Automatic Level Control

[TJ Hopland]

The 79-85 E bodies also really need to be at the correct height too, the independent suspension on those gives you a wacky rear bump steer.   

[Glen]

It' about the 67-70 Eldo's rear springs loosing their springing  resiliency which n turn causesthe ALC compressor to fail from overwork. The real heavy lifting should be done by the springs with the pump as an augmentor. I restored my 68 Eldo  with 3 leaf springs set to proper rear ride height without any weight in the back.  Then I rebuilt the ALC compressor which does it's job as needed without trying to carry the springs loading too. 

The ALC compressor does not work any harder with a greater load or weaker springs.  The compressor maintains a constant 280 PSIG no matter what the load is.  If there are leaks in the system that will cause the compressor to work more (but not harder). 
The shocks need to have some pressure in them at all times or else the air bag will collapse and chafe until it leaks.  That is why the factory springs do not hold the full weight of the rear end.  The system is designed for the shocks to hold some of the weight.   With stronger springs and the residual pressure in the shocks the rear end must be high. 

[Rob Troxel]

I get what you are saying Glenn, but with well over 200 PSI trying to hold up a sagging rear end on a car with failed springs, the extra work along with road jounce means the shocks do carry too much of the load and are doomed to fail as well. (Where do you find the special airshocks designed for these cars anymore?)  The ride on my 68 Eldo with three persons  in that back and a trunk load of suitcases is stable and cloud like. With the old single leaf springs, it was boom, bang, clang.

[Glen]

For the 68 ELDO I had to convert to Gabriel shocks. The air fittings are different but easy to convert to. Plus, the air bag is better protected. 
The compressor fills the reservoir to approximately 280 PSIG depending on how strong the vacuum from the engine is.  But the shocks cannot take that much pressure so there is a regulator (the thing with the yellow cap) that drops the pressure to 125 PSIG. 
When the system is working right I have never had a problem with the suspension bottoming out even with a trunk load of tools. 

[Rob Troxel]

Thanks for the tip on the Gabriel shocks Glenn. When I went to rebuild the compressor, the regulator valve parts had exited under a previous owners watch. Found an NOS regulator though some years ago.  Can imagine the parts are now hard to come by.

[Glen]

The regulator also acts as a safety valve and blows it guts out if the pressure in the line to the rear goes too high.  The reason the pressure goes too high is because the regulator valve gets a bit of dirt in it so it won’t close. 
Go here: http://wikicadillac.org/tiki-index.php?page=Automatic+Level+Control to see how to prevent that.   I tie a sock over the regulator to catch the parts if it does blow.  On the Eldo I sometimes find the parts in the body mount just below compressor.