Getting the value of %damage?

Let me explain what it is I'm trying to accomplish for clarity:

I am working from the racing mod, so the vehicles in question (hover vehicles to be specific) are the player entity.

I have defined the necessary datablock and script functions to allow damage to be applied to the vehicle as well as energy consumption through turbo/ jetting functionality.

What I'm working toward is a type of sheild system - not unlike that of Tribes2 - where incoming damage is applied first to energy, after which any remaining damage is applied to the health of the craft.

I have defined an onImpact() function to handle collision with terrain/ interior objects, an onDamage() function which seems to be required by the engine, and a damage() function wherein any damage inflicted actually gets applied to the vehicle.

onImpact() -

//---------------------------------------------------------------
function HoverCycle::onImpact(%this, %obj, %collidedObject, %vec, %vecLen)
{
     %obj.damage(0, VectorAdd(%obj.getPosition(),%vec),
     %vecLen * %this.speedDamageScale, "Impact");
}

onDamage() -

//---------------------------------------------------------------
function HoverCycle::onDamage(%this, %obj, %delta)
{
     // This method is invoked by the ShapeBase code whenever the
     // object's damage level changes.
     if (%delta > 0 && %obj.getState() !$= "Destroyed")
     {

          // Increment the flash based on the amount.
          %flash = %obj.getDamageFlash() + ((%delta / %this.maxDamage) * 2);
          if (%flash > 0.75)
               %flash = 0.75;
          %obj.setDamageFlash(%flash);

     }
     //if player is dead, kill him!
     if (%obj.getDamageLevel() > 1.99) {
          %obj.setDamageState(Destroyed);
          onDestroyed();
     }
}

damage()-

//---------------------------------------------------------------
function HoverCycle::damage(%this, %obj, %sourceObject, %position, %damage,
%damageType)
{
     if (%obj.getEnergyLevel() > 0) {
     //Decrement energy before health - emulate sheilds
     %newEnergy = %obj.getEnergyLevel() - 80; //Should be - %damage
     %obj.setEnergyLevel(%newEnergy);
     
     //If we went below 0, fix it
     if (%obj.getEnergyLevel() < 0)
          %obj.setEnergyLevel(0);
     }
     
     if (%obj.getEnergyLevel() == 0)
          %obj.applyDamage(%damage);
     
     // Deal with client callbacks here because we don't have this
     // information in the onDamage or onDisable methods
     %client = %obj.client;
     %sourceClient = %sourceObject ? %sourceObject.client : 0;
     
     if (%obj.getDamageState() $= "Destroyed")
          %client.onDeath(%sourceObject, %sourceClient, %damageType, %location);
}

Now, as you can see above, the damage() function takes in an argument called %damage.

The first thing I'm doing is testing the object to ensure that it has energy - no problems so far.

If it does, then I decrement energy using %obj.setEnergyLevel(%value). Still no problems, except that I'm currently having to calcualte using a constant value.

For some reason, if I change the statement which calculates the remaining energy to - %newEnergy = %obj.getEnergyLevel - %damage; - nothing happens. It's as if %damage has no value assigned?

What makes this more confusing is that when %obj.applyDamage(%damage); gets called, the damage gets applied appropriately?! Obviously %damage has a value, but why can I not access it in a simple calcualtion?

~ Thanks in advance for any help.