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| power brake troubles https://slantsix.org/forum/viewtopic.php?t=12855 |
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| Author: | 225dart [ Tue May 03, 2005 7:43 pm ] |
| Post subject: | power brake troubles |
hope someone can help. i am/was in the process of converting my slant six dart to power brakes. all was going well, untill i started the car first thing i noticed, was the still rock hard pedal. second thing i noticed, pedal did not return to "at rest" position---it stayed pretty much down, thus causing the brakes to drag. if you put your foot behind the pedal and pull up, the brakes release. needless to say the manifold vacum is definetaly pulling hard on the diaphram of the booster. i dont happen to have my service manual nearby---actually, im not sure where i put it. i did find an 85 diplomat service manual, and best i can tell from that, the booster is no good as one of the tests says i should see no more than 12" of vacum at the check valve, i have 14-15" of vacum. also, when you start the car, it pulls the pedal about 1/3-1/2 way down instantly. notsure why it does this either. any ideas here? im at a loss. these boosters are supposed to be simple right? just a giant vacum cannister. --chad |
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| Author: | Jeb [ Wed May 04, 2005 2:04 pm ] |
| Post subject: | |
Master cylinder and proportioning valve are different for power and manual brake setups. You did change those two did'nt you. Push rod on the booster could also need a little fine tuning. |
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| Author: | SlantSixDan [ Wed May 04, 2005 2:45 pm ] |
| Post subject: | |
Quote: Master cylinder and proportioning valve are different for power and manual brake setups. You did change those two did'nt you.
No, the prop valve is not different for power vs. nonpower brakes—the difference in prop valves is disc or drum front brakes for any given model year of any different chassis type (A-body, B-body, etc.), and there are differences among different years when the brake systems changed.Master cylinders are of different bore diameter for power or nonpower in some systems in some years, not in others, and the difference in bore diameter doesn't cause the symptoms the OP mentions. Quote: Push rod on the booster could also need a little fine tuning.
This is likely where the OP's trouble lies. Also, depending on what booster/linkage setup he used, he may wind up having to shim the booster bracket away from the firewall and/or redrill the brake pedal arm to set everything right.
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| Author: | Guest [ Thu May 05, 2005 4:08 pm ] |
| Post subject: | |
but its all a stock a-body setup, so why would i have to shim/drill things? and why when you start the engine does it pull so much vacum on the booster that it drags the brakes? from what i can see in the service manuals, and tests i have performed, it appears the booster itself for whatever reason is bad. now, to find a good one somewhere............... --chad |
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| Author: | SlantSixDan [ Thu May 05, 2005 4:15 pm ] |
| Post subject: | |
Quote: but its all a stock a-body setup, so why would i have to shim/drill things?
Because there are lots of "stock A-body setups", many of which do not simply bolt onto whatever A-body and behind whatever master cylinder you happen to have. What's more, even if you have all the components that are correct for your year and your master cylinder, there are adjustments and settings that need to be set up correctly, otherwise the system won't work.Quote: and why when you start the engine does it pull so much vacum on the booster that it drags the brakes?
The engine is supposed to pull "so much vacuum" on the booster. That's the way power brakes work. Your brakes drag on engine startupbecause something's not adjusted or spaced correctly. Remember, with power brakes, the brake pedal becomes basically an activation switch, which causes the booster to apply pressure to the master cylinder, activating the brakes. In your case, the booster "thinks" the pedal is pressed down when it's really not. So, you need to go through all the setup and adjustment procedures shown in the factory service manual applicable to your-year, your-model, your-brake-system. If you're starting from zero knowledge, trying to use an inapplicable manual (you mentioned an '85 Diplomat manual...TOTALLY different system!). |
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