'57 F-600 Brake Booster

[john connell]

I love my old girl having owned it for about 5 years. She's all original and runs quite well with the 292 V8 with 4 barrel carb and 5 speed hi/lo transmission. Problem is that
I can't trust her to stop without extreme effort. I'm certain the individual drum brakes all need adjusting but my biggest problem is the lack of cooperation I get from my vacuum booster. It's located beneath the seat and when it operates, my thought is that the attached slave valve sends fluid to all 4 brakes. I bled the entire system a month ago hoping for better results but instead got different, not better, results. Now my brake pedal takes about three feet of travel to the floor before feeling braking action then the second pump is only about 2 feet of travel and around the 3rd or 4th pump I often times can get her stopped that is if I don't have a big load on her. The booster does have good vacuum hose to it and sounds like air brakes releasing on a semi tractor but the action is horrible. I do have a parts truck with the same device but don't know anything about their operation. Do you? Sure would appreciate your advice. John

 

[Tom in Mo.]

Sounds like two different issues. The long pedal pumping is air in the line somewhere, it only takes a tiny bubble to be mushy. The booster business sounds like a job for a heavy truck shop to look at. Those guys can probably sort that out in a jiffy.

 

[john connell]

I appreciate your thought, Tom. I think I agree with both and have looked further into the setup of the hydraulics. I intend to investigate the operation of the master cylinder on the firewall and the resulting action of the slave valve on the booster mounted on the lower frame. I wonder if both them shouldn't be rebuilt assuring that the seals inside don't allow reduced pressure and ineffective operation of the booster. Thanks Tom.

 

[Longknife]

I worked on a lot of those "hydrovac" Brake systems. as a mechanic for UPS from 1979 to 2005. You need to sort out all the simple stuff first. Adjust all your brakes, if they are out of adjustment that could result in a long pedal travel. Next bleed the brakes. It is not necessary to pump the brakes as this could cause air in the system to foam or make bubbles that will be hard to get out. Fill up the M/cyl and leave the cap off. Start at the hydrovac. Open the bleeder at the Hydro and let it gravity bleed into a glass jar so you can watch for bubbles. Keep the MC full and bleed till bubbles disappear and then bleed some more! Then open bleeder at farthest cyl, and bleed that one in same manner and work your back. There is a basic test for the Hydrovac function, before you start the truck jump in and pump the brake pedal a couple of times, now press and hold the brake pedal and start the engine, if the Hydrovac is working you should feel the brake pedal move closer to the floor once the engine starts. If the brake pedal does not change (or pushes back) you have a Hydrovac problem. Good Luck! .

 

[john connell]

I love the detailed procedure you have replied, sounds like you know your way around. I'm quite certain you're right about getting the brakes adjusted correctly first but in the event the testing you recommend shows the booster is bad, where do you recommend I start to repair it. There are kits available online, would I simply try to rebuild it or perhaps look for a replacement new unit. I do need to get this working. Thanks in advance for your recommendation. Looking forward to your thoughts. John

 

[Longknife]

(quoted from post at 23:26:03 07/24/23) I love the detailed procedure you have replied, sounds like you know your way around. I'm quite certain you're right about getting the brakes adjusted correctly first but in the event the testing you recommend shows the booster is bad, where do you recommend I start to repair it. There are kits available online, would I simply try to rebuild it or perhaps look for a replacement new unit. I do need to get this working. Thanks in advance for your recommendation. Looking forward to your thoughts. John

John : I am not sure exactly which hydrovac you have but they could be very difficult to rebuild. Some require special tools. I think there is a tag on it with the part number. Do search for a rebuilt one or a there are many places that rebuild them ' just search on line...RH