How do you know if the harmonic balancer needs to be replaced?

Thanks for any comments.

In center of it is a rubber like elastomer, (may need an inspection mirror) if it's swelled or cracked time to go, some recommend to be safe change at 100K miles as a preventative measure, if it's already gone there will be a hard metal to metal clunk when you start (don't drive it this way if you find this to be the case; high probability of broken crankshaft soon to follow

I have not noticed any clunking noise at start-up, but installed a remote FSD last week end and now seem to feel a vibration while driving the truck at highway speeds.

I will do visual inspection.

Vibes are a tuff nut to track down if balancer is okay, open a new thread for vibes problem I don't think we have a FAQ for that, we could use your problem as a discusssion for this and entry into FAQ.

Smokey,
this link as some pics of what my broke harmonic balancer looked like.
http://dieselplace.com/forum/showthread.php?t=49608&highlight=harmonic+balancer

Ditto, change it at 100k ( maybe 125k )

Waiting untill something breaks is not cost effective....

Look at it this way:

I do not think you would want to fly on airlines that waited
for a critical part to fail before replacement....vs replacement by time in service..

I did mine at 120k, mechanic said, it's still good, i said, change it, when he pulled it off and inspected it up close,
his comment was , learn something every day,,,,