Sudden loss of brake pedal pressure

[m3x1c0]

Anyone know why I might lose pressure in the brake pedal. Car looks like it's been switched to a standard vacuum setup. No apparent leaks, vacuum line looks good. What should I look for?

 

[TexasT]

Master cylinder leaking internaly. Does it go down slowly? How old is the mc? If you let up on the pedal does it come back up and lose pressure again? If so, probably time for another one.

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[m3x1c0]

There is some leak from behind mc against vacuum booster. Pedal has pressure if I pump while engine is off. Engine on and it goes to the floor

 

[TexasT]

If it is leaking brake fluid I would replace it.

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[Chuck Leeper]

If it's leaking at the rear of the MC, you can expect the fluid to be in the booster, too. The fluid will kill the diaphragm.

 

[m3x1c0]

What parts will interchange? car is in the shop right now can't find a part.

 

[TexasT]

Might have to take the mc off and down to the part house to match something up. I'd start with something for a g body.

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[turbofrank]

start with 86-84 Cutlass

 

[m3x1c0]

Gonna use an 87 N/A Regal MC. per Rick's suggestion (turboburick). which happens to have the same part number as off of a Monte Carlo at auto zone

 

[m3x1c0]

Wow! there was no rod inside the booster! (the one that pushes into the MC) looks like it might have broken off and fell in. Probably needs a new booster now as well holy crap how did it brake at all?

 

[m3x1c0]

Wow! there was no rod inside the booster! looks like it might have broken off and fell in. Probably needs a new booster now as well holy crap how did it brake at all?

-- haha pun not intended by the way, but also how did it break? --

 

[m3x1c0]

okay nevermind. Not sure if there is a rod that goes there. The shop is going to take a look at the proportioning valve. Also, the car started losing coolant so looks like it needs a water pump too... when it rains, it pours.

 

[m3x1c0]

okay so, new MC installed and still no pedal (yes the brakes were bled) looking at the proportioning valve next. Can anyone identify the one on the car? I'm assuming its either stock or from a standard regal:

can it be rebuilt?

 

[TexasT]

Did you bleed the mc? Is is spongy or just drops to the floor? Reman mc or new? Could be a bad reman mc. Do you have a known good that could be swapped on temp to see?

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[m3x1c0]

Did you bleed the mc? Is is spongy or just drops to the floor? Reman mc or new? Could be a bad reman mc. Do you have a known good that could be swapped on temp to see?

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yep bench bled. Brand new MC. No we don't have a good one. Cleaning out the proportioning valve and reinstalling everything once more to see what happens. We may end up swapping to another MC to see if its a manufacturing defect. Current one showers inside the reservoir like a bad seal or something.

 

[m3x1c0]

Fixed! Took apart the prop valve, cleaned it the best I could, put everything together and it all works again! I'm guessing something from the broken mc got caught in there. Not sure, but it works now!

 

[BARRACUDA1968]

Good to hear just be careful for a while.

 

[m3x1c0]

Good to hear just be careful for a while.

Oh I will, I was rushing to get it done because the car was supposed to appear in a small show tonight but unfortunately Gbodyparts didn't get me my new bumper in time anyway. Guess Ill go in my Mustang :/

 

[BARRACUDA1968]

I've been without my GN all summer, lost the bearings first drive out this spring. I'm in Iowa so it was a long winter and now becoming a long summer. I bought my car last July so I didn't really get the new wore off before I had to put it away for winter. I'm like a child on Christmas Eve but every morning I wake up it's still Christmas Eve.

Waiting to get my motor back.

 

[m3x1c0]

I've been without my GN all summer, lost the bearings first drive out this spring. I'm in Iowa so it was a long winter and now becoming a long summer. I bought my car last July so I didn't really get the new wore off before I had to put it away for winter. I'm like a child on Christmas Eve but every morning I wake up it's still Christmas Eve.

Man that sucks! I've contemplated keeping an extra long block around just in case. but thats probably a little excessive, lol. I see in your sig yours is a stroker. Is it being fixed or are you going to build a new one?