2004 XJ8 ~85,000 miles. A few days ago at the end of a long drive there was a clunking noise in the front end when I went over bumps. At fist it seemed like just the front right, but maybe left, too. The next day the noise was much louder and clearly on both sides; third day, too. On the fourth day, after a long drive with the clunking on every bump (but quiet at hwy. speed on a newly asphalted road) I stopped and sat in the car a few minutes and there was a sort of humming noise for 2-3 minutes in the front end which suddenly stopped. After an hour I got back in the car and the clunking noise was gone. What I'm wondering is whether this sounds like the air shocks didn't engage for a few days and then went back on. I can't imagine a more mechanical thing like bushings going out being loud and then suddenly quiet. So, that's the first question - Could this be a faulty air suspension problem? Second question - Is there a way to diagnose a bad switch or something that failed to activate the air suspension? Last question - If the problem returns and is a major replacement, I've heard that air suspension systems are mighty expensive so I'd probably opt to have them removed and just use standard shocks instead. If I were to do that, any recommendations on really good shocks to replace the air suspension system in front?

 

wmlaven;
Given the age of you vehicle and the mileage it is not unreasonable the air-springs could be going bad. Typically the air bladder in the air spring goes bad (leaking air) before the actual damper portion (shock) goes bad. The humming noise for 2 min could be the air compressor. The compressor is protected from over temp by limiting the on-time to I believe 2 min.
Are you noticing any change/sag in the gap between the top of your tires and the fender edge above it? This could indicate an airleak.

I've replaced airsprings on my 04 XJR to correct leaking air but I found the mechanical clunks over bumps we the result of worn upper wishbone bushes. You may want to have your suspension bushes closely inspected before assuming the airsprings are the problem.

- William

 

Thanks, WWR. At first I thought the clunking might be bushings, but then the noise stopped after I heard that humming noise so I thought that maybe the air compressor failed for a few drives then worked again. If the bushings were worn, I would assume that noise wouldn't go away, but would actually get worse with more driving. I'll keep an eye on the tire to fender edge gap.

 

I have read of many air strut failures on this forum and the symptoms are usually:

A loud bang and one strut immediately collapses right down.

A strut (or struts) sag due to air leaking.

The hydraulic section of the strut rattles and the source cannot

be traced until the strut is replaced.

You need to find the source of the rattling but don't worry about the air

suspension just yet.

The ARB (sway bar) is a possibility.

 

I'l keep listening, but what's still a mystery is that it was noisy for a few days, then the humming at the front end for a couple minutes, and then no noise since then.

I would think that a sway bar problem, just like a bushing problem, would be noisy and stay noisy once it got worn to that point. The disappearance of the noise is what confounds me.