Shock Absorbers & Springs, Front

E

Ed Price

Guest
So I'm having a close look at my 40-year-old front shocks. I decided to remove
the spring from around the shock, and found out several interesting things:

1. The spring has no "pre-load", that is, with the shock off the Amphi, the
spring pushes the shock rod out to full extension. But at full extension, there
is no more "push" (compression) left in the spring.

2. The "eye" mount at the top is just threaded onto the male-threaded shock rod.
Once you can get a vise-grip pliers in through the spring coils, and grab the
shock rod, you can unscrew the eye off of the rod. The upper spring seat, and a
somewhat conical locating stub then will just slip off the shock rod, followed
by the spring.

3. You can thus take this whole thing apart, without fear that the spring will
hop across your garage or modify your hairline. Note that the vise-grip will
likely score the polished rod, so this is really a one-way operation. You don't
want to use a shock that has a scored or burred rod!

4. My shock had a layer of rust on the top 2/3 or so of the rod length. That
tells me that the bottom 1/3 was within the shock when my Amphi sat for all
those years. That tells me my Amphi normally compresses the spring only about an
inch.

5. Now here, things get weird. The Amphi spring is 15 turns of 0.365" diameter
steel wire, which forms a coil 10.25" long with an OD of 2.5". When you plug
these values into the engineering spring equation, you get a calculated spring
rate of 180 pounds per inch. (That means that it takes 180 pounds to compress
the spring one inch; a load of 360 pounds will compress it two inches, etc.)

6. But the Amphi specs say that the front wheel loading is 564 pound (curb
weight) or 438 pounds (empty weight). Even 438 pounds loading would just about
squash a 180 pound 3.5" spring down all the way. Either the spring rate, or the
loading, isn't accurate. If my Amphi actually puts maybe 450 pounds on a front
wheel, this implies that my spring rate is really much more like 400 pounds per
inch.

7. I had bought a pair of the Maeco PK22K1 shocks from Surplus Center (see
previous posts). These shocks have been reported to work well on the Amphi
front, despite their having a spring which is 12 turns of 0.312" diameter wire
forming a 10.25" long, 2.25" OD coil. (Their rated spring rate is 200 pounds,
but I calculate only 150 pounds.) But a loaded Amphi would put 564 pounds on
this spring, and even with a 200 pound rate, it would squash it down 2.8" of the
available 3.5" of travel. And that's not good; hit a moderate bump, and you'll
bottom out on the spring.

I'm going to measure the spring rate, now that I have the coil handy. I'll let
you know what comes out of this obsession, but meanwhile, has anybody actually
weighed each corner of their Amphi?

Ed
El Cajon
67 Rust Guppy


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

rogtwo@aol.com

Guest
Ed,

It's good to here there is another anal engineer out there. :) :) :)

So, after reading your message, I went out and measured may car. Here's what
I found:

Spring OD 2.48"

Wire Diameter 0.36" including heavy paint. I'd guess the actual wire
diameter is about 0.35 inches.

Active coils - 13 or 13.5 (I didn't count the tapered end coils as they stack
when loaded)

Compression of shock when car weight is added - 1.45 inches (this is with
nothing in the trunk, not even the spare tire).

These numbers will give you significantly higher loads than you got with the
numbers you used.

But, that's not all -- Call now to get this one-time offer! :) :) :) :)

Most importantly, my spring has a small preload. I don't have scale here
that can measure the full weight on the front wheel, but may bathroom scale can
measure the preload. So, here's what I did:

I jacked up the front of the car and measured the spring length. Then I
stuck my bathroom scale under one tire and lowered the car a little. I lowered
it
until the spring measured about 1/16 inch shorter than the full shock
extension length.

Due to friction in the suspension, this measurement was not extremely
precise, but I got a load of about 200 pounds. This would include the preload
on the
spring plus the weight of the wheel, tire, brakes, axle, etc. (the un-sprung
weight). But, note that the spring never carries the un-sprung weight. So,
in the final analysis you need to subtract 200 pounds (per side) from the
listed weight for the front of the car.

The above numbers are just what I got. I don't claim they are correct for
other Amphis.

