Air dryer going bad?? 911

[Devin & Amy]

Hi all,
I'm in the U.P. and today we developed a growl in the area under the old ramp. I'm pretty sure it's the air dryer. I have a 1980 MC9.
Is mine the AD-2 or AD-4? how do I tell.
is this something that's going to get worse, fast or gradual?
Is it an emergency fix?

If I keep the rev's up it goes away (i.e. fast idle or just normal driving), but when I come to a stop it really growls.
Easy fix, or full rebuild?

Devin

[Hartley]

It may be as simple as removing the dump valve at the very bottom and cleaning it.

The growl could also be just one of the auxillary air tank feed valves located near the dryer.

Or a leaky front leveling valve. They can grumble, growl and hiss at the oddest times if they need replacing.

All of this means that you have to get under the bus so jacks, blocks and ramps may be required.

Never trust the air suspension... NEVER ! You might get trapped, flattened or maimed if you live !

[gumpy]

This actually sounds like air entering the front air tank, which could mean you have developed a leak somewhere which needs replenishing. Possibly a suspension leak.

Suggest you run up on some 4x4s or 6x6s and get underneath to pinpoint exactly where the growl is coming from.

I doubt it's the air dryer.

[TomC]

Typically when an air dryer goes bad it starts to cycle often-like once a minute.  You hear the spitting of air coming out often instead of it only happening when the dryer cuts off the compressor.  Or if the compressor does not want to build pressure and you hear air escaping from the bottom of the dryer.  A leak in the system sounds more logical, since the check valves can make a "growling" sound.  Good luck, TomC