The Stovebolt Site Forums The Parking Lot Big Bolts Hydrovac question

Does the hydrovac increase the volume of fluid being pushed, or is it just a power boost? My dad is wanting to upgrade his brakes on his 63 2ton, and was wondering if a modern 1ton master cylinder would push enough fluid for the wheel cylinders on this truck.

Hy 57plaid, welcome, the Hydrovac multiplies the force your foot exerts, it doesn't increase volume. Master cylinders are sized to supply the volume of fluid required by the wheel cylinders on the vehicle. Whatever you do, do not go smaller in bore than the factory master cylinder, hope that helps.

Thanks. That confirms what I was thinking. I know about sizing the master cylinder to the wheel cylinders, I'm just looking for a master cylinder/booster combo for the firewall maybe.

On the same note, I have been pondering this ever since my dad brought it up. What would happen if a drum/drum dual master cylinder was hooked up in tandem to the existing line? Would it defeat itself? I'm not heading in this direction, but just thinking out loud. Hmmm.

Can't see or understand how you'd do it to even try...
I'd say not possible, and therefore not a good idea.

Grigg

While we're thinkng out loud, if you were to switch to a dual master cylinder do you have to consider the bore and stroke of each wheel cylinder a chamber supplies? Or, do you just take the bore and stroke of the orginal MC and divide it in half. I would think that newer dual chamber systems have a different volume for the front and the rear chamber, and those would need to be close to the volumes of the wheel cylinders. Then again a proportioning valve may take care of that. Any thoughts?

One way to go is to plumb it as a "dual-diagonal" system, with one front and one rear wheel on the same M/C chamber. That way the displaced volume ends up equal for both chambers of the master cylinder. Several newer cars are plumbed that wat to prevent losing major brake function in case of a failure of one front caliper. On the older systems, the rear brakes only have a fraction of the stopping power of the front, so a pressure loss in the front system results in vastly increased stopping distance.
Jerry

I was just wondering if the combined volume from both pistons would push enough fluid to work the brakes on the older truck

Its the pressure that makes you stop, not the volume of fluid.

But you need to push volume to make it work, someone had put an 1 1/8 master in a6500 I've been working on and it wouldn't get pedal up on it after a rear cylinder overhaul I put in the correct 1 1/4 master and with normal bleeding of the system it works nicely.