QUOTE(mepstein @ Jun 7 2021, 07:02 AM)
I think it’s a weak spot from corrosion or rubbing that does them in.
Corrosion creates a stress riser. Highly stressed steel abhors a stress riser.
QUOTE(jim_hoyland @ Jun 7 2021, 07:56 AM)
Can they be tested in the car ?
No.
They are either working or they are broken. Sag is hard to detect since the torsion bars can be adjusted so sag gets offset over time. Torsion bar is also less prone to sag than a coil spring by virtue to the shorter length of spring steel used in a torsion bar and the larger diameter of the steel.
When I took the bars out of mine, they had some serious pitting. Still were functional at the time of removal but they will not be going back into my vehicle. Too much risk of them breaking in the future. Always happens at the worst time. Time for new parts.
QUOTE(930cabman @ Jun 7 2021, 06:57 AM)
Every motion of a torsion bar introduces stress, after how many cycles can this thing last? I am sure with quality steel these last a long time, but 1/2 century and still rolling.
Life of a spring is not measured in time.
Spring life is measured as # of cycles of full reversal between two load conditions. Would be measured on the order of # of millions of load reversals.
As noted above by Mark, corrosion, nicks, and worn in rub points resulting from from worn bushings are leading cause of death for torsion bars.