Roger St. John
White '63
Seattle


In a message dated 10/18/03 12:57:04 AM Pacific Daylight Time, wb6wsn@cox.net
writes:

> So I'm having a close look at my 40-year-old front shocks. I decided to
> remove the spring from around the shock, and found out several interesting
> things:
>
> 1. The spring has no "pre-load", that is, with the shock off the Amphi, the
> spring pushes the shock rod out to full extension. But at full extension,
> there is no more "push" (compression) left in the spring.
>
> 2. The "eye" mount at the top is just threaded onto the male-threaded shock
> rod. Once you can get a vise-grip pliers in through the spring coils, and
> grab the shock rod, you can unscrew the eye off of the rod. The upper spring
> seat, and a somewhat conical locating stub then will just slip off the shock
> rod, followed by the spring.
>
> 3. You can thus take this whole thing apart, without fear that the spring
> will hop across your garage or modify your hairline. Note that the vise-grip
> will likely score the polished rod, so this is really a one-way operation. You
> don't want to use a shock that has a scored or burred rod!
>
> 4. My shock had a layer of rust on the top 2/3 or so of the rod length. That
> tells me that the bottom 1/3 was within the shock when my Amphi sat for all
> those years. That tells me my Amphi normally compresses the spring only about
> an inch.
>
> 5. Now here, things get weird. The Amphi spring is 15 turns of 0.365"
> diameter steel wire, which forms a coil 10.25" long with an OD of 2.5". When
you
> plug these values into the engineering spring equation, you get a calculated
> spring rate of 180 pounds per inch. (That means that it takes 180 pounds to
> compress the spring one inch; a load of 360 pounds will compress it two
inches,
> etc.)
>
> 6. But the Amphi specs say that the front wheel loading is 564 pound (curb
> weight) or 438 pounds (empty weight). Even 438 pounds loading would just about
> squash a 180 pound 3.5" spring down all the way. Either the spring rate, or
> the loading, isn't accurate. If my Amphi actually puts maybe 450 pounds on a
> front wheel, this implies that my spring rate is really much more like 400
> pounds per inch.
>
> 7. I had bought a pair of the Maeco PK22K1 shocks from Surplus Center (see
> previous posts). These shocks have been reported to work well on the Amphi
> front, despite their having a spring which is 12 turns of 0.312" diameter wire
> forming a 10.25" long, 2.25" OD coil. (Their rated spring rate is 200 pounds,
> but I calculate only 150 pounds.) But a loaded Amphi would put 564 pounds on
> this spring, and even with a 200 pound rate, it would squash it down 2.8" of
> the available 3.5" of travel. And that's not good; hit a moderate bump, and
> you'll bottom out on the spring.
>
> I'm going to measure the spring rate, now that I have the coil handy. I'll
> let you know what comes out of this obsession, but meanwhile, has anybody
> actually weighed each corner of their Amphi?
>
> Ed
> El Cajon
> 67 Rust Guppy
>



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

Ken Chambers

Guest
Ed,

I'm the guy who reported those Maeco shocks for sale by Surplus Center and have
had them installed on my Amphi front end for almost two years now. They come
with only upper and lower horizontal bushings and bolt right in with only a
slight modification to the shock. The steel sleeve in the bushings need to be
drilled slightly larger from 7/16" to 12mm.

I'm quite satisfied with them especially given the attractive price of $20 each.
The Amphi sits perfectly level and rides fine too. They do, however, bottom out
when hitting large bumps but that hasn't produced any ill effects.

Ken Chambers, CA
'64 Red



> 7. I had bought a pair of the Maeco PK22K1 shocks from Surplus Center (see
previous posts). These shocks have been reported to work well on the Amphi
front, despite their having a spring which is 12 turns of 0.312" diameter wire
forming a 10.25" long, 2.25" OD coil. (Their rated spring rate is 200 pounds,
but I calculate only 150 pounds.) But a loaded Amphi would put 564 pounds on
this spring, and even with a 200 pound rate, it would squash it down 2.8" of the
available 3.5" of travel. And that's not good; hit a moderate bump, and you'll
bottom out on the spring.
>
> I'm going to measure the spring rate, now that I have the coil handy. I'll let
you know what comes out of this obsession, but meanwhile, has anybody actually
weighed each corner of their Amphi?
>
> Ed
 
W

WB6WSN

Guest
----- Original Message -----
From: rogtwo@aol.com
To: amphicar-lovers@yahoogroups.com
Sent: Saturday, October 18, 2003 10:12 AM
Subject: Re: [amphicar-lovers] Shock Absorbers & Springs, Front


Ed,

It's good to here there is another anal engineer out there. :) :) :)

So, after reading your message, I went out and measured may car. Here's what
I found:

Spring OD 2.48"

Wire Diameter 0.36" including heavy paint. I'd guess the actual wire
diameter is about 0.35 inches.

