69 Limo - how to check for air leaks in rear air lift shocks

[1969cadillac]

Hello - I have just replaced the orig factory airlift system with an aftermarket electric tyre pump and dump solenoid

I have new factory air lift shocks.

Works well except it don't hold air for very long - at 50 psi - goes down after an hour approx.

Q. what is the best method to see where it is leaking air ??  I have checked and tighten all the unions - but don't want to overtighten them !

thanks , Murray

[35-709]

Put a few drops of liquid dish-washing detergent in a spray bottle and fill with water.  Spray all of the connections and any other place that might leak and look for bubbles.

[Big Fins]

The way those little nylon tubes snaked their way through the frame, they could be rubbed raw anywhere.

[TJ Hopland]

You said 'new factory'?   If these are clearly old stock then you could easily have a leak internal to the shock itself.   Even if they are listed as current production I have my suspicions that they don't make em anymore and we are getting old stock.  I don't think a new car has used them since the 90's so its likely a pretty limited market. 

[fishnjim]

R U saying it doesn't stay up after running an hour* or once it's off, it slowly bleeds off pressure over an hour? 
I recall they used to simply put a shrader valve on the shock systems to pump up/bleed off the air to raise/lower.   Does yours lower through the dump valve?   That dump selenoid has to be fail closed/spring loaded, if not, soon as the power is off, nothing holding the valve closed, back flows through compressor.   Also the circuit that operates it has to be correct.   May not work off the stock switch.

I'd check each side separately with a gauge, valve, and air hose.   That'll tell U if it's the shocks, which one, or the compressor side. 
The "snoop" (detergent spray) method can sort out any joint leaks.   
Isolate the compressor and test it for pressure hold.   Could be a check valve issue or back flow or how it was designed to operate.    Maybe the wrong one for what you want to do.
* - These after market DC compressors are usually fairly cheaply made and don't last particularly long, 3-4 years.   You might need to add a small air tank and control the pump off a pressure switch continuously rather than the shocks.   Then an air raise/lower switch will work, that's how my air seat was operated.   But if you don't use vehicle much it'll drain the battery or accept the fact that the level will go down when off.   
Personally, I'd ditch the compressor, and just use with the shrader option.   I had those, and they worked well, no issues.   You run it out under the license plate, gas door, or bumper.

[Glen]

The 69 cars have the vacuum compressors.  No electrical parts.