster. Start engine and allow engine to idle. Ensure vacuum is available at booster end of hose. If vacuum is not available, vacuum source or check valve is faulty. Repair vacuum source or replace check valve and retest.