Diamond T Air Brakes

[Speed]

Hi all;

I'm just wondering about the air brakes on this '47 Diamond T truck I located. Is it legal to operate on the original air brakes,or does it need to be upgraded to modern brake cans and plumbing? I'd guess there's a little different rules for privately owned trucks vs. commercially operated trucks. What all is involved in upgrading to the newer air brake design? Personally,I'd prefer that the brakes set up,and lock the truck down if I break a line over having NO brakes. So,if it's not a huge job to upgrade,I'm planning to reccommend to possible buyers to plan on the upgrade. I was told last summer it's "no big deal-just install new brake cans and jigger the plumbing a little." I don't understand what he meant by that. Of course he does tend to over-simplify things. anyway,any info you might have would be appreciated.

Speed

[chris88]

If you want to put maxis on all you need to do is plumb in an airline going to a park brake knob then back to the spring side of your chambers. I plan on doing that on at least one axle on my mack before she sees the road.

[Speed]

Thanks Chris;

I'm trying to understand what's changed in air brakes. As I understand it,back in the day,air pressure was applied to push the brake shoes out against the drums,and that meant that an air line break caused no brakes. I'm guessing the old style brake cans must have had a light spring inside,since all it'd have to do is pull the brake linkage back and retract the brake shoes when the air pressure was released. Is this how the old style brake cans operated?

With the next generation brakes,the brake shoes were pushed against the drums by spring pressure,and air pressure was used to release the brakes,right? So,if an air line breaks,the brakes actually set up.

Okay-so if we change to the new style brake can,which would have the (much stiffer) spring on the opposite side of the diaphragm as the old style,and reverse the side of the diaphragm the air goes to,the air serves to release the brakes,so actually releasing air pressure applies the brakes. With this in mind,the valve at the brake pedal would have to be connected opposite of the old style set up,or the driver would have to drive with the brake pedal pushed down.

So,if I'm seeing this right,the new style brake cans have to be connected backwards from the old style ones,as does the brake pedal valve. I'm sure there's more to it than this,guess I should read up on air brake systems,as I have very little experience or knowlege in this subject. If I'm off the mark please set me straight.

Thanks for your information and help.

Speed

[Freightrain]

If I recall Bendix has nice diagrams showing common air line set ups. It should point you in the right direction.

I always wonder exactly how Maxi's work. Yes, it takes air to release the park brakes, but when you push on the pedal it applies air to service brakes.....but does it basically push against the air holding the park brake off? I know there are a few air valves(quick release and such) that enter into the system but have never really undertood it clearly.

[MACKS]

It's really very simple, the maxi can has to seprate chambers one is for parking and one is for service, the parking brake chamber has a very strong spring behind the diaframe, when you aplpy the parking brake it exhausts the air from that chamber and the spring then applies the brake, the service brake side only works when you step on the brake peddle.

[Speed]

Okay-so the actual service brakes still work as they always have? With air pressure to control them? So the maxi system is the "lock 'em up if the air pressure drops" safety brakes? Sounds like the brakes still work the same except to run a maxi,you need to run secondary lines and a special valve to it. Interesting set up.

Thanks for explaining it.

(Kinda makes me appreciate my hydraulic brakes a little more,though...)

Speed

[Packer]

Think of the Maxi as two systems.

One side of the maxi has a spring in it. With no air, the spring pulls the slack adjuster rod, rotates the 'S' cam and holds the brakes on. Air pressure is built up when the engine is started, The valve in the cab is pushed, air enters the spring chamber, compresses the spring and releases the brakes.If a brake line to the service brakes wears thru or whatever, the spring is still compressed and stays that way until the air drops below about 60psi.

At this time the spring starts to unwind setting the brakes.

Service brakes work as they are needed; a little air, a little brake - - - A lot of air, a lot of brake. This is where the "Quick Dump" valves that Freightrain metioned comes into the system.

As one more little item pops into my head........... The "Tractor Proction" valve will, in the old systems, will still leave one end or the other with brakes to get to the side of the road - - - or home if ya got big ones!

Packer

Hey Speed!!!

Air won't leave spots in the driveway!!!!! LMAF

[Speed]

Good point,Packer! Plus,air's a lot cheaper than brake fluid...LOL

Hey-I might give you a call later;you gonna be at the 307 number?

Speed

[Rob]

Good point,Packer! Plus,air's a lot cheaper than brake fluid...LOL

Hey-I might give you a call later;you gonna be at the 307 number?

Speed

A hydraulic brake system that leave spots in the driveway is trouble and unsafe for operation; all kidding aside.

Rob

[HeyCharger]

If I recall Bendix has nice diagrams showing common air line set ups. It should point you in the right direction.

I've found this helpful;

http://www.gnb.ca/0276/vehicle/pdf/ab_manual-e.pdf

Regards, Rod.

[ThaddeusW]

If I recall Bendix has nice diagrams showing common air line set ups. It should point you in the right direction.

I always wonder exactly how Maxi's work. Yes, it takes air to release the park brakes, but when you push on the pedal it applies air to service brakes.....but does it basically push against the air holding the park brake off? I know there are a few air valves(quick release and such) that enter into the system but have never really understood it clearly.

As packer said, two different chambers. another things to add is the anti compound valve between the spring brakes and the service brakes. It prevents the spring brakes and the service brakes from coming on at the same time which could damage the brake chamber.

"With the next generation brakes,the brake shoes were pushed against the drums by spring pressure,and air pressure was used to release the brakes,right? So,if an air line breaks,the brakes actually set up."

Speed:

This common misconception comes from people who get the operation of maxi/spring brakes and the service brakes mixed up.

And a little side note on the Tractor Protection valve (TPV). Its real simple, two line run through it, one service (blue) line and the other the emergency/supply (red) line. Its nothing more then a piston controlled valve with a low crack pressure. When the trailer knob is pushed in it pressurizes the red line going through the TPV opening the piston valve which lets air flow through the service (blue) line. If the red line breaks off or there is a severe leak, pressure cannot build to hold the piston valve open closing the service (blue) line which lets the pressure in the tractor brake circuits build. No trailer brakes but you have tractor brakes.

[POWERBRAKEBOB]

THE CONVERSION TO MAXI BRAKES ALSO REQUIRES A "THIRD" OR PROTECTED TANK JUST TO OPERATE THE SPRING BRAKES, IN CASE OF AN AIR LOSS. WE COULD HELP YOU WITH THE PLUMBING OF THE SYSTEM