Active coils - 13 or 13.5 (I didn't count the tapered end coils as they stack
when loaded)

Compression of shock when car weight is added - 1.45 inches (this is with
nothing in the trunk, not even the spare tire).

These numbers will give you significantly higher loads than you got with the
numbers you used.

But, that's not all -- Call now to get this one-time offer! :) :) :) :)

Most importantly, my spring has a small preload. I don't have scale here
that can measure the full weight on the front wheel, but may bathroom scale
can
measure the preload. So, here's what I did:

I jacked up the front of the car and measured the spring length. Then I
stuck my bathroom scale under one tire and lowered the car a little. I
lowered it
until the spring measured about 1/16 inch shorter than the full shock
extension length.

Due to friction in the suspension, this measurement was not extremely
precise, but I got a load of about 200 pounds. This would include the preload
on the
spring plus the weight of the wheel, tire, brakes, axle, etc. (the un-sprung
weight). But, note that the spring never carries the un-sprung weight. So,
in the final analysis you need to subtract 200 pounds (per side) from the
listed weight for the front of the car.

The above numbers are just what I got. I don't claim they are correct for
other Amphis.

Roger St. John
White '63
Seattle


In a message dated 10/18/03 12:57:04 AM Pacific Daylight Time, wb6wsn@cox.net
writes:

> So I'm having a close look at my 40-year-old front shocks. I decided to
> remove the spring from around the shock, and found out several interesting
> things:
>
> 1. The spring has no "pre-load", that is, with the shock off the Amphi, the
> spring pushes the shock rod out to full extension. But at full extension,
> there is no more "push" (compression) left in the spring.
>
> 2. The "eye" mount at the top is just threaded onto the male-threaded shock
> rod. Once you can get a vise-grip pliers in through the spring coils, and
> grab the shock rod, you can unscrew the eye off of the rod. The upper spring
> seat, and a somewhat conical locating stub then will just slip off the shock
> rod, followed by the spring.
>
> 3. You can thus take this whole thing apart, without fear that the spring
> will hop across your garage or modify your hairline. Note that the vise-grip
> will likely score the polished rod, so this is really a one-way operation.
You
> don't want to use a shock that has a scored or burred rod!
>
> 4. My shock had a layer of rust on the top 2/3 or so of the rod length. That
> tells me that the bottom 1/3 was within the shock when my Amphi sat for all
> those years. That tells me my Amphi normally compresses the spring only
about
> an inch.
>
> 5. Now here, things get weird. The Amphi spring is 15 turns of 0.365"
> diameter steel wire, which forms a coil 10.25" long with an OD of 2.5". When
you
> plug these values into the engineering spring equation, you get a calculated
> spring rate of 180 pounds per inch. (That means that it takes 180 pounds to
> compress the spring one inch; a load of 360 pounds will compress it two
inches,
> etc.)
>
> 6. But the Amphi specs say that the front wheel loading is 564 pound (curb
> weight) or 438 pounds (empty weight). Even 438 pounds loading would just
about
> squash a 180 pound 3.5" spring down all the way. Either the spring rate, or
> the loading, isn't accurate. If my Amphi actually puts maybe 450 pounds on a
> front wheel, this implies that my spring rate is really much more like 400
> pounds per inch.
>
> 7. I had bought a pair of the Maeco PK22K1 shocks from Surplus Center (see
> previous posts). These shocks have been reported to work well on the Amphi
> front, despite their having a spring which is 12 turns of 0.312" diameter
wire
> forming a 10.25" long, 2.25" OD coil. (Their rated spring rate is 200
pounds,
> but I calculate only 150 pounds.) But a loaded Amphi would put 564 pounds on
> this spring, and even with a 200 pound rate, it would squash it down 2.8" of
> the available 3.5" of travel. And that's not good; hit a moderate bump, and
> you'll bottom out on the spring.
>
> I'm going to measure the spring rate, now that I have the coil handy. I'll
> let you know what comes out of this obsession, but meanwhile, has anybody
> actually weighed each corner of their Amphi?
>
> Ed
> El Cajon
> 67 Rust Guppy
>


Roger:

Thanks for some more numbers! I'm afraid I had some kind of a breakdown
yesterday, as my garage was about 105F, and I got pretty sick washing off
suspension parts in a MEK solvent bath. I wasn't even sure I had posted this
question on springs!

