Like the title says, how does one determine if a torsion bar needs to be changed? Other than visually apparent wear from metal to metal contact, that is. Do they wear evenly? Is it a good practice to replace both rather than just one? TIA, Kent

I would think they should be replaced in pairs

Just like a rear spring with sag…. Not one at a time

I’ve replaced only when scarred from rubbing metal on metal

My personal opinion is replace when heavily corroded, worn from rubbing or broken.
I’m no engineer but I think they differ from springs because springs eventually sag so much, they bottom out. I don’t think torsion bars will bottom out the same way. The sag can be adjusted. At least some what.

Thx Mark and Brandt, that answered another question which was about adjusting ride height on one side only. So is it safe to assume that the intended design was meant to last the life of the car if clean, not worn and the car wasn't tracked??

Maybe. But back in the 60’s/70’s, I bet the life of the car was a lot less than what we expect now. I remember people bragging about making it to 100k in their - insert brand.

Torsion Bars should always be replaced as a pair. Obviously if one is broken then replace. If the splines are badly worn from metal to metal, safe to say, replace....if you are seeing metal to metal wear anywhere on the bar except at the splined ends, you have other issues going on as well, so replace the bars but look further at other components.

Bushings cause bar wear on the shaft