Hi I have an 86 Honda Accord. This morning, the brake pedal started going all the way to the floor. It will pump up a bit firmer after a few pumps, which is not really acceptable. I had a similar issue about 4 years ago, replaced the master cylinder and the cylinders for the rear drum brakes. bled it many many times, and eventually it started working again.
Been fine for years until this morning. I tried bleeding them, went til I saw no air bubbles then went a bit more. Noticed the rear right drum was stuck in, so i adjusted the star nut.
Not sure what else might be going on!
Any help welcome!
Bear in mind, the MC is relatively new.
Have the car towed to a mechanic.
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Look for leaks. If no hoses, calipers, or rear cylinders are leaking, the master cylinder has probably failed again.
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Agree with @Scrapyard-John , master has gone out again.
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It’s very hard for me to believe the master went out after just 4 years. I am coming to this forum looking for perhaps another suggestion. In my experience the master rarely goes out. In fact, I replaced it because of getting similar advice and it didn’t fix the problem last time. just plenty of bleeding eventually did it. Curious how it happened overnight? It has been quite hot. Also, the front left wheel was hotter than the rest. I suspect it was doing more work due to the rear being seized up and boiled some fluid.
It would be hard for me to believe that the MC could be bad also, but: if there are no leaks anywhere, and there’s no air in the system and you have completely looked at each corner for something wrong, then the MC is the next and most probable cause.
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Ok NEW information not shared. Anything else?
If you boiled the fluid the fluid it needs to be replaced and bled.
If you boiled the fluid… Why?? Stuck caliper or… bad brake hose? Have the hoses ever been replaced?
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What is your brake fluid level? If not low, master cylinder is probably the problem but when corrected would also advise a flush and serious look at all the wheel cylinders.
It’s a a 30+ year old car so it’s safe to assume that all your seals are bad and maybe your rubber brake lines too.
I’d suspect the front left caliper is sticking, or the hose is collapsed internally if it’s getting hotter than the rest.
Replaced several on my old Jeep’s and replaced one on my former Dodge Ram. I wouldn’t say it’s rare for one to fail (in my experience). If the 4 year old one is a parts house brand, I wouldn’t be too surprised if it’s out again. If the brakes (rear) are adjusted correctly, all the pads and shoes are in good shape, the fluid level is good, and there are no leaks, I can’t see much else other than the master that would be the cause of the mushy pedal (other than air in the system - but if you haven’t opened it up and there are no leaks…shouldn’t be any air in there).
I’ve never had a problem with the brake booster failing, so I don’t know what symptoms that would cause. You might could plug the vacuum hose to the booster to take it out of the equation somewhat and see if you’ve got a firmer pedal, but I don’t see it affecting the system that way unless the master cylinder is leaking into it…but that’s a master cylinder problem again.
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Yeah agree with the others. Those were always the symptoms of a master but check the other issues. In the past I have rebuilt one or two and they just have rubber plungers that can wear or deteriorate. But so can the other brake parts.
If I had this problem on my early 90’s Corolla I’d take a look-see at the front calipers and rear wheel cylinders. If no signs of brake fluid leaking (including from he brake hoses & fittings) I’d replace the MC. If the brake fluid got really low for some reason prior there’s a chance you just need to bleed the system again. The problem is that it is very easy to damage a 4 year old MC with diy’er bleeding unless you have access to the equipment needed to do a pressure bleed procedure.
thank you. isn’t it the case with an MC leak that the pedal slowly sinks to the floor tho? in this case it goes straight down the first time and firms up with successive pumps. replacing the shoes now bc i noticed one was quite thin. Don’t think that’s the problem, but just an update.
going to bleed again soon. For reference, honda manual says FL, RR, FR, RL
I did not do that. will do it this time!
I also saw a vague reference to drums and shoes leading to issues like this. Can’t find it now.
It’s hard to say what the symptoms will be when a seal in a hydraulic system leaks b/c it is possible pumping the pressure up will swell the seal & close the leak (temporarily). It’s also hard to tell which seal is leaking. The clues are that if there’s no obvious external leak it will usually be the MC, b/c it is the only one that can leak internally. If you have ABS, that unit can develop internal leaks too I think.
I’ve always done farthest from MC to closest. RR, LR, RF, LF. But, if the manual says otherwise, I’d go with that.
If they’re bad out of adjustment, you’ll have a low pedal, I guess. But I don’t think you’d really be able to “pump up” the brakes in that case because the shoes will still have the same distance to travel on the second pump as they did the first.
Good luck with it. Let us know how it goes.
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That says that corner was dragging creating heat which could boil the fluid. Pumping the pedal can bring it back but… you need to fix the drag… caliper piston or slides sticking or a failing brake hose which makes it act like a check valve holding pressure to the caliper or wheel cylinder.
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The master cylinder creates the hydraulic pressure for the brakes to function.
If you step on the brake pedal and it goes to the floor, there’s no hydraulic pressure.
Tester
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A loose wheel bearing can cause this. The brake rotor tilts causing the caliper piston to retract. Do you get the same rection while on jack stands?
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ok just finished replacing the shoes and giving another bleed. I’m not sure why people hate on drum brakes I only had 3-4 rage blackouts that I can recall…
The good news is, the pedal has firmed up quite a bit.
The bad news is I did something kind of stupid while seeing red. I used the drum as a bit of an improvised hammer to get the horseshoe clip off one of the e-brake cables. 
Now that wheel (RR, not the one with the worn heel) sounds CRaZy like grating metal. I obsessively check for wheel bearing sounds by rocking at 3&9 and 6&12 and don’t hear a click or anything (tho the suggestion that a worn bearing could cause uneven wear fits right in with my fears), but turning that wheel sounds terrible. I took the drum off and rotated it 180 degrees, the sound is consistent with a certain side of the drum (I imagine the business end of the hammer)
I am already ashamed so please go easy on me, we all make mistakes right? Now I’m wondering if this will round itself out or if something will catch on fire?
Thank you all for your help!
What!
No rocks around?
Tester
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This has nothing to do with solving your problem, but I have had no difficulty bleeding the brakes since I went to a one man bleeder.
It is basically just some clear plastic tubing that fits snug over the bleeder and a jar elevated over the bleeder with enough fluid to cover the end of the tubing. have the master cylinder full and the bleeder cracked open and slowly put the brake pedal to the floor and back up On my car I could do it 3 times without emptying the M/C. Close the bleeder and you aere done with that wheel.