Suspension and shock absorbers

[Ed Price]

I was talking with an off-roader the other day, describing the Amphi's
suspension system. After sketching out some of the parts, he asked me where the
safety cable is attached. He was aghast to find out that Amphis don't have any
safety cables.

So, what's a safety cable? It's a heavy duty strap, or aircraft grade cable,
that limits the extension of a vehicles suspension. When an off-roader goes
airborne at the crest of a hill, his wheels all drop as low as they'll go. If
you don't have a safety strap, then the only thing that stops the drop of the
wheel is the shock piston hitting the top of the shock body. Shocks aren't
designed to catch the entire unsprung weight of the wheel, so the safety straps
are installed to protect the shocks.

So now, I'm wondering about the Amphi shocks. True, we rarely get airborne, but
the wheels do drop to full extension when we swim. Maybe it's a non-issue with
Amphis, since the weight of a wheel is less in water, and the shocks only take a
jolt one time as we enter the water. But even so, it's a bad thing to do to your
shocks.


Ed
El Cajon
67 Rust Guppy


[Non-text portions of this message have been removed]

 

[Gary Grieshaber]

That's a good point Ed! I had an axle drop out of the tranny once, the
car didn't move much after that! Years ago I had safety straps on the
rear suspension of a '61 VW I used to race (rally style) so the wheels
wouldn't "fold under" on the corners. I'm sure they couldn't hurt. Gary.

> I was talking with an off-roader the other day, describing the
Amphi's suspension system. After sketching out some of the parts, he
asked me where the safety cable is attached. He was aghast to find out
that Amphis don't have any safety cables.
>
> So, what's a safety cable? It's a heavy duty strap, or aircraft grade
cable, that limits the extension of a vehicles suspension. When an off-
roader goes airborne at the crest of a hill, his wheels all drop as low
as they'll go. If you don't have a safety strap, then the only thing
that stops the drop of the wheel is the shock piston hitting the top of
the shock body. Shocks aren't designed to catch the entire unsprung
weight of the wheel, so the safety straps are installed to protect the
shocks.
>
> So now, I'm wondering about the Amphi shocks. True, we rarely get
airborne, but the wheels do drop to full extension when we swim. Maybe
it's a non-issue with Amphis, since the weight of a wheel is less in
water, and the shocks only take a jolt one time as we enter the water.
But even so, it's a bad thing to do to your shocks.
>
>
> Ed
> El Cajon
> 67 Rust Guppy
>
>
> [Non-text portions of this message have been removed]
>
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[rogtwo@aol.com]

On many cars and trucks, the shock absorbers are the only thing that limit
the travel of the suspension. Our Amphicars are not unique here, so I really
don't see a problem.

Since I modified new shocks to fit on the rear of my car, I can also say the
following about the small-spring assemblies: When the suspension is fully
extended, the springs are nearly slack. The total force on the shock from the
spring and the weight of the suspension is probably only around 100 pounds (this
may not apply to the larger springs or to the front).

Also, there's a huge difference between normal driving and driving where you
are regularly leaving the ground! It's not the static load of the axle
hanging from the shock that's going to break it, it's the dynamic loads that
will do
it. Keep in mind that the off-road vehicle probably has a solid axle and
large tires and wheels, weighing maybe 5 times what our Amphi suspension weighs.

I've off-roaded for years in a number of different vehicles (without safety
straps) and never broken a shock. If the guy you talked to is breaking shocks,
he's beating his rig really hard. Also, I suspect most shocks that are
broken off-road are actually broken during the landing, not the launch. If you
land hard on one wheel with a solid axle mounted on leaf-springs (especially
extra tall leaf-springs), the axle will tilt, twist and shift sideways a lot.
Even with the rubber bushings, this is going to apply some bending loads to the
shock. Add to this the very high forces of the sudden landing on a fully
extended shock, and you can start to see how one could break.

But, just because the shock breaks when the vehicle lands, doesn't mean the
safety straps are not necessary. Because -- the next bump is only 5 feet away
and with a now broken shock, the suspension will surely overextend as the rig
bounces over this bump if it doesn't have safety straps.

In short, safety straps are absolutely NOT necessary on your Amphicar unless
you plan on regularly going airborne off jumps with your car.

Roger

White '63
Seattle


[Non-text portions of this message have been removed]

 

[rogtwo@aol.com]

PS -- To add to my rant about shocks and safety straps:

Do to the somewhat thin metal of our Amphicar bodies (not to mention
corrosion), I am suspicious that the shock absorber might not be the week link.
If
you pulled hard enough on the shock to break it, I think it might rip out of the
top of the fender first. This makes the addition of a safety strap suspect
unless you find a way to more securely attach its top end to the car body.

And while I'm rambling on anyway, the shocks on Amphi's do break. On the
ones I saw, it appeared the failure was due to lack of oil. That is, it looked
like all the oil had leaked out long ago, robing the shaft of the shock of
lubrication. The shaft then wore against the body of the shock until it broke.
Note that a safety strap would not help in this situation. That's because the
real problem is not overextension, but instead collapse. Since the shock
holds the spring, when the shock breaks, the spring will probably bend and
"sproing" out (like that technical term ). I this happens on the back, that
corner of the car is going to ride a bit low!

So, if you are concerned about your shocks breaking, you time will be much
better spent checking your current shocks for oil than installing safety straps.
If your car bounces a lot, like the shocks are bad. You really should
replace them. It's not just a comfort issue, it's also a safety issue. If one
should break, you might loose control of your car. Even if your car rides OK,
you could still have a bad shock. If you have original shocks, you might want
to remove them and do this quick check. With the shock off the car, turn it
up-side-down and right-side-up a few times. If water drips or pores out of the
shock, guess what -- you need a new one! If you don't want to remove the
shock from the car, then you can remove the wheel and carefully examine the
shaft
and the seal area for wear. If you can see that the shaft has a step worn in
it, or that the seal area appears worn oval at all, then you need a new shock
BAD!

Roger


[Non-text portions of this message have been removed]

 

[John Friese]

On the other hand, these cars are 40 years old and there's never been
a problem in this area. Just how bad an oversite can this be?

John Friese



--- In amphicar-lovers@yahoogroups.com, "Ed Price" <edprice@c...> wrote:
> I was talking with an off-roader the other day, describing the
Amphi's suspension system. After sketching out some of the parts, he
asked me where the safety cable is attached. He was aghast to find out
that Amphis don't have any safety cables.
>
> So, what's a safety cable? It's a heavy duty strap, or aircraft
grade cable, that limits the extension of a vehicles suspension. When
an off-roader goes airborne at the crest of a hill, his wheels all
drop as low as they'll go. If you don't have a safety strap, then the
only thing that stops the drop of the wheel is the shock piston
hitting the top of the shock body. Shocks aren't designed to catch the
entire unsprung weight of the wheel, so the safety straps are
installed to protect the shocks.
>
> So now, I'm wondering about the Amphi shocks. True, we rarely get
airborne, but the wheels do drop to full extension when we swim. Maybe
it's a non-issue with Amphis, since the weight of a wheel is less in
water, and the shocks only take a jolt one time as we enter the water.
But even so, it's a bad thing to do to your shocks.
>
>
> Ed
> El Cajon
> 67 Rust Guppy
>
>
> [Non-text portions of this message have been removed]