what exactly seals the power brake booster to the master cylinder? - Team Camaro Tech
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post #1 of 13 (permalink) Old May 18th, 08, 10:37 AM Thread Starter
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what exactly seals the power brake booster to the master cylinder?

what seals the booster to the master on a 69 camaro. I installed a rebuilt original booster and master on my car. before the install my brakes were fine.Long story short my booster will not build or hold vacuum. I have come to the conclusion that I either have a bad booster or I am missing something where the master bolts to the booster. I know the push rod has an o ring on it, is there any other seals? a gasket between the master and the booster? how about on the end of the master that goes into the booster . does that round shaft get an o ring in the groove?? going crazy. thanks in advance.


ps I saw that dave pozzi is big into this type stuff, dave, if you could reply that would be great.
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post #2 of 13 (permalink) Old May 18th, 08, 11:03 AM
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Re: what exactly seals the power brake booster to the master cylinder

O ring in the groove,

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Last edited by 68Lemans blue; May 18th, 08 at 11:53 AM. Reason: :) fat fingers
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post #3 of 13 (permalink) Old May 18th, 08, 11:56 AM Thread Starter
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Re: what exactly seals the power brake booster to the master cylinder

thanks jerome, now so I know I have this right. i have an o ring on the 4" push rod that goes from the booster into the back of the master. o ring end into the booster. ok also at the back of the master there is a shaft about an inch or so in diameter with a pretty big grove in it, are you saying this groove also gets an o ring? Boy I hope thats what you are saying, I took my old stuff off as 1 piece and installed my new stuff with out anything in this groove. thanks again
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post #4 of 13 (permalink) Old May 18th, 08, 02:13 PM
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Re: what exactly seals the power brake booster to the master cylinder

The rear shaft has no o ring. Air needs to enter the rear to operate the booster. The groove is for a retainer which holds a felt pad of sorts that filters air entering. It also muffles air flow or the booster can make a gasp sound.

The master cyl side of the booster should have a rubber cup type seal.

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post #5 of 13 (permalink) Old May 18th, 08, 02:38 PM Thread Starter
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Re: what exactly seals the power brake booster to the master cylinder

thanks dave, I believe you are talking about the drivers compartment side of the booster. I was wondering if any type ring went around the grooved shaft on the rear of the master which actually goes over the rubber cup type seal in the booster. I also have a few other questions: my car has front disk, is the 4" push rod right? or do I need a shorter one? any gasket between the master and the booster. thanks
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post #6 of 13 (permalink) Old May 18th, 08, 04:49 PM
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Re: what exactly seals the power brake booster to the master cylinder


Just the small O ring on the end.

A deep hole master cyl uses the long rod, a shallow hole master uses the short rod. The rod should not push on the master cyl piston when bolted up. The clearance is .010" to .015" this allows full piston return to prevent dragging brakes.
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post #7 of 13 (permalink) Old May 18th, 08, 05:00 PM Thread Starter
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Re: what exactly seals the power brake booster to the master cylinder

thanks dave and I am sorry for crossing you up. I have everything set up as you say. I can not build or hold any vacuum. is there any gaskets, seals etc.. at all that go between the master cylinder and the power booster. i seem to think I am missing something. On the back of the master there is a round end pretruding out with a groove in it. does this get a seal? is there a gasket between the flange where the master bolts up and the booster? thanks again
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post #8 of 13 (permalink) Old May 19th, 08, 03:27 AM
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Re: what exactly seals the power brake booster to the master cylinder

Quote:
Originally Posted by L7869 View Post
is there a gasket between the flange where the master bolts up and the booster?
A rubber cup seal in the booster seals against the end of the master cylinder. Check for cuts in the seal.

Use petro jelly for lube, the groove should not be at the same depth as the rubber seal. You could make a paper gasket, but the rubber seal has being doing good for quite some time.

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post #9 of 13 (permalink) Old May 19th, 08, 05:09 AM
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Re: what exactly seals the power brake booster to the master cylinder

Quote:
Originally Posted by davidpozzi View Post

Just the small O ring on the end. The other grooves are for ID.

A deep hole master cyl uses the long rod, a shallow hole master uses the short rod. The rod should not push on the master cyl piston when bolted up. The clearance is .010" to .015" this allows full piston return to prevent dragging brakes.
David


L7869, I hope we were talking the same rod , as David posted ,I should of been more in detail, but yes this rod ,Hope alls working for you ,Sorry it was at the end of lunch .

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post #10 of 13 (permalink) Old Jul 23rd, 08, 08:50 AM
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Re: what exactly seals the power brake booster to the master cylinder

I hope its not too late to join this conversation...I have a similar problem with the power brake booster on my '69 Camaro. I cannot retain the vacuum. There is a noticeable hissing sound coming from the bottom of where the master cylinder mates with the booster. When I stuff a rag in the area, the hissing stops. It also stops when I pinch off the vacuum line to the booster. I disassembled the master cylinder from the booster and the cup gasket seems to be ok. I noticed a vertical indentation or groove at the bottom of the shaft hole in the front face of the booster that seems to be allowing air into the booster. Is this the makeup air that David was referring to in his May 18 posting? If so, any other thoughts on why the booster is not holding vacuum? Thanks for your help...
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post #11 of 13 (permalink) Old Jul 23rd, 08, 07:07 PM
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Re: what exactly seals the power brake booster to the master cylinder

The end connected to the pedal needs atmospheric air to enter in order to make boost. The push rod from the pedal opens a "reaction valve" inside and permits the air to enter. The master cyl end has the removable push rod and it is sealed by a cup shaped seal. The rear of the master cyl needs to be vented to allow any leaking fluid to run out and not into the cup seal where it would damage it.

Any leaking of the cup seal would cause a loss of vacuum.
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post #12 of 13 (permalink) Old Jul 24th, 08, 03:26 PM
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Re: what exactly seals the power brake booster to the master cylinder

David - Thanks for your input and information. Upon closer examination of the master cylinder, I found what appears to be a small pinhole in the casting of the mounting flange near the mating surface of the rear of the master cylinder to the front of the booster. A considerable amount of air was being sucked into the hole. I plugged the hole with silicone and now the brakes worked as advertised. Thanks again!
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post #13 of 13 (permalink) Old Jul 25th, 08, 10:17 AM
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Re: what exactly seals the power brake booster to the master cylinder

Glad you found it, I would have used epoxy glue on it.
David

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