Swing Arm Guides

[lionel vargas]

If anything it seemed better when I had it about an inch lower, but either way it was little difference. My torsion bars seem fine and adjusted out with plenty of travel either way. The ride is plenty if not excessively firm up front. But you could have a point. I also have a front spoiler/ airdam and the fiberglass bumper covers. This must change the flow a bit.
--
Lionel Vargas
73 260 CCL
FL Keys

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[Rdenney]

Hardie Johnson writes...

> Also could it be your torsion bars have gone soft over time?

In the bicycle world, there is a myth that bicycle frames go soft over
a period of years with heavy use. It has been fully debunked. The
stiffness properties of steel do not change over time, or with load.

What does change is the strength, with work hardening, if the stress
is anywhere close to yield strength. But that should not have any
effect on torsion bars.

And steel that is excessively loaded, damaged by external trauma, or
that was improperly tempered may get brittle and develop fatigue
cracks. A crack isn't strong or stiff at all, and I think that's is
what is behind the perception that it has gone soft. Any part that has
lost rigidity because of fatigue cracks needs to be replaced
immediately, particularly if it's the only thing holding up the coach,
heh, heh.

I've seen reports of torsion bars that have sagged over time. I don't
think they are any softer than they were, they have just yielded a
little here and there as a result of a particularly bad bump. Or they
are cracking from fatigue. If the former, they can be readjusted. If
the latter, they need to be replaced.

Rick "thinking we'd be in real trouble if steel goes soft over time"
Denney

'73 230 Ex-Glacier "Jaws"
Northern Virginia

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[hardie johnson]

> Hardie Johnson writes...
> > Also could it be your torsion bars have gone soft over time?
> The stiffness properties of steel do not change over time, or with load.
> I've seen reports of torsion bars that have sagged over time. I don't think they are any softer than they were, they have just yielded a little here and there as a result of a particularly bad bump. Or they are cracking from fatigue. If the former, they can be readjusted. If the latter, they need to be replaced.
A friend's senior engineering thesis demonstrated that steel does not suffer from repeated cycles of fatigue even when twisted beyong 360* rotation as long as yield limits are not exceeded. Give that, I am not sure how the bar itself would fail or sag over time. Maybe it is the brackets and arms that distort slightly. It does not take a lot of distortion in the spline area to drop the coach noticeably.
"Crashj, who is obviously not a man of steel"


--
Hardie Johnson "Crashj"
1973 26 foot Glacier, White Thing
Enola PA

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[Rdenney]

Hardie Johnson writes...

> A friend's senior engineering thesis demonstrated that steel does
> not suffer from repeated cycles of fatigue even when twisted beyong
> 360* rotation as long as yield limits are not exceeded. Give that, I
> am not sure how the bar itself would fail or sag over time. Maybe it
> is the brackets and arms that distort slightly. It does not take a
> lot of distortion in the spline area to drop the coach noticeably.
> "Crashj, who is obviously not a man of steel"

In theory, you are correct--the fatigue limit of steel (unlike
aluminum) is usually above the yield stress. But don't assume that in
the real world you know what the stress really is. Residual stress is
the usual culprit in fatigue, and that is usually result of forming
processes. For example, bicycle mechanics who know what they are doing
realize that steel spokes, when formed at the ends, have residual
stresses that will allow microscopic bits in the cross-section to
yield even when the overall part does not yield. They know to relieve
those stresses by momentarily overstressing the whole spoke after
wheel assembly so that the material around the residual stress peak
yields enough to relieve the peak.

Plus, any nick or bit of corrosion can also cause a stress riser that
yields, fatigues, and then starts a crack. Once the crack is started,
it will keep going becuase nothing is a bigger stress riser than the
tip of a crack.

I can see where a torsion bar with a slight residual defect could have
enough residual stresses to cause fatigue failures, especially if the
spring has been traumatized.

Rick "who suspects the pork chop may be a bit more ductile, however"
Denney

'73 230 Ex-Glacier "Jaws"
Northern Virginia

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[lionel vargas]

I refuse to add anything to the list of things I am worried about. Torsion bars are not one of them. My torsion bars are fine. My Torsion bars are fine. My ,,,,,,,,,
--
Lionel Vargas
73 260 CCL
FL Keys

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