Short story: I can get good pedal in 1-3 pumps, keeps pressure with pedal pushed and has good stopping power. If I release the pedal, within a second the pressure is gone and it will go straight to the floor. Have to pump every time I want to stop, so unsafe to drive.

Long version:
Bought my 94 Accord EX a few days ago. Seller said the right front caliper was bad and needed replacing. The brakes were working at the time, but grabbed and made grinding noises.

I replaced both front calipers and bled the lines. Result, very little pedal and gone in a second. Bled several times, no change.

Next was new master cylinder. Bench bled per instructions, bled all 4 brakes. Got a little better pedal on pumping, but gone in a second.

Noticed ABS reservoir low, so I filled it and spent a night bleeding it and the brakes repeatedly. The bleed valve leaked a few bubbles so I replaced that. No change in brakes. Then I bought new synthetic fluid, emptied both tanks, flushed, filled and bled entire system. Tiny increase in pedal, but still wouldn't hold it.

Today I replaced the front pads and bled again. Better pumping and pedal, still gone in a second. Then I found both rear brakes were seized and rusted. Fixed them, lubed well and bled all the lines again. Now I can get enough pedal in 1 or 2 pumps, still a little spongy but all the stopping power I need. But let go for a second and it's gone. Pedal goes to the floor. Must be repumped every time I want to stop.

What would cause this to lose pressure so fast, after pumping up plenty? I've checked for leaks, secured all lines and fittings, done the repairs, followed instructions. Is there something I'm missing? More bad parts? Black cloud over my head?

Thanks in advance for any advice, including shooting the car.

 

Where did you get the master cylinder? An aftermarket master cylinder may be bad out of the box. How are you going about bleeding the lines?

A bulge in one of the rubber part of the brake lines can cause this.

There are adjustments to the push-rod and brake pedal height that may need to be done.

 

Master cylinder came from Auto Zone. It does pump, but I guess there's no way to prove how good the seals are without replacing it again.

I've bled it with someone operating the pedal while I loose and tighten the fitting, by myself with the tubing under the level of fluid in a large bottle and with those small self-bleeding units. When doing the whole system, I start under the hood and then do each wheel in order, right to left, back to front, constantly checking and filling the reservoir as I go. Once the bubbles are gone I've always done a few more times just to make sure.

Thanks for the response and advice. I'll check those hoses for bulges and cracks. After all this, maybe I should return the MC for a new one too.

 

Update: I replaced the master cylinder again, bench bled it, new vacuum line to booster, check valve is ok, checked hoses & lines and bled the crap out of all for lines and the ABS unit. Push rod and brake pedal seem to be fine as well.

Same outcome... pumps up plenty of pedal, though a little mushy, in 1-3 pumps. Stops fine as long as pedal is pressed. Let go for a second or more and the pressure is gone, pedal goes to the floor. Must start again with pumping every time I need to stop.

HELP!!!!!?

 

With you description, there has to be air in your system. The other alternative is a leak somewhere in your hydraulic system. The master cylinder should to be ok, since you replaced it twice and still get the same outcome.

How did you fix the rear calipers?

Unless everything is new, my best suggestion is to replace the bleeders the rear calipers. Replace all 4 if the front bleeder valves weren't new. Then re-bleed the system. Also inspect the caliper pistons for leaks or sticking pistons.

 

i would have to agree with Pa,,,,, it acts like air in system, or a leak or a bad master cylinder ,, have you checked all of the system?? lines? hoses ? caliper sliding free? pistons moving free? push rod length ok ??

I am not a fan of auto zone master cylinders they are for the birds but you replaced it twice and still same issue it is highly unlikely but not impossible that both masters would be bad ..

 

Everything all right at the wheels?

I'm not sure if any Hondas are like this, but some cars you can position the anti-rattle spring incorrectly, and it pulls the pads away from the rotors. That would act just like you describe.

 

Thanks for the advice! I replaced the ABS bleeder which I noticed was leaking a few bubbles during bleeding. The 4 at the wheels seem ok but on your advice I ordered a set. Should be in later tomorrow.

The right rear brake was stuck. Pads, guides and shims rusted together and the caliper didn't want to move. Looks like the previous owner didn't have rear brakes for a long time, or it just sat somewhere. Will need to replace the pads & stuff, but I cleaned them all up and greased the sliding surfaces, then dismantled the caliper. No rust inside, just sticky. Cleaned, flushed, lubed seal with new brake fluid, filled and operated the caliper back and forth off the car. Reassembled, bled and did the same to the other side, which wasn't as bad. Both rear brakes seem to work now.

If the rear calipers are worn, i have no problem replacing them. What confuses me is this... if I can pump the pedal once or twice and get plenty of brake as long as I hold it in, wouldn't that mean the calipers and push rod are ok? And if I let go and the system goes slack, but there are no leaks, puddles or sign of fluid draining anywhere, where does all that hydraulic pressure go?

Guess I'm frustrated because the seller said it only needed a front caliper, and with all I've done I still can't use the car or get it registered. This system doesn't act like other cars I've worked on so I'm trying to understand it better rather than just throw parts and money at it hoping it'll get fixed.

I do appreciate all the advice so far! Thanks.

 

The brake system really isn't that different from any other make of car. It's not SUPPOSED to act different from the other cars you've worked on.

When you installed the brake master cylinder, did you measure the length of the push-rod to see if it's exactly the same?

There's a gasket between the MC and the vacuum booster. Did the old one stick to the booster leaving you with 2 gaskets?

When you did the rear caliipers, did you twist the pistons to retract them? You know not to push them straight in with a C-clamp like the fronts?

I agree about figuring this out rather than throwing part$$ at it.

 

On the front calipers are the bleeders at the top or bottom you may have the sides reversed. If the bleeder screws are at the bottom you will never get the air out and the calipers on are the wrong sides.