Martineze37

In my '94 Honda Accord EX, My brakes required me to push all the way down to get little actual brake power. Eventually they went out completely & entirely to where i push the brake pedal all the way to the floor and now absolutely nothing happens. First thing i did was replace my MC, (though i didnt properly space the booster piston & the MC) after bench bleeding the MC and the brakes, the brake pedal now has pressure when the car is off only. If the car is put in neutral & pushed, the brakes work seemingly fine. As soon as the engine is on, all pressure is lost and the same problem occurs. I checked my lines, to find one was actually cut (lol how scary) and ended up replacing that line, rebleeding the brakes only for the same results. Firm pedal when engine is off, only to lose pressure when the car is on. Extremely desperate for any input. I've found the possibility of the booster being the issue, but if that's the case, wouldn't the pedal be hard when the car is off? Need all the help i can get

MAD_MIKE

Did you use a new MC or did you use a used or rebuilt MC?
Rebuilt units don't have the best track record.
Used unit would be fine if you did not floor the pedal, once that is done, especially on an older/used MC, the piston will travel into the unpolished section of the MC bore and tear the seals.

How did you bench bleed your MC?
MCs usually come with a bleeder kit to easily bench bleed the MC.

Martineze37

It's a brand new MC, and i used the bleeder kit & followed the instructions it came with to bench bleed it.

MAD_MIKE

Doubt it is the booster, it either assists or doesn't.
Is there any notably loss of fluid?
Have a second person watch each hose and see if it balloons when depressing the pedal. There are six hoses in total. It could be one is ballooning only with the aid of booster assist.

Martineze37

All the lines seem to be working fine, especially when the cars off, but as soon as its on they lose all pressure again. After further inspection turns out the computer was unplugged. I plugged them both back in, and the abs light came on. Could this relate to anything or is it from lack of information from the computer? Also tested abs fuses & one of them seems to be faulty.

r_kage

I'll just throw a few things out there that may or may not help:

1) The Accord brake lines need to be bled in a different order than other cars: Rear right, left front, left rear, front right. (I gravity bleed first, and then get a helper to operate the brake pedal while I inspect the fluid. If bubbles keep coming, then air is being introduced somewhere.)

2) Sometimes tiny leaks (which don't result in fluid on the floor) can introduce air into the system. That cage that holds the fuel and brake lines can conceal damage--my own car passed inspection shortly before my brakes failed. My brake lines broke into segments when removing that cage, and there was also a leak to the line that runs over the gas tank. Check the hoses and also check the connections for dampness.

3) When bleeding brakes, make sure there's a block under the brake pedal. If you press the brake pedal too far, you can damage the seal in the master cylinder.

4) This information is from my service manual under BRAKE BOOSTER INSPECTION:

Functional Test
1. With the engine stopped, depress the brake pedal
several times, then depress the pedal hard and hold
that pressure for 15 seconds. If the pedal sinks, the
master cylinder, brake line or a brake caliper is
faulty.
2. Start the engine with the pedal depressed. If the pedal
sinks slightly, the vacuum booster is working. If
the pedal height does not vary, the booster or check
valve is faulty.
Leak Test
1. Depress the brake pedal with the engine running,
then stop the engine. If the pedal height does not
vary while depressed for 30 seconds, the vacuum
booster is OK. If the pedal rises, the booster is faulty.
CAUTION: Do not try to disassemble the booster.
Replace the booster assembly with a hew one.
2. With the engine stopped, depress the brake pedal
several times using normal pressure. When the pedal
is first depressed, it should be low. On consecutive
applications, pedal height should gradually rise.
If the pedal position does not vary, check the booster
check valve.
Check Valve Test
1. Disconnect the brake booster vacuum hose at the
booster.
2. Start the engine and let it idle. There should be vacuum
available. If no vacuum is available, the check
valve is not working correctly.
Replace the check valve and retest.