Hi. I have a 1999 accord. It has a sunroof and a 2.3 L 4-cyl V-tec engine. I assume this makes it an EX. JHMCG5550X are the first 10 Vin digits.

My brake pedal goes to the floor. .way way down. Then it hits a hard spot and the rear brakes apply.

After viewing http://www.tegger.com/hondafaq/mastercylinderreplace/index.html
I decided I had a bad master cylinder for several reasons. I had No external leaks at the wheels, at the flexible rubber hoses, or the hard metal lines going to the ABS unit and the master cylinder, The fluid level has not dropped in the reservoir, and I've taken the cap off and looked inside to make sure it didn't. There is a rushing fluid noise when I press the pedal down.. Like the noise Hydraulic lifts make when they open a glass hatch or a hood.

I followed the easy to follow instructions at Tegger.com for replacing it and still have no pedal. My New master cylinder came with a bleed kit and I used it on the front and rear circuits to remove the air while set in a table-top vise. I pushed the plunger fully down and released it to make sure no air was left. This took about 15 plunges to remove all the fine bubbles.
Thinking I had let air get into the lines during the swap even though I saw no fluid leaking out of the lines when I removed them. I bleed the brakes . Started with the Left Rear then the Right Rear then the Right front then the left front. This info came from one of those Haynes manuals I looked through at AutoZone and have seen it also on-line. I used a one-man pressurized bleeder and let the fluid run out at full stream till it was the same color as the new fluid for all the wheels.. I didn't see much if any air and I was expecting a lot considering how the pedal is acting. I tightened all the bleed screws and even after doing all this
,the pedal goes to the floor when I press it, then hits a hard spot and the rear brakes apply, Same as before. So now I have a fully bleed brake system with a new master cylinder and Just rear brakes.

I'm highly mechanically inclined, I can read diagrams, troubleshoot electrical, etc. I need some help on this. A car that applies only the rear brakes is going to get me killed in a 45 minute commute.

The car has ABS. The ABS light bulb functions when you start the car.. then goes out. The same for the BRAKE light.


HELP!!

 

Just wondering,do you have 4 wheel disc or drums in the rear?

Did you pump the pedal until it got stiff before starting the car?

If so,did the pedal fall to the floor when the car was started?

Did you pull the MC off with the lines connected to see if theres any fluid leaking out the rear seal?Even with the new unit?Reman and new ones are sometimes bad outta the box.

I did not see you said ya checked that.

Since you seem very inclined,you know the basics of a hydraulic system,if it has any air or leaks,will continue to do what youre experiencing.So we have to go from there.

Theres also a chance you have a bad proportioning valve..its very rare,but can happen.The valve is supposed to apply more fluid pressure to the front,then the rears.I have also seen rear wheel drum cylinders go bad,but not show any leaks right away.

There is one homemade test you can try...it may not always work,but has on some cars I did it on.

At the master cylinder,I took off the lines to the rear and put a nail that had a head that fit perfect inside the line and closed it back up.

That stopped any fluid from going to the rear.Only the front brakes would get fluid and was able to track down any problems going on in the front.

 

Vehicle has 4 Wheel Disc brakes.

The pedal is hard once the vacuum stored in the brake booster is depleted. but will travel to the floor if you hold the pedal down.

The pedal will not fall to the floor under its own weight. Applying light foot pressure similar to waiting at a traffic light on a level road in neutral is enough to make the pedal bleed to the floor with or without vacuum boost.

The first thing I did when I suspected the old master cylinder and verified there were no external leaks was to remove the booster line from the manifold and check for fluid inside the line.. there was none.. Next I unbolted the master cylinder from the booster and checked the rear seal of the master cylinder. No fluid at all. I have not Checked the new unit for a leaking rear seal, and honestly I see no reason too, But I can humor you by checking tomorrow. I sincerely doubt the old part was broken at this point since it exhibits the exact same noises and pedal feel as the new unit, even after my best efforts to ensure I installed it correctly.

I don't know what the symptoms of a bad proportioning valve would be. Doing a quick check it doesn't seem to be a popular part, I don't see it on Auto zones site under the vehicle parts list at-least.

Seems I can order one from Honda for 50-65dollars depending on where from and shipping etc. I'm not real big on throwing parts at a car. I learned alot watching my dad do that. If I can understand how this proportioning valve works I may be able to understand how it can fail.

 

From working as a mechanic if you have no leaks and the pedal goes to the floor you replace the master and every so often it turns out to be the proportioning valve. I have seen some other strange things but not on a Honda. With drums you also need to make sure the shoes are adjusted correctly but not a worry with Honda rear disc.

 

Can any of you explain what is happening in the proportioning valve when it goes bad?
If I've got all the air out and I'm left with just fluid in the lines, and the master cylinder is pushing the fluid through the lines without leaks, but the fluid doesn't make its way to the calipers to apply the front brakes, where is the fluid going? You can't compress the fluid so it has to be going somewhere.

