Vibration damper

Is it a rubber mounted damper? It’s Normal for rubber mounted dampers to have wobble movement. Cummins allows almost 1/4 inch tolerance of radial runout before replacement. Its the rotational movement you need to worry about on those. Has it clocked away from its original setting? Thats when you worry about those because they are actually moving. After you get the new one on and fire it up you will have immediate disappointment when you see it wobble too.
If it is a viscous type than you should have very little wobble movement because they are either machined out of one billet piece or “precision” welded together.

 

You should be ok. As long as they stay oil free and no chemicals or flame get to them those rubber mount ones rarely need replacement. Some of them look horrible if they have a lot of wobble but that usually doesnt hurt anything.
My old Cummins shop manuals only recomend replacement.
1) if it clocks away from setting because that screws with the timing. Some of the older ones had timing marks on damper instead of the accesssory drive pulley.
2) has more than 1/4 radial runout wobble (can cause clearance issues)
3) or if it starts throwing belts.

I have an ‘72 NH 250 with a rubber wobbler. Thats been 48 years. No damage.
I also have a’99 baby Cat 3126 with over million miles on rubber damper ( same damper on 3rd overhaul) that has wobbled since birth.

The viscous ones do need to be replaced at the times that the other guys have already stated no doubt. They are a different deal.
That being said I have seen some 50 year old ones still being used. I just replaced the original viscous one on a ‘74 NTC 350 small cam that has never quit running since new with 2 overhauls and probly 2 million on it. Still couldnt tell if it was bad or not. Shoulder shrug!