The Stovebolt Site Forums The Parking Lot Big Bolts 'new' brake system - no hydraulic pressure

Hello - Still working on my '58 Spartan 80. I thought I did everything the right way, but '0' brake pedal. The original master cylinder was rebored, sleeved and rebuilt w/ all new parts. Instead of the original AOHC system, I replaced the power boosting system with a c. 1970 remote Bendix unit which has been professionally rebuilt. Wheel cylinders (2 @ ea. wheel) all new, and I hooked up just one rear corner, plugging the 'T' connections, to test the system. Bled the system 4-5 times consecutively, ending with no air bubbles whatsoever, and still nothing....pedal all the way to the floor, easily by hand, even with all bleeders tightly closed and no external leaks whatsoever - and will not build pressure, even when trying to 'pump' it up. I'm thinking 'hidden' air pocket; improper rebuild of either master cyl. or booster, causing internal hydraulic 'blowby'; or possibly hydraulic 'engineering' problem(?)by using 3rd generation vacuum booster with old type master cylinder. I know the later boosters have smaller diam. but longer power cylinders than the hydrovac type, but both supported same size dual wheel cylinder systems, so I can't see why that would make a difference. If anyone has been at this point and figured out the problem, I would sure appreciate your guidance. Thanks!

Jay,

Did you bench bleed the MC before you installed it?

The Cups in the MC could be installed backwards.

Are your brake shoes adjusted so there is a little drag when the wheel is turned by hand? Kind of sounds like the are, as pumping normally will make the shoes make contact if they are out of adjustment, but I just had to ask anyway.

Mike B

Mike - right away, you identified something I didn't do: bleed the MC. I'm not sure even how to do it, but now that you put it in print, I suddenly remember reading it in all kinds of repair manuals...WHOOPS! I can research the proper procedure, or will listen to your description, if you have time to post it. Also if, after that, the problem still exists, I will definitely check the MC internals - wouldn't be the first time that assembly was done wrong...thanks for the feedback on this.........

jay, to bench bleed I like to make me two small lines...usually by cutting off two old ends, and then screw them in the m/c and bend the lines back over into the m/c. Besure the ends are down in the fluid good. Then as you "pump" the m/c do it nice and easy and until there is no more bubbles coming from the end of the lines. Then disconnect and put a couple plugs in the m/c unless you can attach your truck lines pretty quick.

Can you hear anything happening inside the drums? Is there any movement of the shoes?
Scott

And don't forget the rod to piston adjustment at the master, the push rod from the brake pedal into the piston needs to have a little movement before the piston starts to move, if its holding the piston in an applied position it won't let fluid in the chamber,and you don't get enough travel.

Great feedback - I'll use the bleeding method suggested and I'll check the rod to piston freeplay. Scott, I left the drum off on purpose - there is NO wheel cylinder or shoe movement.

Sounds like an internal master cylinder problem,
Scott

i had the same problem. it was air in the lines when i was certain that they were clear of air. hang in there you'll figure it out. -DVZ

I would advise against placing the lines back into the MC as you bench bleed. If you do have air in the MC you will just be returning it to the brake fluid in the master cylinder and arieated brake fluid is hard to get settled down so it can be reused. Best to capture it in a clean jar and use new fluid to keep the cylinder level full. Brake fluid is expensive so be carful not to let it get dirty.

Placing the lines back into the MC is the standard method I've always seen in manuals and intructions included with replacement MC's, And, I do agree that aerated brake fluid can be a factor in the process. While bleeding into a separate container, make sure the hose end remain below the bled fluid level to prevent any air being sucked back into the MC. You may need to put a small amount of fluid in the container at the start of the process.