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Brake pedal goes to the floor?

Tiny
JEFF HERMAN
  • MEMBER
  • 1995 HONDA CIVIC
  • 1.5L
  • 4 CYL
  • 2WD
  • MANUAL
  • 120,000 MILES
This vehicle has rear drum and front disc brakes. Shoes and pads are good. No ABS, so it's a pretty basic system. With all that said, the pedal goes to the floor when braking. All four corners have been bled and basically all the old fluid has been flushed out. When you pump the pedal, it firms up and holds but if you let off and depress it then it goes to the floor. No visible leaking out the back of the master and no cracked vacuum lines on the booster. It does appear to mainly only have front brakes. Is this a proportioning valve issue or a bad master cylinder?
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Thursday, August 10th, 2023 AT 5:02 PM

20 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

If there are no leaks, the brake master cylinder is the most likely cause. Do me a favor. With the engine off, pump the brakes to get a solid pedal. Then, hold pressure on the pedal for a bit to see if it starts slowly going down. If it does, then we know for sure it is the MC.

Take a look at this link:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

If you decide to replace the master cylinder, make sure to bench-bleed the new one before installing it.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

The pic below are the very basic directions from the manual.

Let me know if this helps or if you have questions.

Take care,

joe

See pic below.
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Thursday, August 10th, 2023 AT 10:01 PM
Tiny
JEFF HERMAN
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  • 449 POSTS
When I pump the system up to get firm pedal it seems to hold most of the time but if I just let off slightly it goes straight to the floor.
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Thursday, August 10th, 2023 AT 10:44 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Jeff,

I suspect it is the master cylinder that has failed. There are plungers in the MC that can fail and allow fluid to bypass them. I believe there is an adjustment on the push rod, but you didn't remove the MC, so that shouldn't be an issue.

That leaves the master cylinder. If there are no leaks, the rubber brake hoses at the front calipers aren't expanding, and the fluid level in the MC doesn't go down, the master cylinder is my first suspect.

I attached information related to the push-rod adjustment and clearance. Take a look below. However, unless you had things apart, I don't feel this is the issue.

Let me know.

Joe

See pics below.
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Friday, August 11th, 2023 AT 9:29 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 449 POSTS
I did find a leaking hard line up front but same results after re-bleeding. I removed the master and took it apart to find the front seal halfway chewed up. Ordered a remanufactured master and when I went to pick it up somebody's core was in the box. We'll see what happens tomorrow when I get the master. When did bench bleeding the old way change to cycling fluid from the ports back into the reservoir? Doesn't the old way work and is it necessary to bleed again once it's installed?
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Friday, August 11th, 2023 AT 9:46 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Thanks for the update. I had a feeling that was the problem. Interestingly, if you had a hard line go out causing the brake pedal to go to the floor, that is likely when it happened.

Over time, corrosion builds up in the areas where the plungers don't travel. When the pedal suddenly goes to the floor, the plungers are forced through that area causing damage to the plunger.

Let me know if this resolves the issue. Also, I'm not sure what you mean by the old way of bench bleeding the master cylinder. Could you explain how it was done? I'm interested in knowing especially if it saves time. LOL

Take care,

joe
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Friday, August 11th, 2023 AT 10:48 PM
Tiny
JEFF HERMAN
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We just let fluid start to run out the ports and then put plastic plugs, which used to be included when you bought a master cylinder, in the outlet ports and compressed the piston several times until it was firm. Then I installed it.
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Friday, August 11th, 2023 AT 10:56 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

No, that won't get all the air out. Basically, you are gravity-bleeding it. Can it work, yes, but you should bleed it using the plastic tubes. I gravity bleed new calipers or new brake lines, but I also pressure bleed them once I get a stream via gravity.

If you need help or have questions, let me know.

Take care and let me know how things turn out for you.

Joe
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Saturday, August 12th, 2023 AT 8:12 PM
Tiny
JEFF HERMAN
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  • 449 POSTS
I put the new master in and it came with the plugs and tubes. The brakes work good and go nowhere near the floor. I think the rears could be adjusted out farther. I tried holding the brake pedal down and pulling up on the parking brake and I tried going in reverse and braking hard. The star adjuster can't be reached from behind with the drum on. Also there didn't seem to be any way to adjust the pushrod. The pedal barely moves before I hear the rod hit the piston. PS we bled master cylinders that way before the recycle method or vacuum bleeding and it worked fine. Before ABS and electric assist and vehicle stability.
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Saturday, August 12th, 2023 AT 8:26 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Thanks for the update. It sounds like you got things working properly again. If the push-rod isn't adjustable, maybe it is a different model or something.

About the ABS bleeds, all I can say is UGH! They can be so frustrating. Things haven't gotten easier, and I question if they have gotten better.

Take good care of yourself and feel free to come back anytime in the future.

Joe
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Saturday, August 12th, 2023 AT 8:34 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 449 POSTS
Thanks for your assistance, I don't really think they've gotten better but they've certainly gotten more complicated and difficult.
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Saturday, August 12th, 2023 AT 8:54 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 449 POSTS
How are you supposed to use the auto adjust or is it easier to do it manually?
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Sunday, August 13th, 2023 AT 6:34 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I attached a pic below showing what I believe you are dealing with. As far as the self-adjuster, it is supposed to adjust when you back up and hit the brakes. I've never seen them work correctly.

Do it manually. Remove the drum and measure the inside of the drum and the outside of the shoes. Install the drum and before putting the wheel on, get in and pump the brakes a few times to seat the shoes and then recheck them.

Let me know if this helps.

Take care,

Joe
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Sunday, August 13th, 2023 AT 9:26 PM
Tiny
JEFF HERMAN
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They can't be far off because the hand brake locks up in 4-6 clicks. I read it should be 6-10 clicks. Is there a way to get to the star wheel from the hole the rubber plug is in?
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Sunday, August 13th, 2023 AT 9:47 PM
Tiny
JACOBANDNICKOLAS
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Hi,

Is the rubber plug on the rear of the backing plate or the drum?

Joe
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Monday, August 14th, 2023 AT 10:03 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 449 POSTS
Backing plate.
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Monday, August 14th, 2023 AT 10:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
You should be able to access it there. Usually, they provide a plug for that reason. When you do it, adjust it until you feel a drag on the wheel. Then, pump the brakes a few times and recheck it. If the drag is gone, adjust a little more and repeat the process.

Let me know.

Joe
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Monday, August 14th, 2023 AT 10:46 PM
Tiny
JEFF HERMAN
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  • 449 POSTS
Impossible to get to unless there's a special tool.
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Monday, August 14th, 2023 AT 11:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

They make what is called a brake spoon. Is that what you are using? Are you able to see the adjuster with the plug removed?

Let me know. I attached a pic of the tool I'm referring to.

Take care,

Joe

See pic below.
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Tuesday, August 15th, 2023 AT 8:53 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 449 POSTS
I'm familiar with the tool, but you cannot see the adjuster through the hole. The brakes work very well so it's all good. This car I'm told won't see 3,000 miles in the next 5 years, lol. That would make it a Civic hatchback with 126,000 miles, circa 1995.
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Tuesday, August 15th, 2023 AT 8:58 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I agree with you. If they are working properly and that's all the miles it will be used, I would be happy with it the way it is.

Regardless, take care of yourself, and feel free to come back anytime in the future.

Joe
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Tuesday, August 15th, 2023 AT 9:30 PM

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