The Stovebolt Site Forums The Parking Lot Big Bolts Air Brake upgrade

Hi I would like to upgrade the rear air cans on my 1951 GMC 620. I thought of putting spring cans on. Has anyone done this and where is a good source for parts?..............Richard

I would like to do this on my '59 as well, with the least amount of modifications so as to not permanently alter the vehicle..

There is something unsettling about the thought of losing the brakes on something that heavy. I just hauled a car on mine & this crossed my mind every time I touched the brakes.

Not familar with that early air brakes. Are the bolts in the same place if so I don't see an issue . some of the first trailers I pulled did not have spring brakes seems like the mounting bolts were the same though. next question do they have a reserve as well as normal service air system? Are they S cam brakes or wedge brakes? If the mounting holes are the same any truck parts dealer would have the boosters/chambers/cans look at this been around trucks all my life and don't know the proper term. I've heard them refered to as chambers and as boosters but this is the first for cans but that may be correct.

hmmmmmmmmmm. kb-3. sounds like antique corn picker to me. yeah you guys can do this, and here's how (get ready to put this in the tech section mom)

here goes.

first let's look at what you have. the one and only air tank is a SERVICE air tank. on some road tractors of that era there might have been an additional air tank called an emergency tank, but really all it was for was for parking. the parking brake was applied with a push pull control valve that applied pressure to the brakes. when the pressure went, so did the brakes. (you diesel guys never leave the truck in gear when ya park it, right?)

to bring yer big rig into this century is pretty easy, and requires a few simple modifications.

1. yep, the BRAKE CHAMBERS should be the same size as the original. remove the upper part of the chamber by unbolting the top of the brake chamber that's currently on the truck after disconnecting the air line. it should pop off due to the spring inside. there's a rubber piece inside called a PANCAKE. when you go to the big truck parts joint buy a new pancake, and see if you can get a new return spring. (ever see them 1/2 mile long skidmarks on the road? bad return spring usually, and if gives tire dealers a warm and fuzzy feeling in the wallet).

o.k. next.

you have a new pancake and return spring. these are for the SERVICE brakes. you install a new COMPOUND BRAKE CHAMBER on top of where the old brake chamber was, and hook up the SERVICE air line to where it oughta go. it should be marked.

now you need to run new EMERGENCY brake lines to another PUSH PULL CONTROL VALVE in the cab

run a new air supply line to the new air tank you scrounged at the junkyard. this is the emergency air supply tank.

run a new air line from the control valve to a supply port. this can be on the original air tank, or anyplace that gives a constant supply of air. there needs to be a check valve in this line someplace to prevent the backflow of air from the emergency air tank back into the system.

sound complicated don't it? it ain't really.

here's some misc. stuff.

run plastic air line, and if ya can, replace the air line you have with plastic. it lasts longer, is much cheaper, stands up to weather, and oil much better, is easier to install and you don't have to have them custom made up.

other than that, it just as good as the rubber crap.

red is the color of emergency line, green is service.

run any air line like an oil line. that means don't let it chafe other lines or metal objects like bolts and the frame. use plenty of clamps and wire ties. if you decide to not do this remember that loud hissing sound comes just before yer nose smacks the windshield. oh yeah, there's the tire guy getting that feeling again, as you skid to a stop.

O.K. NOW YOU HAVE REAL EMERGENCY AND PARKING BKAKES. THIS NEXT PART CONCERNS YOUR SAFETY, AND HOW LONG YOU INTEND TO LIVE OR AT LEAST HOW MANY FINGERS AND EYES YOU ARE BURIED WITH.

UNDER NO CIRCUMSTANCES ARE YOU TO EVER TO UNCLAMP THE TOP PART OF A COMPOUND BRAKE CHAMBER. THERE IS A MASSIVE SPRING COMPRESSED INSIDE THAT CAN AND WILL UNSPRING WITHOUT WARNING IF YOU LOOSEN THE EMERGENCY BRAKE CLAMP!!!!!!!!!!!!!.

if the top of a brake chamber ever leaks air, you replace the entire chamber. you can change a service pancake, but NEVER an emergency pancake. the way the emergency chamber works is air pressure overcomes spring pressure to release to brake. as air pressure decreases, the spring takes over and applies the brake.

you may find a diagram on websites from

anchorlock

berg

american brakeblock.

next time ask an easier question will ya? my 2 typing fingers are sore.

try this.
Copyright (c) 2005: Queen's Printer,
Victoria, British Columbia, Canada This is not the official version.
Important Information (disclaimer and copyright information)

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MOTOR VEHICLE ACT REGULATIONS — Continued
B.C. Reg. 26/58

Schedule 6
Approved Air Brake Systems
[en. B.C. Reg. 5/83, s. 3; am. B.C. Reg. 84/85.]

