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1985 Eldorado Biarritz Convertible, Sable Black, HT4100
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1,000 Posts
Discussion Starter #1
Hi guys,
Recently I blew a brake line, had it replaced along with the master cylinder, which was not working 100%. I don't drive my car very often, maybe twice a week. Last week I noticed some excessive travel in the pedal while driving, which seemed to correct itself, then when parked and running, a sucking sound from the firewall when pressing the pedal. Figured it was air in the line and was about to get them bled, but I noticed today that the fluid in the rear half of the new MC is at about 80%, while the front half is full. I'm worried the new MC — which was a no-name brand, the only brand the garage could get from their supplier — has already failed and is leaking fluid into the booster. Booster never had any leaks, etc before. No leaking fluid visible around the MC or booster, or between them. No leaks visible elsewhere in the brake lines.

My biggest concern right now is sucking brake fluid into the vacuum and screwing more up. I went to check the hose for fluid but the check valve feels so fragile I'm afraid to pull the hose off it. Is the proper way to do that to just pull the valve out of the booster with the hose still on it?

Should I also do regular booster checks at the pedal, or is the low fluid without a leak sufficiently indicative of a blown MC leaking into the booster?

If fluid did get into the booster, does it need to be replaced?

Thanks a lot,
Scott
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,265 Posts
Hi guys,
Recently I blew a brake line, had it replaced along with the master cylinder, which was not working 100%. I don't drive my car very often, maybe twice a week. Last week I noticed some excessive travel in the pedal while driving, which seemed to correct itself, then when parked and running, a sucking sound from the firewall when pressing the pedal. Figured it was air in the line and was about to get them bled, but I noticed today that the fluid in the rear half of the new MC is at about 80%, while the front half is full. I'm worried the new MC — which was a no-name brand, the only brand the garage could get from their supplier — has already failed and is leaking fluid into the booster. Booster never had any leaks, etc before. No leaking fluid visible around the MC or booster, or between them. No leaks visible elsewhere in the brake lines.

My biggest concern right now is sucking brake fluid into the vacuum and screwing more up. I went to check the hose for fluid but the check valve feels so fragile I'm afraid to pull the hose off it. Is the proper way to do that to just pull the valve out of the booster with the hose still on it?

Should I also do regular booster checks at the pedal, or is the low fluid without a leak sufficiently indicative of a blown MC leaking into the booster?

If fluid did get into the booster, does it need to be replaced?

Thanks a lot,
Scott
======================
I'm worried the new MC — which was a no-name brand,
the only brand the garage could get from their supplier —
has already failed and is leaking fluid into the booster.

I assume it has a warranty from the installing shop -
take it back and let them check it out -
you already paid for it -

My biggest concern right now is sucking brake fluid into the vacuum and screwing more up.
can't imagine HOW brake fluid could possiby get sucked into the vacuum -

the vacuum booster simply assists applying the brake pedal -
 

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1985 Eldorado Biarritz Convertible, Sable Black, HT4100
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1,000 Posts
Discussion Starter #3
Thanks Basscatt. I figured if the vacuum pulls in gas from the booster, it would pull in liquid too if present in the booster.

Yes, it should be under warranty by the installing shop. Not that I'd want them to install another one of those P.O.S. MCs. Unfortunately, that shop is about 20 miles away. I blew the brake line while visiting family in the suburbs and had to go to the nearest garage. I'm worried about driving there with a failing booster and failing MC. Internet research tells me my booster diaphragm is living on borrowed time if it hasn't already ruptured due to exposure to brake fluid. That correct?
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,737 Posts
Are you a mechanic? If so, simply unbolt the master cyl. from the booster and gently pull it away, lines left attached. Is it wet behind the master cyl. If so, you have a defective master. "blew a brake line"? do you mean a rubber flex hose or a steel line? What is common on these cars is failure to use the parking brake EVERY time the car is parked. If not used, the pistons within the rear calipers do not rotate. Not rotating causes them to seize within the caliper. That then increases brake pedal travel. Sitting still, the parking brake should hold the car from moving in gear. Depress the parking brake and brake pedal hard with both feet at the same time, then gently lift your foot off the regular brake pedal. Does the car squat and remain at rest? If it creeps forward, your rear brakes aren't working! Rarely can it be fixed except for replacement of new rear calipers and then having them adjusted by the Factory service manual which I presume you have?
 

