Mechanics

BRAKE PRESSURE

1994 Honda Civic • 4 cylinder 2WD Automatic • 227,000 miles

1994 Honda Civic ABS, Lx. I have all disc brakes. I just installed new brake pads on all four. I bled all four brake systems the proper way, starting from rear right, front left, rear left, then front right. The brake pedal still has little to no pressure. When I apply pressure on the pedal when the engine is off, it starts with no pressure (goes all the way to the floor) then after a pump or two it has some pressure but never maintains the pressure, pedal goes to the ground slowly. I turn the car on and there is never pressure, it goes to the floor all the time basically. What suggestions do you have to solving this pressure problem? Would flushing the brake system help at all?
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Sum2
April 11, 2011.




Sounds like internal leakage inside the master cylinder. That is commonly caused by running the pedal all the way to the floor during bleeding. Crud and corrosion build up in the bottom halves of the bores where the pistons don't normally travel. When the pedal goes all the way down, the lip seals get ripped on the corrosion. It's okay to go all the way down with a new or rebuilt master cylinder, but with an old one, pretend there is a block of wood under it and never go more than half way to the floor.

The clue to determining if this is what happened is to pump the pedal rapidly to see if it will build pressure, then hold it but if necessary, ease up on the pressure a little then push harder again. If the pedal suddenly falls away and there's no external leaks or loss of fluid in the reservoir, suspect the master cylinder needs to be replaced.

Caradiodoc
Apr 11, 2011.
I suspect it is the master cylinder also. I'll look into getting it replaced and update afterward. Thank you so much for the quick and thorough answer!

Tiny
Sum2
Apr 11, 2011.
I forgot to mention the motor revs up slightly when I apply the brakes right now. Any clue what is going on?

Tiny
Sum2
Apr 11, 2011.
I wouldn't worry about that just yet. If the brake pedal is moving with little pressure, there might be a lot of vacuum being lost in the power booster with each stroke. The engine will respond just like if it had a vacuum leak but the engine speed should come back down in a few seconds if you hold the pedal down.

Caradiodoc
Apr 11, 2011.
Do you think I would need a new brake booster also? Or only the master cylinder?

Tiny
Sum2
Apr 11, 2011.
Just the master cylinder. I never heard of a bad booster in all my years of mechanicing and teaching, ... Until a few years ago. GM owners have their own set of problems, but for the rest of us, about the only thing that can happen is the diaphragm develops a leak. You will hear the hiss when you press the brake pedal. That opens a valve to let atmospheric pressure in so the engine vacuum can pull on it.

Caradiodoc
Apr 11, 2011.
When replacing/repairing the master cylinder, before reinstallation, ensure the seal between the master cylinder and booster is in good condition. The seal tends to fail resulting in vacuum leakages.

KHLow2008
Apr 11, 2011.
Thank you cardadiodoc and KHlow2008 for the helpful advice. I'm now going to work on the car. I'll update when I can. Thanks again. This forum has been very helpful in troubleshooting this frustrating problem!

Tiny
Sum2
Apr 11, 2011.
So I changed the master cylinder today and the problem is still the same. I bled all four brakes and the brake pedal still goes to the floor when the car is turned on. Any ideas?
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Tiny
Sum2
Apr 12, 2011.
If you have the parking brake built into the rear calipers, it's possible they aren't adjusted up yet. I'm not real familiar with Honda's rear disc design, but for some other brands, the rear pistons will not self-adjust out from just pumping the brake pedal like in front calipers. The rear pistons will move out like normal when you press the pedal, but they will go back in when you release the pedal. What you may have to do is work the parking brake multiple times to walk the rear pistons out until the pads contact the rotors. If the cables are rusted tight or you don't trust them, you can use a pliers to work the levers on the calipers back and forth until the pistons come out.

If you have this design, you wouldn't have been able to just push the pistons back into the calipers to fit the new thicker pads in. You would have had to use a special tool to screw the pistons in.

Caradiodoc
Apr 12, 2011.

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