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bigpaulscars

Vacuum Booster

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I'm working on a 1955 EH fire truck. I rebuilt the master cylinder, bench bled it and bled the wheel cylinders. It has a hard pedal when the truck is off, once running the pedal goes to the floor and it has no brakes. It has what looks like a slave cylinder with hoses on a rod next to the master cylinder. Also another rod connected to the main brake rod running to what appears to be a vacuum canister.  I can not find any bleeders and it does not look like any other hydovac unit I have seen.  Any body have experience or suggestions to get the pedal back? Thanks in advance. 

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sounds like there is still lots of air still in the system   try bleeding wheel  cyls with wheels chocked and eng. running  add more b fl.as needed   as for the system don`t think i`ve seen such

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RE bleed the entire system. It may be a bad booster or a bad check valve. Does your booster look like this one? If it turns out to be the booster these peopel have the experence to do the early MACK systems.

Brake Materials and Parts Inc.

800 Sherman Blvd

Fort Wayne IN  46808

 260-426-3331

EMAIL: BrakePartsSTOP@aol.com

 

5a1a19400b7d0_AFTERREBUILTBRAKEBOOSTER-1949MackFireTruck.JPG.a91bf5309c72a7968d8ca3a631ed291e.JPG

Edited by 41chevy

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I'll post a picture of the booster. The engine does change when the brake in engaged so I'm inclined to think the booster is functioning. Did find a small leak in one line behind a clip. Replaced the line and will go back to bleeding the system again in the morning.  I appreciate the suggestions. 

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The booster is not connected to the hydraulic lines, it simply applied additional leverage to the pedal. The Master provides the only flow. I have flow to the wheel cylinders but not very strong. I have bled the system multiple times, a lot of air came out.  Pedal is very hard until it has assist from the vacuum, but either way the brakes are not engaging. It had some brakes before I started but fluid was pouting out the master cylinder, confused as to why it had no brakes but the leak is gone. 

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