Is this normal for an AMK compressor?

[allegro]

A few times recently I have heard a percussive, repeating jack-hammering type sound when the air suspension compressor is running on my 2012. No codes or suspension performance issues, just a loud sound that shows up periodically. Only pattern is that I notice it mostly when temps are near or below freezing.

Today I dropped the rock slider (which has a beefy compressor protector welded onto it from the previous owner) to investigate and found a lot of road grime and crushed gravel (Northern California winter roads) resting on the protector, below the compressor.

My theory is that the compressor vibration dampening “feet” were hitting the accumulated dirt, and making a particularly loud racket when that dirt-sludge is frozen. Does that seem like a plausible explanation?

Looking at the compressor, the feet protrude well below the mounting plate - is this normal? Picture attached.

Wondering if my aging compressor could be exacerbating the problem... starting to sense a compressor and air strut binge as I near 125k miles since I want this thing to remain on the road for a long time. That said, if refreshing those dampening springs would help, I’m fine riding this compressor out a little while longer. I believe my truck is in the “old-design AMK” / compressor TSB group, fwiw.



Thanks for any thoughts.

 

[ktm525]

Was the AMK original or were 2012s still using the Hitachi?

 

[ryanjl]

What your are seeing with regard to the feet is normal. The compressor is "sprung" in the mount, and the feet hang a little below to allow the compressor a tiny bit of uptravel.

I'm guessing your assessment is correct and the compressor was hitting dirt. You can try to cycle your compressor and even drive around on a clean road without the sliders there to see if it still makes the sound.

 

[ryanjl]

Was the AMK original or were 2012s still using the Hitachi?

I think around 2012 was the crossover, so some may still have the Hitachi.

I've typed this elsewhere, but common Rover lore was the switch was made due to purported better reliability of the AMK unit. I have read something, however, that indicates the switch was made because the Hitachi plant was damaged/wiped out in the Fukushima disaster, which happened in 2011.

 

[allegro]

Thanks @ryanjl - took a test drive today after removing the dirt on the slider and it sounds good so far.

@ktm525 I believe this AMK is the original compressor - I’m the second owner and don’t see a compressor change in the records, and my VIN just barely falls within the “Hitachi or old style AMK” range in the attached TSB. I wonder what the differences are between old vs new AMK besides what looks like a small change to one of the air connections.

 

[DaytonaRS7]

maybe completely unrelated, but i am in the process of buying a volvo (with air suspension) for the wife. reading up common problems, a knocking air compressor when cold (freezing and below) is a common complaint. Problem: moisture in the lines.

Ironically, people on volvo forums question why volvo didn't follow suite of Land Rover and install a dryer with Desiccant in the system.
Maybe something to consider investigating?

hopefully you just have dirt/grime and freezing temps causing things to be a little tight though.

 

[ktm525]

Thanks @ryanjl - took a test drive today after removing the dirt on the slider and it sounds good so far.

@ktm525 I believe this AMK is the original compressor - I’m the second owner and don’t see a compressor change in the records, and my VIN just barely falls within the “Hitachi or old style AMK” range in the attached TSB. I wonder what the differences are between old vs new AMK besides what looks like a small change to one of the air connections.

No idea. My LR3 has had two compressors while the 4 (2010) is on the original. No idea why some work, some are noisy some are not lol.

 

[ryanjl]

Sounds like it may not need to be done right now, but if you are good at all with a wrench (and it seems like you are at least a little if you removed those sliders), replacing the compressor is fairly easy.

If your existing is a Hitachi and you want to go AMK, you'll need to reflash the ECU. A tool like the GAP Diagnostic IID Tool can do that.