"L.75" Air Brake Diagram:




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Copyright (c) 2005: Queen's Printer, Victoria, British Columbia, Canada

I haven't converted any thing that early to spring brakes but I have converted some older trailers to spring brakes and it was relatively easy to do. I would definitely take Koolcar's advice, especially regarding disassembling the brake cans. Going by what systems I've worked on, one thing you will have to change, other than the cans, is the valve which is usually mounted on the cross member by the axle. The single diaphragm valves that I've seen had a service line from the foot valve going in, an emergency line from the emerg./park brake valve going in and a supply line going in or sometimes its mounted right on an air tank outlet. Going out you have a service line to each diaphragm. On the dual diaphragm valves you have the same lines going in but you have an emergency line going out to each can as well as a service line. The service side of both systems operates pretty much the same, but on the single diaphragm system when you apply the emerg./park brake and evacuate the air on the emerg. line into the valve, it it applies line or tank pressure directly to the service line to the diaphragm. It works pretty good until your tank pressure leaks off, then your truck can roll away. On the dual diaphragm / spring / maxi-can system when you apply the emerg./park brake and evacuate the air on the emerg. line into the valve, The valve "dumps" the air on the emergency side of the can and releases the spring to apply the brakes. Your brake will remain applied regardless of the tank pressure in the system.

You can buy the whole maxibrake assembly including service brake portion ready to go then you don't have to change the service pancake. you will have to cut the push rod to proper length to match up with clerances for the slack adjusters, don't know the price differential. If you decide not to upgrade to spring brakes at this time would still recommend replacing the pancakes if it hasn't been done in recent memory. They can and will fail. If one fails you would still have some brakes but you lose airpressure fast and could cause brakes to lock at an inopportune time amd your aircompressor would have to work a lot harder. As koolkar said don't under any circumstances take apart the top chamber of a maxibrake system.

Thanks for all the good info guys. Some thoughts, I have the Trolly Lever in the cab under the right side of the steering wheel and it is currently set up to hold the truck's brakes on,I.E. Press and hold brakes then pull down on the lever, release the brake petal and to release press and hold brakes on then swing lever up. I would like to replumb this to vent the spring cans. This would keep the truck looking original while making a safety upgrade to the brake system. I show letter "B" brake chambers should be installed on the rears with a rated spring force of 44 +/- 5 lbs and a max working stroke of 1 3/4". The truck has two air tanks but both for service.I was told there is two maxi cans available 2430 and 3030 I will do some looking at the sites listed above to learn more and see which one might work.........Richard

interesting on the modern trucks the trolley valve is to operate trailer service brakes only never to be used for parking so I would have had difficulty figuring your set up out

it does the same thing on a straight truck, only it applies the brakes on the truck. it is used so those of us who don't have 3 legs don't have to figure out how to do one foot on the brake, one foot on the clutch, and one foot on the gas when trying to take off while on a hill. it is not---ever-for parking, even for a little bit. air pressure can, sometimes, push the lever back into the release position.

pictures of andy divine from the old wild bill hickock show yelling "wait for me wild bill" come to mind. so do pictures of dead people and wrecked trucks..................

by the way, joe has a pretty good handle on things.

OK I will leave the trolly setup as is and add a proper modern push/pull (yellow I think) parking brake controll for the upgrade. Today I worked on the compressor and mocked up the exhaust and finally I pulled the rear half of the exhaust manifold to replace the studs. Now that I have your feedback for the brakes I will start to get some parts together. I sure do want to thank everyone for thier input..........Richard

Richard,the 2430-3030 designation is just the size of the maxibrake cans,meaning the dia/surface area of the pancake. I,m betting the 2430 is what you need on your truck.your sys. is what they called PRE 101 brake systems that ended at about 1971/72. the 3030 cansthat iv,e seen where usually on something as big as a 82 Mack R600 tandem 12yd dump P.S. they also make 3636 cans. Regards Steve sr.