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Intermitant Hard Brake Pedal; Even w/ many new parts
Topic Started: Mar 30 2012, 03:23 AM (1,317 Views)
Fabio421
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Hello all. This is my first post. I have a 1997 Geo Metro LSI w/ 263,000 miles. It is my wifes daily driver and she started complaining that the brakes would sometimes not work properly if she had been in stop and go traffic for awhile. At first I thought she was crazy becasue I drove it and the brakes felt fine. I couldn't get the problem to surface while I was driving it.

First I replaced the front pads and all of the fluid in the brake system. I figured that it was the original fluid and that it wouldn't hurt to change it. It didn't make a difference, she still had the problem. I then tested the check valve going into the brake booster. It tested out "Good". I took the other hose off that goes from the intake manifold to the hard line that runs along the firewall and eventually to the other rubber line, check valve and booster. It had what appeared to be carbon inside of it. The reason I say "appeared to be carbon" is because it looked like baked carbon but I suppose it could have been some plastic piece at some point in it's life. Any idea? Anyway, this "carbon" was partially blocking this hose so I cleaned it out of the hose. I then ran all of the tests on the brake booster. It passed all tests with flying colors. So I took the car and made a big circle around town and just kept driving it and doing alot of panic stop braking to get it to mess up. After about 40 minutes of this it did. The best way I can describe it is that the pedal was firm but the car wasn't stopping as quickly as it normally would. It kind of felt like an old car with wet drum brakes if any of you know that feeling. Anyway, the brake problem manifested itself while I was driving and I was able to get it to repeat this problem multiple times. I also noticed that when I did a hard stop and took my hands off the wheel, the car would pull slightly to the left. I immediately drove home and took a temp reading of each front caliper. The drivers side caliper was about 100 degrees F hotter than the passenger side. The drivers side wheel had also been dusting alot worse than the passenger side. I thought that either the drivers side was sticking, causing it to dust more and to get hot or that the passenger side wasn't engaging enough and was causing the drivers side to do more of the braking. I bought two new front calipers and installed them. Upon driving the car, my wife reported that the problem persisted. I had done some searching here on this forum and found a thread where someone had a similar problem and it was reported to be a bad brake hose. The brake hose was swelling and coming apart on the inside and was restricting the return flow of fluid, causing the caliper to drag. It sounded like it was a possibility so I ordered two new front brake lines and changed them. The problem remained. I was really banging my head against the wall at this point and asking my friends whet their opinion was of the problem. Without fail, I kept getting the same response, "the brake booster is bad". My retort was always " well OK, explain to me how it can only be bad sometimes. Wouldn't a bad booster result in weak brakes all the time. They all said that it would but they were sure it was the booster, even though it had tested as good. At this point I was out of ideas so I ordered a new booster from NAPA. It came in and I replaced the booster with the new one. While installing I paid attention to the master cylinder. It had not been leaking into the booster at all. It was dry. So I finished installing the booster and bled everything again. My wife drove the car for a few days and the problem surfaced again. :smackface :banghead What the hell did I miss? There isn't much left in the braking system. I feel like a chump for replacing all of these parts and not having fixed it but I just keep telling myself that this is a safety issue and that the brake system is now more robust and therefore safer for my beloved wife. It's a good thing that Geo Metro parts are inexpensive. Otherwise I might have a different opinion of the darn thing.

Any help you can offer is greatly appreciated :cheers

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Woodie
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It's that hose or the valve that is either in the middle of the hose, or where the hose connects to the booster.
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JellyBeanDriver
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Nevermind - I replied without fully reading your post.

Will have to think about it. You already took care of the hose at the manifold which is where my problem was but I do suggest you replace it. It's falling apart already. Check your local auto parts store for the hoses they sell by the foot and buy the correct size but the one with the stiffest sidewalls.
Edited by JellyBeanDriver, Mar 30 2012, 09:46 AM.
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Geo Glenn
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What's in your engine?

