How do you know if a harmonic balancer is bad?

[CN Spots]

Is there a way to test them at home or will I need to take it to a shop? (My dad suspected it was bad due to an odd vibration in the truck at speed).

Oh, and why are those things so #*@&%$ expensive???!

(1968 Ford 390FE)

Thanks,
spots

 

[G1K]

Re: How do you know if a harmonic balancer is bad?

Make a mark across it with a paint pen. Drive around for a bit. Check to make sure the line is still a line. If the balancer has spun, then the line will be broken. If it's broken, time for a new balancer.

R

 

[Reel Poor]

Re: How do you know if a harmonic balancer is bad?

If it's an engine vibration it should also vibrate in neutral at the same rpm's he is noticing the vibration at speed. If he only feels it at speed on the road it's probably a u-joint or tire problem.