Invisible air leak

disconnect the trailer when looking for an air leak.

 

I agree with Jerry...has to be the regulator before the chambers.

Is you tractor auto shift?

 

Disconnect the trailer hoses....with the engine running, get under it with a spray bottle (water) and douse the air regulator...should see where the problem is. Look for bubbles, just like checking a tire puncture. If the regulator is solid...then water down the air lines from the compressor to the regulator and watch for leaks.

 

First u got to determine where the leak is:tractor and or trailer or both.
Start with the tractor:is it leaking with parking brakes released or applied?
Check the air chambers.remove air lines and plug them.truck still leaking?
Remove the bolt holding the air bags leveler and hold the leveler in a position to cut off air supply to the bags.truck still leaking.?
Compressor governor gone bad.
Air dryer problem.
U have to eliminate possibilties one by one to find the problem.
13 speed manual is controlled with air,it could be an internal transmission air leak and thats why u cant hear it,pinch the line and check ur pressure.

 

The three most common places we have had air leaks on that era Volvos are the pass through on the firewall, the air supply valves on the dash and lastly there is a junction box of sorts inside the frame trail on the drivers side about half way down the truck. Both the pass through and the junction box have the push style fittings, I was able to find the correct orings at the hardware store to replace them and fix the leak.

 

Hook shop air to the supply tank so you don't have to have it running and find the leak.

Explain the entire issue. You say that everything "looks good" with the engine running. So it builds air at a normal rate, when the governor cuts out, the air dryer purges and it holds air without dropping. Is this true? What looks good? It is working correctly when running or not?

When you shut the truck off, both air pressure gauges drop to zero in 5-10 min? What about the actual tanks, did you physically check every tank for air pressure by pulling the the drain cables? Are they all empty, just 1? Just 2?