Your problem is in the fluid return check valve inside the master cylinder. Replace the master cylinder and the problem will disappear.
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Fabio421
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Geo Glenn
Mar 30 2012, 09:51 AM
Your problem is in the fluid return check valve inside the master cylinder. Replace the master cylinder and the problem will disappear.
You sound very sure of this. Since it's the only majot component I haven't replaced I'd probably have to agree. Can you elaborate a little more? Thanks
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Spock
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Live Long and Prosper.

Rather than simply cleaning out the brake booster hose, I'd recommend that you just break down and replace it.

Did your hose look like this?

Posted Image

I can't be certain, but if I was a betting man I'd say that they used some very cheap hose in these high dollar, performance oriented
Geo Metros :D
Mine was doing the same thing that you (and your wife) are describing. I replaced the hose and from the looks of things,
the cheap hose had just collapsed and failed on the inside.

I'd go down that road first because it's the cheapest option, then if that doesn't fix the problem, your master cylinder is
the only remaining suspect.

Good Luck,

Spock
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Scoobs
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Decal Vendor

I got a couple spare brake boosters :p
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Woodie
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Spock
Mar 31 2012, 04:07 PM


I can't be certain, but if I was a betting man I'd say that they used some very cheap hose in these high dollar, performance oriented
Geo Metros :D
Mine was doing the same thing that you (and your wife) are describing. I replaced the hose and from the looks of things,
the cheap hose had just collapsed and failed on the inside.

No question they cheaped out on this item, it collapses after a mere twenty years or so :P Actually, My first Metro did this after just seven years, but 215K miles, I've seen it many times.
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Geo Glenn
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What's in your engine?

Fabio421
Mar 31 2012, 12:22 PM
Geo Glenn
Mar 30 2012, 09:51 AM
Your problem is in the fluid return check valve inside the master cylinder. Replace the master cylinder and the problem will disappear.
You sound very sure of this. Since it's the only majot component I haven't replaced I'd probably have to agree. Can you elaborate a little more? Thanks
The symptoms match my diagnosis. As the brake fluid gets hot when the brakes are applied, the fluid expands. Brake system design allows the excess pressure from the expanded fluid to relieve through the master cylinder. When the pressure relief valve in the master cylinder gets clogged or stuck, the brakes stick, especially the front brakes.
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Woodie
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That would cause the brakes to stick ON. I see no way that this would cause the pedal to go hard. A clogged or collapsing vacuum line does this exact thing. Brakes work perfectly unless you get into a stop and go traffic situation where you're applying the brakes multiple times in quick succession. The engine can't suck enough vacuum through the clogged hose in a short time.
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JellyBeanDriver
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Woodie
Apr 1 2012, 04:06 AM
No question they cheaped out on this item, it collapses after a mere twenty years or so :P Actually, My first Metro did this after just seven years, but 215K miles, I've seen it many times.
I wish it was more commonly known back when I had the problem, but I am glad to finally solve it.


I think with TBI and the way it's plumbed in, raw fuel can get to that hose and over the years eat away at it/make it deteriorate. Maybe when the engine is shut down. It always happens right after the metal nipple ends in the hose.
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Woodie
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I figured it out after totalling the car. Well, about $1000 damage, but with 215K miles on it, we decided to just get a new one. I kept telling my boss that the brakes just didn't work once in a while, he kept telling me they were fine. After the wreck I pulled off the vacuum hose and showed it to him, he begrudgingly admitted that maybe that might have done it. I've seen it many times since then.
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Fabio421
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Well, I took the advice of Geo Glenn ( because these other responses hadn't been posted yet ) and I can safely say that he was incorrect. The master cyl. made no difference at all. The hose theory makes send if it is collapsing. The carbon build up inside of it isn't the problem because I cleaned that out at the beginning of this epic journey. I probably have the only Geo Metro in North America with new calipers, hoses, fluid, pads, booster and master cylinder. My wifes getting a new car one part at a time. LOL

I'm off to buy some vacuum hose. Wish me luck.
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Coche Blanco
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Troll Certified

"I probably have the only Geo Metro in North America with new calipers, hoses, fluid, pads, booster and master cylinder".

You'd be surprised. haha
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Geo Glenn
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What's in your engine?

Fixing Geo Metros over the internet is hard sometimes . . . :hmm
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