The Stovebolt Site Forums The Parking Lot Big Bolts Dual bore master cylinder

Has anyone put a dual bore master in a 2 ton truck. Buddy of mine has a 48 2 ton. Looking to keep the drum brakes but upgrade to a dual bore master. Suggestions? Pictures?

Thanks

Friend installed a drum/drum dual reservour M.C.,in a '59 Viking bus recently. he couldn't get brake pressure to the rear,even with "solid pedal". He took it to a nearby shop,that does brake work regularly. They removed the rear drums,and nothing was broken,and even had like-new shoes! mechanic applied 100# of pressure to the rear cylinders,and got minimal results! None of the lines are clogged! he purchased his under-floor M.C. from one of the reputable parts suppliers,but it's designed for pick-ups,not the 1-1/2-2-tons. The bore is smaller. I suggested a proportioning valve,but that wouldn't help,if 100# pressure barely moves the rear wheel cylinders! Bus is parked,until brake problem is remedied. This is the reason the bus got parked in the first place-same problem with a stock M.C. Really puzzling!

Rubber brake flex lines can close up inside, or have a flap of rubber loose that acts as a check valve, weird things can happen.

I agree with Grigg on the hose being collapsed inside. Easy way to prove it is to break the connection at the steel to rubber junction over the rear end and see if you have pressure to that point.Pressure at the steel line before it goes into the hose means the hose is bad that feeds the rear brakes.

I make a bracket to install a 1 ton dual circuit master in place of the original. You can use a number of GM master's with different bores. This replaces the hydra-vac as well. I have about 4000 miles on my set up and it does excellent.

You can find the thread here https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=964265&page=1

Yes I have a hydro booster and dual circuit Master cylinder in my 56 6100 I believe it is much safer than the stock single circuit master.
I didn't build any of the system it was all put together by ABS Power Brake. I am sure that the mounting bracket is much like what Randy Domeck above offers. The bracket ABS provided mounts the master cylinder under the floor using the same holes in the frame that mounted the original and uses the factory pedal assembly. The hydro booster and master cylinder were sized appropriately from another more modern medium duty truck with the same sized brakes.

Wetwilly as far as your friends bus the first thing I would do is check the rubber hose as Grigg suggested above. If the hose is clear then I would check to see that the ports on the master cylinder are connected front to rear correctly. The port at the push rod end of the master cylinder has a smaller working area and should go to the front brakes as the total working area of those wheel cylinders is smaller than the rear. If they are connected the wrong way the front brakes may be getting full pressure and making the pedal hard before there is enough volume of fluid sent to the rear to actuate those brakes.

Hope this all helps both of you.

Heavy who did you speak with at abs?

It's reasonably important to have the right size bore MC for the brakes you're trying to use it for. A big truck has large bore wheel cylinders and needs a larger bore MC (than one from a small truck) to move the required fluid to operate them.
Good starting point is to replace the MC with the same bore size as the old one.

Yes rear cylinders are 1 1/2" front 1 1/4". I'd like to get a dual bore master with a hydro boost under the floor with stock pedals

You also must keep in mind that with the big trucks the rear often has two cylinders per wheel.

Fat boy I am not sure who it was they were how ever very knowledgeable and friendly but it wasn't cheap about $700.00 for the bracket and master cylinder.
If I was going to do it again I would source The bracket elsewhere and look for trucks with nearly the same brakes at the wheels and have the master and booster you want and hit the big truck wrecking yards.

Only one

Thanks hevy

If it weren't for people like you,there would be a whole lot of parked '"Bolts",out there,rusting away,and not running! I tried telling those guys ,at the shop, (where the bus was taken),about the old hoses,and the in-correct bore. They just gave me a "dumb" look,and kept troubleshooting the same stuff,over and over again! a lot of you gentlemen are engineers,with decades of experience! I THANK-YOU All,for helping the novices,such as myself! It pains me,though,when you quote common-sense solutions to "mechanics",that don't listen! Maybe because he's getting paid by the hour,and doesn't want to find the cure too quickly?? THANKS,GRIGG,and HEAVYHAULER!! I'll pass along the info,and hope it doesn't fall on deaf ears! I'll let you know how it goes...

I'm working on this same plan for my '54 350. It has a 1-1/4 inch M/C original,and I found a M/C from a Chev/GMC one ton van is also 1-1/4 inch bore,but dual circuit,and the lines,when installed under floor,will be in the side facing the transmission. I'll have to get a universal proportioning valve and buy some brake lines. I'm going to try building my bracket first,but if it turns into too big of a cluster-kluge I'll have to but one. My Master Cylinder was hooked to a Hydro Boost,but it'd be a pain rigging a pump etc,so I'm running it w/o a booster for a while. Since the lines have to go back to a crossmember then forward again to where I split the front and rear brakes apart,if I get a booster that fits my app. all I'll have to do is move the M/C back enough to mount the booster and put a couple of "S" curves in the lines and I'm set.
Speed

Keep in mind that most non power brake systems will use a smaller master cylinder than their powered counter parts. The master cylinder will require a longer pedel travel to move the wheel cylinders the same as the larger one would. Like using a lever to move something the longer travel of the pedel the same as using a longer lever without power assist you may need this mechanical advantage to provide adiquit stopping power.

What year and model chevy 1ton van?
What is the bore size?
Was master meant to be with a booster originally?