Having taken a few <g> of these shocks apart, I can maybe help
this discussion. The leaks that befall these Armstrong levers occur at the
shaft where it passes though the seal. The original seal is more of a thick
solid rubber washer, maybe 1/2" thick. It is retained in the shock body by
a tin washer crimped in the body. Pretty low-tech sealing. Not an oil seal
as one would expect (radial lip type). Ever wonder why your owner's manual
suggests topping-up as a regular scheduled maintenance procedure? I would
suggest it is because they expect the shock to leak. These shocks also have
no bearing for the shaft to rotate in beside the cast metal body. We see
cases where the shaft has become pitted from oil/salt/water being packed in
that area. Naturally, when that happens the seal does even less, and the
oil exits even faster. So, a weak seal design allowing the egress of oil
and the ingress of grit to both the bearing surface and beyond seems to me
to be the most limiting feature of these shocks.
As far as side forces, besides crashing the car, there doesn't
seem to be much evidence of the kind of wear I would expect with side
forces. There isn't much in the way of thrust washers or surfaces.
A few other thoughts on the non-technical side. Certainly cost is
a primary reason for tube shocks. Much cheaper to make. Much cheaper to
make the variations from one make to another. Macpherson struts have those
positives as well as they are supplied more easily in subassemblies with
engines and transaxles going in as one lump. Tube shocks do leak, and more
often than they are noticed. BTW, early 60's Ford Anglias had MacPherson
struts on the front and good ol' levers on the back.... how's that for
clashing technologies.
Obviously I am an advocate of lever shocks being in the cars for
which they are designed (I wouldn't add them to my Camry). I know that the
ability exists to overcome the shortcomings of these Armstrong shocks.
I apologize for being so longwinded I've been writing this while
answering many phones.
I'd appreciate any feedback. Peter C. I gotta go put out a
fire. Later
----
At 01:16 PM 6/9/2000, Michael Lupynec wrote:
>Max is right on most counts and I leave the calculation of the
>lever shock valve amplification problems to the Hydraulic gods.
>
>But the lever does not support any of the weight of the car. It
>does however take some smaller share of lateral road forces thru
>the bushings (that the lever is mounted in) and yes this is
>exactly where most lever shocks fail - in the leak mode.
>
>The Macpherson strut or tube shock works on a well located A arm
>and is spared the side forces.
>
>Mike L.
>60A,67E,59Bug
>
>----- Original Message -----
>From: Max Heim <mvheim@studiolimage.com>
>To: MG List <mgs@autox.team.net>
>Sent: June 9, 2000 1:41 PM
>Subject: Re: Fw: Tube shock conversion data
>
>
> > Actually, the feature of lever shocks which I always found
>dubious was
> > their mechanical "dis-advantage", so to speak. On the long end
>of the
> > lever you have the weight of the car, and all the forces acting
>upon it.
> > On the short end you have this tiny little valve body. The
>forces on the
> > valve body as amplified by the long lever arm must be enormous.
> > Conversely, any action produced by the valve body (i.e. damping)
>is at an
> > enormous mechanical disadvantage vis-a-vis the rest of the car.
>In
> > comparison, the forces on the tube shock are operating "straight
>through"
> > the axis (or slightly deflected if it is not mounted absolutely
> > perpendicularly), with no leverage advantage either way. This
>probably
> > enables lower internal hydraulic pressures, which would explain
>why leaky
> > tube shocks are rare, but leaky lever shocks are normal. But it
>also
> > suggests that tube shocks, with longer travel and lower
>pressures, could
> > be designed to have more subtle, even non-linear, damping
>action.
> >
> > All of the above is pure speculation, of course... <g>
> >
> > >
> > >In a message dated 6/8/00 8:09:45 PM Eastern Daylight Time,
>yd3@nvc.net
> > >writes:
> > >
> > ><< I believe I have read somewhere that the there are several
> > > reasons most vehicles went to tube shocks.
> > >
> > > 1) cost:
> > >
> > > 2) response: To my mind, the lever shock would have more play
> > > between jounce and bounce because of the design and rocking
> > > factor. It would be similar to determining TDC in an engine.
>A
> > > piston could be TDC while the crank could be rotated a few
> > > degrees with showing any piston movement. Thus the lever has
> > > some "dead" spots between jounce and bounce.
> > >
> > > 3) heat: I would think the tube shock is less sentive to heat
> > > retension.
> > >
> > > 4) travel: I would think the tube shock's greater travel would
> > > produce more uniform results. >>
> > >
> >
> >
> > --
> >
> > Max Heim
> > '66 MGB GHN3L76149
> > If you're near Mountain View, CA,
> > it's the red one with the silver bootlid.
> >
> >
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