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1985 Eldorado Biarritz Convertible, Sable Black, HT4100
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1,000 Posts
Discussion Starter #5
Thanks, Carnut. Am I a mechanic? No. But I have wrenches and I can unbolt things.

To clarify, I blew a steel brake pipe at the right rear caliper, the pipe between the caliper and the hose. After replacing the rear calipers a few months ago, I religiously engage the parking brake.

If I unbolt the MC and pull it away and find fluid, is it drivable? And will I need a new booster if the booster diaphragm was exposed to brake fluid?
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,737 Posts
Drivable??? If you mean to the repair shop, no. If it's wet then the master is leaking. And leaving it disconnected proves it's leaking to the shop owner. Have it towed and if you don't have towing insurance ask the repair shop what tow service they use. That way they can absorb the tow if warranted. If it's dry, then bleed the system. The rear half close to the booster is front brakes, the one further away is rear brakes. Regarding brake fluid damaging the booster, I think you'll get multiple answers. In my 40 years, I've never replaced a booster for brake fluid entry.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,265 Posts
Drivable??? If you mean to the repair shop, no. If it's wet then the master is leaking. And leaving it disconnected proves it's leaking to the shop owner. Have it towed and if you don't have towing insurance ask the repair shop what tow service they use. That way they can absorb the tow if warranted. If it's dry, then bleed the system. The rear half close to the booster is front brakes, the one further away is rear brakes. Regarding brake fluid damaging the booster, I think you'll get multiple answers. In my 40 years, I've never replaced a booster for brake fluid entry.
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In my 40 years, I've never replaced a booster for brake fluid entry.
---------------------------:yeah:
and you can add my 40 years to that -
NEVER experienced brake fluid getting into a booster -
there is simply no hydraulic connection between the two parts -
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,737 Posts
Yes there is! Brake fluid can travel up the master cyl. push rod and drip into the booster if the rear seal on the master fails. The argument is that the fluid can damage the booster diaphragm. I would like to see proof.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,265 Posts
Yes there is! Brake fluid can travel up the master cyl. push rod and drip into the booster if the rear seal on the master fails. The argument is that the fluid can damage the booster diaphragm. I would like to see proof.
=============================
I've seen plenty of leaky masters dripping brake fluid all over the front of the booster -
but can't remember ever seeing fluid inside the booster - :hmm:

but - if we simply change the question slightly and ask -
can exposure to brake fluid damage the diaphragm within the power booster -
that answer is NO -

--------------------

over the years I have seen damage to rubber brake parts
from almost every fluid used in a car -
the worst was trans fluid or power steering fluid -

the BEST explanation was -
"oh - it was really low - and that's all I had" -
 

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1985 Eldorado Biarritz Convertible, Sable Black, HT4100
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1,000 Posts
Discussion Starter #10
Thanks again Carnut and Basscatt. Good news. I took my Eldo back to the garage that installed the newer master cylinder. They pulled the MC off and checked it for leaks at the booster and found none. They took photos and showed me. Said they also checked the booster for a vacuum leak and found none. No leaks from the brake lines that would explain a quick drop in brake fluid, so they re-bled them in case their last bleed left air in them. That seems to have solved it. No charge. Brakes seem fine now. They said the recent bleed did remove some air but not a lot.

I knew that air in the lines would make them spongy, but could that explain the sucking noise too?
 

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1985 Eldorado Biarritz Convertible, Sable Black, HT4100
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Discussion Starter #12
Update: My brakes got spongy and weak again after a month or two and the Brake warning light came on permanently. My regular mechanic took a look and said when he unscrewed the brake line at the master cyl. it leaked noticeable air before fluid. He guessed the no-name brand master cylinder the other shop installed was junk and putting air in the lines somehow. He didn't think it was a bad bench bleed, as I'd guessed, because the brakes worked well for a while, then gradually got worse. Makes sense. I only got that no-name MC b/c I was in a pinch—other shop told me my MC was dangerously close to failure and that was the only MC they could get from their supplier. I believe he told me the brand was "PRD", I think. Can't even find it online. New ACDelco installed yesterday, warning light now off, brakes good again. Another lesson learned.
 
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