Stuck in diagnosis: Temporary loss of brakes

[Bryan]

1999 Honda Civic LX
no ABS
Front disc, rear drums
198,000 miles, Ohio

Quick summary:
I’m stuck in my “loss of brakes” diagnosis after doing several checks. I experienced loss of brakes 15 minutes into my normal work commute (thankfully with little traffic). The brake pedal went down to the floor. I rode my E-Brake back home, but to my surprise later that same day the brakes seemed to work normal again. Help from somebody that has experienced this type of situation would be greatly appreciated! Thanks!

I have done many tests (see below) and cannot find out the cause. Both the Brake Master Cylinder and Brake Booster don’t sound like the issue to me. Could a small piece of debris or air bubble cause the temporary loss of brakes?

Tests:
-No loss of brake fluid after pumping brakes countless number of times.
-No evidence of fluid leaks at lines, hoses, front calipers, rear drum cylinders. 
-Brakes apply at all 4 tires. I tested with car on jack stands and spun tires while my wife applied brakes.
-Pedal does NOT slowly sink to floor with and without the car running.
-Passed the “Functional Test” and “Leak Test” described in Honda Service Manual (SEE IMAGE ATTACHED). I did not test Brake Booster for vacuum.

I’ve since driven the Civic again for 15 minutes around the neighborhood and the brakes still work fine.

Attachments:

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Topic

[RedneckRickem]

The fluid itself seems to be the problem, had a similar problem with another older accord. The fluid had never been flushed and my guess between the hydraulic breakdown of the fluid and moisture caused brake failure. I flushed the system (bleed the brakes) at all four corners and have never got a call back, so either the guy died in a horrific brake failure crash or it solved the problem, LOL

[Bryan]

Thanks for the info. So I’ve actually last flushed the brake fluid at all 4 wheels and replaced with Genuine Honda brake fluid two years ago.

Any ideas on how moisture can get into the lines/fluid?

[David]

brake fluid is very hygroscopic – it absorbs it from the air, and you will have moisture make it’s way past the seals in the calipers/wheel cylinders. (that’s why the brake fluid in the reservoir changes color with time (if you live in a climate where there is rain/humidity) – when you bleed the brakes, if you watch the fluid that first comes out, it will be much darker than the fluid that follows it.

Generally, water in the fluid does two things – it makes the brake fluid more corrosive (damage to the inside of the caliper/wheel cylinders) and it drops the boiling point of the fluid.

Not a bad idea to flush it every other year, at least. Any quality brake fluid (Dot 3,4, or 5.1 – not dot 5) will be fine.

Not sure what caused the failure – going to the floor generally means the system isn’t holding pressure – could have been an issue with the seal in the master – maybe a piece of debris? I’d start with flushing the fluid with fresh fluid, just to be on the safe side – watch carefully for any crud. (unfortunately, if there is corrosion, and you aren’t leaking, you might not know about it until you replace the pads and push the cylinders back)

[Mike]

A brake pedal that suddenly drops to the floor when applied, in the absence of leaks, is typically a failing master cylinder.
Your master cylinder has seen 18 years and 198.000 miles of use. Not unusual for it to be wearing out.

Brake fluid that’s only 2 years old, is highly unlikely to have absorbed enough water in 2 years to boil and caused a sudden, temporary brake failure.

If it was my car, I would buy a brand new master cylinder—not rebuilt or remanufactured, as those are more trouble than they’re worth.
My shop would never install rebuilt unless there was absolutely no alternative.

Beck Arnley and Centric Premium have always been reliable in my experience.

[Mike]

[quote=”DrD” post=189930]brake fluid is very hygroscopic – it absorbs it from the air, and you will have moisture make it’s way past the seals in the calipers/wheel cylinders. That’s why the brake fluid in the reservoir changes color with time (if you live in a climate where there is rain/humidity) – when you bleed the brakes, if you watch the fluid that first comes out, it will be much darker than the fluid that follows it.[/quote]

To be honest, a lot of the darkening you see in old brake fluid is due to microscope rubber particles suspended in the fluid. Obviously, these particles get sloughed off the various wetted rubber seals and lines within the brake system over time.

[Bryan]

I really appreciate everybody’s comments on my car’s issue!

I had done nothing out of the ordinary. This brake loss event was purely random and during my normal commute. As Bonnieman mentioned, no recent brake work to introduce air into the lines (I last did brake work by replacing the drums two years ago as well as replacing brake fluid that same day).

I’m going ahead and ordering a new master cylinder to be on the safe side (thank you Bonnieman for recommended brands). I think they’re around $60-$80 online. It is strange though as I would think a failing master cylinder would permanently not work again, not temporary as in my case. But this is why I’m leaning on all of your experiences 🙂

I’ll be sure to update this thread at some point after I replace the master cylinder. Thanks again everyone!

[David]

I pumped my brakes and it worked until I came to a red light and slammed my brakes. One tire locked up the others didn’t so the car slid sideways. Very scary. Turned out it was the master cylinder, so it’s very important.

[Author]

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