86Chev Caprice SW Master Cylinder Help Needed

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Old 12-06-06, 05:54 PM
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86Chev Caprice SW Master Cylinder Help Needed

I was driving home the other night and the brake light began flickering. I am sure that the master cylinder needs to be topped up, as that is how it was acting. But, when I popped open the top...there is a diaphram on top...not like my 86 Ford P/U master cylinder, which was open and I could see how much fluid it needed. The breaks worked, but the pedal was really low.

Also of note, we just thawed out of a really cold spell and that may have affected things, but prior to that, the brakes have been just fine, with no leaks etc.

Help! Do I need to take that diaphram off and fill? I am fairly car savvy but I have never seen one like this before, and do not want to damage anything.

I do need to drive the car, so I need to hopefully get this answered ASAP.

Thanks in advance...
 
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Old 12-06-06, 08:24 PM
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if I am understanding you, you removed the top of the master cyl and there is a rubber thingy left there, still over the fluid, close? it has sections that expand down intgo the resevoir as the fluid level goes down, right?

If so, it simply sounds like the seal for the master cyl stayed on the master cyl and didn't stay with the cap. simply remove the rubber seal and place it back into the cap. if it has the expandable section(s) you will need to push it (them) back to allow room for the added fluid.

brake fluid being low should not cause a low pedal unless it is so low as to allow air to enter the hydraulic system. If the pedal is suddenly low and the fluid is now low, I would look for some leaks somewhere.

When you fill the M/C pump up the pedal and hold it (with car running). It should stay high and (relatively) hard. If it drops, you probably have a leak to find.
 
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Old 12-06-06, 08:25 PM
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Nap,

THanks so very much, you hit the nail right on the head! The fluid was a bit low, but what I think happened, was when I originally took the cap off, I didn't get it properly seated again, and that was causing air leak/lack of vacuum...hence the the light and soft pedal.

At least I am praying that is the case, as I have to drive to work in the morning, in the dark with no one else to look at it til after work...go figure.

Here's hoping the situation is resolved, and thank you again for your prompt answer.
 
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Old 12-07-06, 05:00 AM
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I think you may need to do some detective work, Rhainy. Regardless of how you install the cap/cover on the master cylinder, it will not affect the brakes either in pedal feel or brake performance. You may have a bad master cylinder, which wouldn't be unthinkable in a 20 year old car; unless the fluid went low enough for it to suck air in ehich case it will need bleeding.
 
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Old 12-08-06, 05:50 AM
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Well, the situation isn't resolved so it is probably going to go to my mechanic because, as Tow Guy mentioned, it is probably a bad MC...*Sighing*

Brakes are still there but the pedal is low, even after adding some brake fluid, and the light is still flickering on and off when I press the pedal.

Thanks for all the help folks.
 
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Old 12-08-06, 09:24 AM
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If it's original, you probably got your money's worth out of it. I've got a couple of new brake rotors sitting in the garage waiting to go on my wrecker; figured 470,000+ miles was probably enough on the originals.
 
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