The replies so far have shown me making two mistakes. First, I had to learn how
to count the "active" coils. This isn't the total number of turns, but rather
should be done by starting where the fist turn begins to lift off the turn that
lays on the seat. You call this "turn #0". Then, you put a straight -edge on the
OD of the spring at this point, and now count the coils. The last coil likely
won't line up exactly, so you will have to make an estimate of what percentage
of a turn this is.

And the second error? Duhhh! I completely forgot about the unsprung weight! The
tire, wheel, spindle, bearings, brake drum, brake plate and shoes, and
oscillating arm are ALL unsprung weight. And an estimate of 200 pounds is likely
quite accurate. So that means the sprung weight, the weight carried by the
spring, is really more like 400 pounds maximum.

Anyway, since I now have all the pieces apart, I'm going to test the spring rate
on my springs this week.

BTW, for Chas Gould. The Amphi springs are linear. The only way to get a
progressive spring is to vary the wire thickness (difficult, but not
impossible), vary the turn spacing, or vary the coil diameter. Since the Amphi
springs have a constant diameter and pitch, and mine at least, have a constant
wire diameter, they aren't progressive springs. There's a whole bunch of spring
calculator sites on the web, such as:

http://www.racingpc.com/tips/coils-springs.htm

Ed
El Cajon
67 Rust Guppy


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

rogtwo@aol.com

Guest
Here are some technical comments on springs:

It was said: " ... the actual material employed in the spring has differing
tensile strength, and this may account for the variance of the manufacturers
ratings versus your calculation."

While different spring materials (steel, brass, fiberglass), will greatly
effect the rate of a given size spring, different types or strengths of steel
will have very little effect on the spring rate.

How can this be? The spring rate is based on how stretchy the steel is, not
how strong the steel is. The two are entirely different things.

The strength of the steel is obviously very important, if the steel is too
week, then the spring will just go flat, and not bounce back. It well be
permanently bent or flattened. Obviously this is no good. The spring MUST be
strong enough to hold the weight without permanently bending. The technical way
of
saying this is that the spring must operate within its "elastic" range.

Any steel that is within its elastic range will have about the same
stretchyness. The stretchyness is called the "modulus of elasticity", and for
steel
this has a value of about 28,000,000 to 30,000,000 lb/square inch. Thus, as
long as you are using steel springs, then the generic spring calculators should
give very good results.



Now, regarding variable rate springs: All of the methods mentioned (for coil
springs) rely on the number of active coils changing for the rate to change.


When the coil spacing is changed, the closer coils will stack first, reducing
the number of active coils. As the number of active coils decreases, the
spring gets stiffer. Likewise, if the coil diameter is varied, then the larger
coils will stack first, usually against a flat endplate. And if the wire
diameter is varied, the smaller diameter wire coils will stack first.

To repeat (with a metal coil spring) if the number of active coils doesn't
change, then the rate won't change.

Further, most springs are linear. Coil springs, leaf springs, and torsion
bars are all normally linear. Coils springs can be made nonlinear as mentioned.
Leaf springs can be made nonlinear by adding a leaf that is not always
active. This is often done by adding a flat leaf to the bottom of the spring
stack. When the spring is compressed enough, it contacts this additional leaf.

The only commonly used spring that is naturally nonlinear is a pneumatic
spring (air spring).

Roger
White '63
Seattle


In a message dated 10/19/03 2:38:50 PM Pacific Daylight Time, wb6wsn@cox.net
writes:

> BTW, for Chas Gould. The Amphi springs are linear. The only way to get a
> progressive spring is to vary the wire thickness (difficult, but not
> impossible), vary the turn spacing, or vary the coil diameter. Since the Amphi
springs
> have a constant diameter and pitch, and mine at least, have a constant wire
> diameter, they aren't progressive springs. There's a whole bunch of spring
> calculator sites on the web, such as:
>



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