# Brake booster/master problem



## GroundHog (Oct 16, 2009)

I just replaced my booster/master cylinder to a brand new unit from OPG (1970 GTO). After installing it a few months ago, everything was fine. Firm pedal, excellent stopping power. 

A couple weeks ago, i heard a pop from the booster/master area as i was driving around town and noticed the pedal was now able to be depressed a little further (a little mushier feel). The car still stopped fine, I didn't really feel that bad, almost felt like the pedal feel from the original so i thought nothing of it after checking the system visually. 

Went to drive the car today, and now all of a sudden the pedal goes all the way until it feels like the rod stops in the cylinder and i have no stopping power at all. Popped the cap off, and noticed the entire front reservoir was empty. Filled it up, still nothing. The entire time this has happened, there has been no leaks whatsoever. 

I'm at a loss here....new unit, bled properly, now not working at all without any leaks. 

Any ideas?


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## 05GTO (Oct 6, 2004)

Check *ALL* vacuum connections from manifold and carb,


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## GroundHog (Oct 16, 2009)

just checked, all connections are on and solid, no loose hoses. engine runs and idles great, also.


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## GroundHog (Oct 16, 2009)

The more I'm researching, the more it sounds like the master cylinder took a dump.

Never had one go out on me before, especially not a new one. does that sound like what is going on here?


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## Koppster (Jul 27, 2008)

Fluid had to go somewhere, have you a fresh bleed and then a test drive?


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## 05GTO (Oct 6, 2004)

Could be a bad check valve, check valve grommet or diaphragm, if you have a vacuum gauge test while the car is running at idle. Also check the rubber hoses on the front brakes, as Koppster the fluid had to go somewhere.


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## geeteeohguy (Feb 2, 2008)

Unbolt the master cylinder from the power booster and see if it's wet where the two meet. To me, it sounds like the master cyl. has blown a primary seal, and if it has, brake fluid will be going into the power booseter unit. Brake fluid does not dissappear: it leaks out, and has gone somewhere. Pull the wheels, check the wheel cylinders, calipers, hoses. If no leaks at the wheels, suspect the Master Cylinder. Don't just top it off and bleed it and drive the car. Something went Kablooey, and you lost fluid. Find out where it went!!!!


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## Rukee (Feb 8, 2007)

:agree with all the above statments, you need to find were the fluid went. Either there is a burst line or a bad wheel cyl somewere. But do not stop till you find where the fluid went.


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## GroundHog (Oct 16, 2009)

thanks for the info, guys. wheels and lines look good, so i'll try taking off the master cylinder this weekend.


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## daveh70 (Sep 4, 2008)

...on a similar note, I bought a new single circuit master cylinder (CBU200) "factory exact" from inline tube for my '64. Beware that no matter what they tell you, it will NOT work if your car as manual (not power) brakes. They told me it would work, but it doesn't. 

Anyone ever do a dual master conversion on their 64-66 GTOs? Any recommendations?


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## 66tempestGT (Nov 28, 2009)

daveh70 said:


> ...on a similar note, I bought a new single circuit master cylinder (CBU200) "factory exact" from inline tube for my '64. Beware that no matter what they tell you, it will NOT work if your car as manual (not power) brakes. They told me it would work, but it doesn't.
> 
> Anyone ever do a dual master conversion on their 64-66 GTOs? Any recommendations?


just bought a dual to replace my single on my 66. havent used it yet. got it from inline. my car is power. should have it operating in a week or two.


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## GroundHog (Oct 16, 2009)

Thanks geeteeohguy, that most likely sounds like what happened from what people have told me. I picked up another new master, I'll be pulling the old one off tonight to check it and probably replace it. 

If that is what happened and there is fluid in the booster, does that mean I need a new booster too?


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## GroundHog (Oct 16, 2009)

Pulled and inspected the master, everything is operational with no leaks. 

Found some fluid on the left front caliper, I'm guessing the newly found brake pressure popped the hose and/or bleeder valve. Replacing both of those this weekend, then replacing the caliper if the leak is still there.


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## faze07hd (Jul 2, 2010)

I hope you found your leak. If not, someone mentioned before that the fluid could have gone into the booster... This is a common problem and a good possibility... If you cannot find the leak, take off the master and remove the booster and twist it open. Pretty much anyone can do that. If you open it up and there is even an ounce of brake fluid, you must have it rebuilt. Also, that means that your master cylinder is no good and you will need a new one. Good luck.

Any questions, feel free to pm me.


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