I wrote\|>
\|> If it was perfectly rigid, it would also turn your rear axle housing
\|> into the world's biggest sway bar.
Scott Fisher wrote |
|Say... you're right! It would, wouldn't it? So what's that saying
|about how for every problem there is a solution that is simple,
|elegant, and wrong? :-)
George Jefferson writes\
\I'm not sure I understand this.
OK, here is what we are talking about. Scott suggested that if the front
half of an MGB leaf spring were inflexible, but properly jointed at only
its forward end, this section would prevent the rotation-and-release that
Hotchkiss leaf-spring cars suffer. This causes wheel hop in acceleration
and braking as each leaf spring winds itself into an S-shape and then
snaps back. Ask any early Mustang owner.
When the rear of the car is depressed, the axle would rotate slightly,
forward at the top. The problem is that as the car leans to the right,
the right end of the axle wants to rotate more than the left. This makes
the axle housing act as a sway bar. Cast-iron MGB axle housings are just
a tad too rigid for this purpose, so you would get very high roll
stiffness. I actually did something like this with a Cortina GT back in
the dark ages.
\Many 'modern' live rears are
\connected to the chassis with rigid links. They use coil springs,
\but I think you might achieve the same thing with your half leaf design.
\( of course, were it a really good thing to do, it could have been
\done in steel 20 years ago, no? )
The difference is that a 5-link live rear axle setup actually has joints
where the links hit the axle housing. The anti-twist action is gotten by
combination of two links, rather than a rigid lever-arm. The rubber in
the joints is enough to make up for the differences in the left and right
sides when the car leans. This system is lighter, too, because links that
take only extension/tension loads can be made much lighter than arms that
take bending loads. The four longitudinal links take no bending loads,
their rubber joints allowing the coil springs to take the vertical loads
and the Panhard rod to take the lateral loads of cornering. Most other
methods than the classic 5-link operate on similar principles.
There is a use of the "Scott Fisher" rigid-arm design though. An example
is my FWD Mighty K-wagon. On each side is a trailing arm which is
rigidly welded to a dead axle formed by a piece of channel. As the car
leans to the right, the right end of the channel rotates more than the
left, causing the channel to twist, acting as a sway bar. Chrysler wanted
more roll stiffness than the channel provided, so there is actually a
round piece of torsion-bar material (a real sway bar!) tucked inside the
channel. People who want even more roll stiffness in this design have
been known to clamp a sway bar onto the arms, with the torsion section
running along the axle, or just to bolt more meat onto the open bottom of
the channel. The trailing arms are only stressed in bending by the sway
bar action, as the vertical loads are taken by the coil springs and there
is a Panhard rod (called a "track bar" by USA manufacturers reluctant to
give credit to foreigners) to take the lateral loads.
Volkswagen went the other way with this on the Rabbit (Golf for OFATP),
using the rear sway bar as the pivot points for trailing arms which do all
the location. These arms need to be stronger, as they take bending loads
for the swaybar action, braking, and the lateral loads of cornering. Only
the vertical loads are taken by the coil springs, and maybe not all of
them. I am a little fuzzy on where the springs connected to the trailing
arms. I am not nuts about the effective camber change that this system
gives, but at least the wheels point straight ahead. I imagine they stole
much of this from the Mini, but the front of a Beetle is somewhat similar.
This stuff is all so simple, compared to the Europa IRS, which has had us
scratching our heads and arguing on the Lotus list. And I have still not
figured out all the ins and outs of the second-generation RX-7 IRS rear!
Phil Ethier, THE RIGHT LINE, 672 Orleans St, Saint Paul, MN 55107-2676
h (612) 224-3105 w (612) 298-5324 phile@stpaul.gov
"There is nothing like a complete money-is-no-object restoration.
And this is going to be nothing like one." - Phil Ethier
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