I have a 1992 Honda Accord with about 220,000 miles on it. The car was parked about two years ago mostly because my wife wanted something four wheel drive. I decided to save the car for my boy that has turned 16 and now has his license. I've done quite a few maintenance items on it and now I am working on the brake system. Before we parked it it had a sinking brake pedal and I assumed it was the master cylinder. I put a new one on 2 years ago, bench bleed it and all that, and still had the sinking brake pedal issue. That's about when we parked the car. Fast forward to now, I did a test for a bad brake booster and that seemed to be the issue so I put a new brake booster in it. I also refurbished all of the calipers and it has new pads and the entire system has been bled multiple times. With the car not running I have a pretty solid pedal and it does not sink. If I pump the pedal and hold firmly and then start the car the pedal will pretty much sink to the floor. At this point I'm scratching my head wondering if there is an issue with the ABS. I've done a fair amount of research and talk to other people and several said it's the ABS pump. Obviously I don't want to start throwing more parts at it unless I know for sure. I took it for a test drive a few days ago and, I can romp on the brakes and it will definitely stop the car but, the pedal does not feel firm and will sink. Is it the pump? The modulator? Air in the ABS system? I would really really appreciate some input here. Thank you....

 

The ABS system will not cause this issue. Are the air bleeders on the calipers pointing up towards the sky? It is possible to switch the right and left, where the bleeder points down.

Look at each rubber portion of the brake hose going to the caliper. Have an assistant push on the brakes. See if the rubber hose bulges in any section.

 

Another thing that I've seen occasionally is one last stupid air bubble hanging out in the system. I bleed & bleed until I'm sick of doing it, with no bubbles coming out at the calipers. Still soft. Bleed some more and after getting a bunch of nice fluid, I eventually get the last couple bubbles.

Never figured out where those bubbles were hanging out, but they came out the rear calipers. Maybe the proportioning valve? Anyway it was frustrating thinking I was just wasting fluid - until the last bubbles came out & it was good then.

 

Well, it's always been my understanding more or less that, the General braking system works separately but yet in conjunction with the ABS. Am I correct here? So, if the ABS is not working correctly I still have normal braking function just not abs. I suppose that's part of my confusion under normal braking I get the sinking pedal. Yes the air bleeders are pointing upwards. Why do you feel as though I should swap them left to right so that they are pointing down? And, if I do swap them will I actually have enough brake hose to get to the swapped calipers and will the emergency brake cable still work as far as the length goes ? And, if I have a solid pedal when the car is off why do I get the sinking pedal when the car is running? Is it because of the exponential pressure being put on the system because of the power booster? And, as far as having an assistant push on the pedal and look for bulging and any of the soft hoses, would I be able to see any bulging when the car is not running? Or should this be tested when the car is running?
The other gentleman that responded said it could also be the break proportioning valve. Is this also a possibility? Is there any way to test it? Thank you very much for your input this is starting to shed a lot of light on things.

 

Yeah, I know what you mean about one last little tiny air bubble still coming out. And I definitely know what you mean about wasting brake fluid. After all of this I know I've gone through a quart and a half. After I replaced the power booster and bench bleed the master cylinder I went around and bleed each caliper three to four times individually, and then went around and did all of them all over again and yes, I still got just a couple of little air bubbles out of the rear calipers. After doing all of this I have a fairly solid pedal when the car is off. It's when the car is turned on and I put my foot on the break is when I get the sinking pedal. Why do you think that it might be the proportioning valve and, is there a way to test it? When I was bleeding the brakes I have the car up on jack stands with the wheels off. I had My assistant very slowly push down on the brake pedal until the pads were just barely grabbing. I had him hold that position and all four calipers were grabbing fairly equally as far as I can tell. I had him pushed just a tiny bit more and they were all grabbing very equally. So this kind of pushes me in the direction that it is not the proportioning valve. Any further thoughts I am absolutely all ears. Thanks a lot for your input.

 

PA isn't suggesting you swap the calipers to make the bleeders point down. He wants you to confirm that they ARE pointing upwards like they should. I've seen a thread where someone put their calipers on the wrong corners and had the bleeders pointing down, so it was not possible for him to remove the air from the caliper. Probably was on the front because like you say the handbrake cable would be all wrong.

If someone watches the rubber hoses, you'll want to press the pedal hard-enough to make it sink and duplicate the problem. If that's the problem I think the dilating hose will be visible.

I only thought of the proportioning valve because it's really the only component in the rear system, other than steel tubing. It's job is to lower the pressure to the rear, after you are pressing down pretty hard on the pedal. If you're braking hard, this prevents the rear wheels from locking up too easily. The proportioning valve should do nothing until you're pressing pretty hard on the pedal.

PS:
I just looked and it seems like only the LX & DX (rear drums) have the proportioning valve. The EX (rear disks) doesn't have a proportioning valve but it has some kind of 4-way connection block instead.

 

Okay. Thanks for clarifying the swapping of calipers. That totally didn't make sense to me. I'm glad you cleared it up. And yes, as far as what the other gentleman said duplicating the problem, it seems to me as though I will have to have the car running in order to duplicate it. That is when I am having the sinking pedal.

 

And yes, you are correct about the proportioning valve. It looks as though there is just a splitter block like you said that is down underneath of the power booster. It doesn't necessarily really look like a proportioning valve of any type just a splitter. Thanks for the further information

 

There's several places where the brake lines go "downhill". Do you think you are bleeding the brakes too slowly and allowing air bubbles to move back uphill in between bleeding strokes?

 

It's possible that I have allowed air bubbles to move back in but, that still doesn't explain the solid pedal when the car isn't running and then totally sinks when I turn the car On. I'm still thinking about taking the master cylinder back out and rebench bleeding it. and then bleeding the entire system again. Overall I don't think I'm going to get any drastic difference but, it will give me a piece of mind that I've gotten all of the air bubbles out. Then I will go from there and try to recreate the problem and look for bulging soft lines or mysterious leaks that I haven't seen.