For some time the IronMan had been making some "clunking" noises not of the normal Isuzu driveline flavor. At first I suspect maybe the CV joints were failing and after inspecting found them just fine. Visually inspecting the chassis and driveling above and below revealed nothing obvious, so I continued to drive and listen. The noise began to worsen and I noticed the shift levers moving significantly during accelerating gear-shifts. This is typically a sign of failed or failing engine mounts. I also noticed the noise, and even felt it to some degree, during turns with lateral acceleration which further strengthened the engine mount diagnosis. So, confident I had determined the problem an order was place to Autozone.com for a pair of new engine mounts.

This past weekend I set aside some time to exchange the IronMan's engine mounts. While preparing for the swap I was getting a closer visual inspection of the mounts from below and noticed they looked fine. Perplexed, I began going down the driveline with more scrutiny. As I grabbed the transfer case to pull myself toward the rear it shifted. Taking a closer look at the transmission mount, the 3rd member of the drivetrain mounting trio, I dicovered the left-side bolt and heatshield missing along with the right-side bolt. So I dropped the skidplate to find the left-side bolt and heatshield laying on the top of the plate. Somehow it managed to rest there after it's fall! Inspection of the bolt revealed thread damage near the bolt head lessening toward the end, showing how it supported the torsional load from the tranny until finally dropping out. There was no sign at all of the right-side bolt.

A quick trip to the local Grainger secured two replacement bolts which were installed and torqued to spec. Problem solved! Thankfully I can return the unused engine mounts to Autozone, so total out-of-pocket for this repair was less than $5. So when you hear some clunking going on, just slide under the side and give the transfer case a good pull and shove. If it moves, then you've got an issue with the transmission mount (AKA rear engine, or motor, mount).

Here are a few pics taken during the repair where you can see the deflection of the transmission relative to the mount on the crossmember: