The Stovebolt Site Forums The Parking Lot Big Bolts Dual-Reservoir Under-Floor Booster?

Hi! Has anyone installed a dual-reservoir,Drum-Drum power-booster under their "Big-Bolt"? My friend,Billy,(with the '59 Viking 60 bus),purchased one,but we're not sure if it will have enough "boost",for his 10,000 Lb.(E.W.),bus. Kind of an after-thought,I know,but he doesn't have a computer,and didn't really get an answer from the dealer. Any thoughts? THANKS!!

I have one on my 59 3600 and it will stop on a frickin' dime!
I expect that with the bigger brake drums and pads on the big bolts it will stop well.

I would be careful using it on something that weighs in at 10,000# or more.

I would think that if the orginal with a hydrovac on a 10'000 truck makes the passenger wish he had a shoulder harness,I would think that the dual set up would also work,not that its needed.

I make them...... https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=708681#Post708681

Dealers are generally the last and least productive places to go-all they know is VIN:

Thanks,Randy! I know that you make the drum/disc conversion kits. I'm looking for info.,mostly on the drum-drum master cylinder/power-booster swap. I may be interested in your system,should I up-grade to maybe a 350 4-bolt main,that I have from a '78 C-50. Crate motor,with less than 10,000,on the "clock". Will probably swap that rear-end as well,since the C-50 would "run" all day long at 70.

Thanks,Don. That's what I was thinking.

I have the same year and make of bus. Where can I get a booster and for how much?

The MC/Booster set-up sold by all of the vendors are made for the light duty trucks and most use a Corvette MC with about a 1-1/8" bore. Our big trucks require a larger bore (1-1/4" or 1-1/2") to move the correct amount of fluid to the wheel cylinders. If you use a MC that's smaller the pedal will travel farther (closser to the floor) to fill the wheel cylinders reducing your margin of safety.

Mike B

I agree with Mike --- it is important to match based on volume movement and you need the correct size master to do that. A smaller master piston will also require more foot pressure due to the difference.

The master bracket that I make will accept a GM master that you can get in a variety of different bore sizes! I tried out a few on mine and ended up with an 1 7/16" I believe. I started with an 1 1/4" and tried an 1 1/2" also. The bolt pattern is the same on all of the GM master that accept a vacuum booster. When you get into the hydra-vac I think is were the bolt pattern changes!

The difference in size between the size of the wheel cylinders and the master cylinder is just like changing gears. A bigger master cylinder will require less foot travel but a harder push from your foot. Like being in high gear.
In retro spec if you change to a smaller master cylinder wheel cylinders remaining the same, more travel but less force is required.
It is fairly simple to figure out what you need to make the swap first figure out the volume of the stock master. Then the difference in volume between combined rear and combined front wheel cylinders.
This difference is the front to rear hydraulic bias you then need a master cylinder the same total volume as the original with the front to rear bias of your wheel cylinders and that is that in a nut shell.

Thanks,Grant! I guess you summed it up nicely. Now,HOW do you figure the volume of the stock master,and the combined volumes of the wheel-cylinders? The same reservoir dimensions,as well as the same stock bore dimensions? How are we going to know,(before installing) that the "new" vacuum-booster performs as well as the stock hydro-vac? Sorry for the "dumb" questions,but I'm still a novice at this stuff.

Not dumb questions at all I miss stated in saying volume the correct variable the surface area or diameter of the working pistons of the cylinders involved. In most duel master cylinders the port to the rear or nearest the input rod end will have the smallest working area. This is do to the first piston in line having rod in the middle of its working surface to push the second. The diameter of this rod is subtracted from the area of the first piston. This port will most likely be for your front brakes as they will most likely have the least surface area in wheel cylinder piston working area.

I took the easier way out and called the guys at abspowerbrake.com I told them the number of wheel cylinders and their diameters per axle. Also diameter and width of drums and shoes. They set me up with the master cylinder a hydro-booster and mount to work with the factory drum brake system. The mount they sent is really cool it mounts the hydro-booster and master to the frame like factory and uses the stock pedal.

Hi,Grant! Did you purchase the M.C./hydro-booster,for your'56? My G.V.W.,for my '55 6500 is 18,000#. Yours has to be close to that. Mind sharing how much you had to pay? Thanks for the GREAT tip! Love both of your "Babies"!!

Yes I got it from ABS Power Brake they are in California.
I don't remember how much but it wasn't cheap. However I was very impressed with the of what I got and the service was great as well. Everything came as a kit mounting bracket as described above, hydro-booster and master cylinder with remote reservoir.
They were very knowledgeable. The stock hydo-vac system could supply 1,500 psi to the wheel cylinders and the new hydro-boost is good for 2,500 psi.

Wow! Impressive! Thanks for the tip!!

Hey wetwilly5757 if you can get in to my photo bucket account with the link below, it doesn't work right. Photo #34 of 69 in the album labeled 56tasckforces album is a picture of the set up as it came.