Any ideas how to pressurize the air system of an '01 Mack using an outside source of air? Do I remove the air tank bleed valve and pump air in through there?

Also, just today, I learned that trucks of old had starters turned by air pressure. Why is that system pretty much done away with today? It seems like a good way to save battery power, especially in the winter.

 

Yeah, get the proper size fitting to screw into where the bleed valve goes, and hook your hose onto it.

They were also a great way to not have your truck start, especially in the winter. The air systems on trucks are notorious for having moisture in them, and in the winter, that moisture becomes ice. Can't start a truck if the line is frozen. And also, can't start the truck if you develop an air leak that drains the system.

 

Much better to remove the line from the air compressor and put your air in from there. Once full, just disconnect the air supply and your system won't empty itself as there's a check valve in that line.

 

Find the "pop off" (relief) valve on the air dryer.

Remove said valve, put a "T" fitting in where the pop off valve was, put the pop off valve in one port of the "T", and put a 1/4 NPT X 1/4" air line fitting into the other port of the "T". Connect a length of 1/4" plastic air line to the fitting, run the air line to a convenient location on the outside of the truck and use a 1/4" air line X 1/8 NPT female fitting and screw a Schrader valve (it looks like a tire valve) into the 1/8 NPT fitting.

Make a suitable bracket to secure the Schrader valve, and use zip ties to secure the plastic air line out of harms way.

This way you don't have to get dirty climbing under the truck to air it up, and it's connected at the air dryer, so all tanks in the system will get air.

 

Here is what the "pop off" valve (relief valve) looks like:

 

Here's a photo of a truck I put together where I work, showing the external air fill, just below the top step.

In our case we put a "male" shop air hose connector and a shutoff valve on it, that way we hook an air hose on, open the valve and pressurize the system. Once pressurized, shut off the valve and disconnect the shop air hose.

You can substitute the aforementioned Schrader valve for the shop air connector and shutoff valve.



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O.K, I hate to be the "dumb" one but I got to know......why would you want or need to supply air from an external source?

 

That's where you hook up an air hose to the tank. For airing up tires, etc...

 

One reason would be if a truck has dead batteries and is also out of air, you can pressurize the air system to release the spring brakes and then pull start it.

The reason we have them on all our trucks is so that when we have a truck in the shop and we're working on the brakes or some other part of the air system, we can keep the system charged, or re charge the system without running the engine and smoking up the shop.

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Actually, if you want to use truck air for filling tires, you should put a connection on one of the "dry" tanks.

Air from a connection piped into the air dryer as I described could be contaminated with oil & moisture, both of which are bad for tires.

So:

To fill system, hook into air dryer.

To draw off air for other uses such as tires etc., hook into one of the "dry" tanks.

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