I have a 1990 Honda Accord, and I am an aspiring mechanic in school for automotive repair. I had an issue with brake fade (at odd intervals, sometimes the brakes were perfect, sometimes the pedal would sink alarmingly quickly to the floor, and everything in between). After a time, and it gradually getting worse, I decided it was time to replace the brake master cylinder!
I slapped in a remanufactured master cylinder identical in appearance to the one in my car. I bench bled it, installed it, and bled the brakes in every manner possible (Starting from farthest from master cylinder, to closest, then by the book, as the brakes are linked on opposite corners) and had little to no brakes. Fluid drained freely from the bleeders, and I’m 99% sure there was no more air in the lines. I decided I got a bad reman’d part, took it back, and bought a new one instead. I went through the same procedure, and had no luck. I am now on the third master cylinder, and I am having no luck.
The pedal will travel straight to the floor. I did try running the car (booster is fine) and applying the brakes, and when I drop the pedal to the floor, I get VERY MINOR braking. Enough to stop the car on a 10 degree decline (my driveway), but not enough to stop the car when it is in gear (automatic). As a sidenote, my e-brake now requires more travel to engage fully.
It is disc front, drum rear, and I thought to adjust the rear pads. They now just barely rub the drums. I can see the pistons on the rear wheel cylinders move out a good amount, but the pressure is still apparently too little to matter.
I bought a hand-pump-operated vacuum system to aid in brake bleeding, and teflon taped the bleeders to avoid false-air bubbles, making sure to keep the bleed holes clear. It worked a treat, and I’m certain there is no air in the lines. I’ve used approximately 8 liters of brake fluid during the 2 weeks I’ve spent trying to get my brakes right, and my driveway is NOT happy about that.
I AM LOST! Car Talk, I need your help!
You seem pretty certain there is no more air in the lines. And you’ve done enough bleeding to prove it, including bleeding the master. I’m assuming the brake fluid isn’t leaking out at all. One thing you might check are the rubber brake hoses. There may be a tear in the interior of the rubber lines and the line is just expanding when you apply the brake. You may be able to observe the expansion by looking at the lines individually while someone repeatedly presses the brake pedal to the floor. That would be my next thought anyway.
I forgot to mention that I did just that - There isn’t very much rubber on this vehicle - only where flex is necessary (near suspension and brakes actual) I would estimate that there is only a half-foot of rubber line per wheel, and I noticed NO visual change as far as expansion is concerned. I’ve spent nearly 40 hours trying to figure it out, and I gotta say, I’m stumped! There is no visible trace of fluid leaking. I’ve run enough fluid through the entire system that, even if the leak was hidden behind something, I should have eventually leaked enough to make a huge puddle. I also rebuilt the rear wheel cylinders - no leak there.
On the bright side, I also have a 1993 Honda Accord project (read - ‘spare parts’) car. It is the same body style, and is practically identical on all practical levels. The brake master cylinder has two lines that come out. I am certain one operates front left - rear right, and the other operates front right - rear left. Both lines go to a contraption that basically resembles two Y’s stacked on top of each other. Both the lines from the master cylinder go to one branch of each Y, and the other branch goes to a front brake, while the bottom part of the Y goes to a rear brake.
Here is a picture I found on the internet -
http://www.jdmjunkyard.com/auctions/030607/prop4.jpg
Is this the Proportioning Valve? This is the only thing I can think of that might be the problem, if the failure is mechanical.
As a sidenote, the car is NOT level to the ground. I didn’t think this would matter, but my driveway is inclined, and in order to access the rear bleeders, I had to lift and jack-stand the rear wheels - so the angle is even STEEPER (the car is backed into my driveway, nose pointing down). I know that there is some sort of system in place that is supposed to lower brake pressure to the rear brakes (and perhaps redirect to the front) if the car is pitching forward, but I do not know if my car is equipped with it, or if it is even an issue. Could this be where I am going wrong?
There is no Brake warning light, but then again, the car is OBD1, and I don’t remember there even being a light of this description.
I’m still stumped!
“I know that there is some sort of system in place that is supposed to lower brake pressure to the rear brakes (and perhaps redirect to the front) if the car is pitching forward”
I’ve never heard of such a thing. The proportioning valve limits the pressure to the rear brakes. I’ve never seen or heard of one failing.
" I’ve used approximately 8 liters of brake fluid during the 2 weeks I’ve spent trying to get my brakes right, and my driveway is NOT happy about that."
Sounds like you’re letting the fluid run out on the ground? I use a clear plastic hose on the bleeder that drains into a jar. I get a helper (wife) to pump the brakes.
Try pinching off each rubber brake hose one at a time to see if the pedal improves.
Problem Solved. SOLD THE CAR!
Just kidding. As it turns out, the front brake calipers can be mounted upside down. Therefore, the brake bleeders were down instead of up. A good bleed of the brakes would result in the fluid running out and air creeping back up into the bleeder valves. But only just a small amount of air, so as this is --A-- problem, it was not --THE-- problem.
The problem stemmed from the metal lines going to the master cylinder itself. It is a metal-to-metal crush fit, and as such, basically is only ever ‘perfect’ only once. There is a process called ‘flaring’ that had to be done to the metal lines as they meet the master cylinder, if you didn’t end up one of the lucky ones who could just plug em back in when you changed out your master cyl. Because pictures are worth a thousand words, here’s a website that details the proper “re-flarification” of brake line:
http://www.fordification.com/tech/doubleflare.htm
Basically, brake line is like a straight tube-y pipe. It must be warped and crushed into a more or less cone shape, which I assume makes it easier to crush-fit and seal onto the master cylinder. It was because these lines were not sealing properly that I could never good brakes, as the fluid simply seeped out and air crept in every time I pumped and let out the pedal.
To solve the brake caliper air problem, I removed the calipers from their mountings, stuck blocks of wood between the pistons, flipped them upside down, and hung them from the suspension from hangers so they would bleed properly. Then I bled em, and stuck em back on. A lazy fix, but a fix nonetheless.
Voila! Perfect braking was achieved.
Sincere congratulations on figuring this one out and fixing it. Stick around. We can use the help.
The single most valuable tool we have isn’t in out tool chest; it’s in our heads. Yours is top grade.