Questions and Answers
Bus Brakes
Q. I have a 1958 Ford school (20 passenger) bus. I am trying to get rid of the single brake line master cylinder and upgrade to a two line system have changed it to a 73 chevy master, pedal, and vacuum booster but can't seam to get enough fluid to the rear drums. It has dual wheel cylinders in the rear. The original master had an 1.25 bore and the 73 chevy is also a 1.25 bore. Second idea is to leave out the switch block and run the front line off the master to the right front and left rear. and the rear line off the master to the left front and right rear. I don't know if front and rear of master cylinder put out the same amount and pressure of fluid.
Would appreciate any help or ideas,
WayneA. This is an interesting question. I have never worked on buses and they are quite different from cars. I can try and give you some general advice and you can see how it applies to your situation.
The bores of the two master cylinders may be the same, but is the stroke the same? If you don't have the stroke, you will not be able to push enough fluid to the rear to operate the dual wheel cylinders. Also, look at the rubber brake hoses. If they are old they may be blowing up like a balloon and taking up the pressure that's supposed to go to the wheel cylinders.
The LF/RR and LR/RF idea is a good safety design. If one chamber goes bad, then you will have reduced braking power, but it will still be evenly distributed front to rear and left to right. I would still leave the proportioning valve in, but route the lines in the X pattern.
Good luck with the project and let me know how you make out.