I'm liking this proportioning valve idea I just really want to understand what's happening in the thing to cause these symptoms.

 

The proportioning valve decides what percent the front and rear brake system receive to stop the car. The front if the valve is working correctly receives the most. I think it is something like 70%. How it does this I don’t know. Over a decade I can only remember one vehicle where it went bad but has the same symptoms of the master.

 

I read this again tonight,and Im starting to wonder if you have a bad brake booster...that can make the pedal feel low and very hard to stop,and makes a noise if it is leaking.

The fact that you hear something is what gets my thinking going.A leaking booster will not hold vacuum and make a noise.Brake boosters when they go bad,give you a low,very stiff pedal,and make a noise from the vacuum leak.

I am NOT saying throw parts at the car,just something to think about or check in the meantime.

With the car OFF,pump the brake pedal until its firm.Then,hold the pedal down and start the car.What does the pedal do?It should go down a little bit,but not go to the floor.

Does it still sink down?How much? If so,if you pump the pedal does the pressure come back?

Im very curious about this.

 

Hey 96fivespeed, the car has sat for a few hours (about 5).. Without turning it on I pumped the pedal to check the vacuum stored in the booster. I got a little over 3 assisted pumps then the pedal became more difficult to move. I held the pedal down without starting it, and it sank to the floor. A little different from your suggestion but I wanted to see what it did after sitting and not starting it. The sound I described persisted with and without vacuum, and only happened when the pedal was traveling. This seems to be reason enough to believe the booster is holding vacuum. 5 hours not running, it's holding it well.
I did start the car to build the vacuum up again and repeated using your instructions, but the pedal slowly traveled to the floor, till the rear pads locked against the rotors, ( took about 3 seconds) there seems to be no "pumping the brakes up" on this car.. the pedal just leaks down.

I have other theories. I want to eliminate the rear circuit entirely. I plan to plug off the ports from the ABS unit to the proportioning valve and See how the pedal acts.. if I suddenly have front brakes again I'll replace the valve.. if not I'll continue diagnosing. I doubt the lack of front brakes has anything to do with the rear circuit and this will help me decide.

From what I've been reading.. ABS uses an accumulator to store pressure for the unit to work with then it is functioning. There are two types. A nitrogen filled gas bulb with a rubber membrane separating the brake fluid from the nitrogen gas.. and a spring loaded piston that applies constant pressure against a volume of brake fluid. I've been looking at the ABS unit and I see no screw on gas accumulator. I could have the spring loaded type.
If for what ever reason... My spring has broken, then my piston in the ABS unit will be free to move. This could explain where my fluid goes if it doesn't reach the front brakes but doesn't leak out of the vehicle. The noise I hear could be fluid moving quickly through the lines as it fills the piston bore in the ABS unit.. then I release the pedal and the fluid travels back where it came from.. the master cylinder. Since the port for the master cylinder only opens when the pedal is resting fully open it will suck the fluid out of the piston bore and the fluid level in the reservoir will not change.

I asked myself if this is the situation, Why aren't all the wheels affected.. I've decided that two spring loaded accumulators one for the front wheels and one for the rear, would provide a possible answer.
I'm looking around to see if I can find any diagrams for the inside of the ABS unit on my car to help prove my hypothesis.

This may be a wild and crazy explanation, but I'm believing this isn't a typical problem I'm dealing with. I hope to have the time to carry out all my tests and report back with my findings.

 

Good Luck and do keep us posted.Im very curious myself.Im wondering if the abs unit or p valve or something somewhere,theres a pressure loss or internal leak that just hasnt showed its ugly rear yet.

Hope ya find it soon.

 

Any progress?

I wanted to share this with you...I dont think it is whats wrong,but hey,one never knows.Im a member of a corvette forum and someone posted this...might be something to check.



I know I am not the only guy that has complained of a hard brake pedal on a late model C4. My 94 brakes have always been terrible, In spite of upgrades over time of new rotors, quality pads, stainless lines, J55 upgrade, and a new M cylinder. The brakes still sucked. They always felt like they had no boost even though the unit checked out and worked normally. I finally broke down and decided to let someone else work on my car (I hate doing that you know) by taking it to Corvette Masters in Orlando.

With the ability to read the ABS unit it turned out that there were 3 codes stored in my computer. Even though the light came on when you started the car, the ABS went through the self check and then the light went off, ( in other words it acted as it should) the 3 codes that were in it were somehow preventing my brakes from working normally. They cleared the codes, went through the diagnostics on the unit to insure it was OK, and voila! I have brakes now.

I know I have seen lots of guys complain about this, and I would have never suspected the solution could have been so simple. So if your brake pedal requires way too much effort to stop the car and there seems to be no reasonable solution to it, I would strongly reccomend you have someone look into the ABS units subconscious mind and perform the necessary brain surgery.
Thank you Corvette Masters!