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Leaf Springs
How
Leaf Springs Work
BY JOHN FULLER
Before
you start your towing trip, it's a good idea to go over a brief checklist --
for safety's sake.
You
take a good look in your mirrors, adjusting them correctly in order to see
passing traffic on the road.
You've
chosen the correct hitch and connected the towing vehicle to the trailer
properly.
The
brake lights and braking systems are working synchronously, assuring you of the
ride's legality.
With
everything loaded up, you're pretty confident the truck is ready for the job,
so you head out on the road toward your destination.
Once
you reach a steady speed, however, the trailer behind your truck starts to
bounce and sway a little more than it should.
Pulling
over to the side of the road, you rack your brains to figure out what you
missed. You start to wonder if your cargo weight is maybe too high -- but what
can you do about it?
In
this situation, if there's too much cargo weighing down a towed vehicle,
causing everything to rock and sway, the issue may be with the suspension.
If
a truck's suspension is too rigid, its wheels will often leave the pavement
after hitting bumps; a good suspension, on the other hand, keeps the wheels on
the ground as much as possible.
Many
towers use leaf springs to stabilize their towed load and to keep their cargo
grounded.
Although
you may not ever have heard about or even noticed leaf springs on larger tow
vehicles, the technology has been around for centuries and is one of the
earliest forms of suspension.
Even
Leonardo da Vinci used leaf springs in his diagram for a self-propelled car.
But how do they work?
Are
there different types of leaf springs? And how do you install them onto a
vehicle?
Choosing Leaf
Springs
Compared to most automotive technology currently
available, leaf springs don't
look too fancy.
Slightly
curved, they look a little like a metal bow from an archery set, except without
the string.
Leaf
springs come in several different varieties.
There
are monoleaf springs, or single-leaf
springs, that consist of simply one plate of spring steel.
These
are usually thick in the middle and taper out toward the end, and they don't
typically offer too much strength and suspension for towed vehicles.
Drivers
looking to tow heavier loads typically use multileaf
springs, which consist of several leaf springs of varying length stacked on
top of each other.
The
shorter the leaf spring, the closer to the bottom it will be, giving it the
same semielliptical shape a single leaf spring gets from being thicker in the
middle.
Leaf
springs also have different ends, depending on where they're connected to the
frame.
On double-eye leaf springs, the top plate --
and therefore the longest -- has both ends curved into a circle.
The
ends make two holes, which you can bolt to the bottom of a trailer's frame.
Open-eye
leaf springs have only one
"eye," or open hole. The other end of an open eye leaf spring can be
a hook end or a flat end.
Properly
installing leaf springs will ensure the best suspension for your tow vehicle;
read about leaf spring installation on the next page.
Installing Leaf
Springs
Leaf springs are positioned behind the wheel -- you
can't see them clearly when they're attached unless you crawl under the trailer
-- so the wheel needs to be taken off completely before installation begins.
Once
the wheel is off, you should notice a pair of hangers on either side of the
axle.
The
hangers are usually small, extended pieces of metal with holes that hang down
from the frame of the trailer.
Between
the holes of these hangers is where you line up the eyes of a leaf spring,
securing them with the proper hardware. If the leaf spring is a double-eye, one
hanger will have a shackle link.
Once
the leaf springs are bolted into the hangers, the next step is to install a
pair of U-bolts, two
horseshoe-shaped metal rods.
The
leaf springs can be overslung (placed
over the axle) or underslung (placed
under the axle).
Either
way, the U-bolts fit around the axle and secure to a metal plate that rests
against the leaf springs.
The
purpose of the U-bolts is to keep the leaf springs flush against the axle so
they take the weight of the cargo and don't move around too much during
driving.
It's
always important to check leaf springs and their accessories for wear -- a worn
or cracked leaf spring can cause untold damage to a trailer and its contents.
When
taking leaf springs off, it's a good idea to check the shackle links for wear.
A
round ring of wear that matches the shape of the nut is OK, but once the shape
becomes an oval, it's time to replace the shackle link.
Proper
care of leaf springs will ensure a safe ride while towing by keeping the
trailer's wheels on the ground and its cargo in place.
About John Fuller
John Fuller earned a bachelor’s degree in English from
the University of Georgia, where he also minored in film studies. After a brief
stint in film and television production, John began his career at HowStuffWorks
as a staff writer, writing about spacewalks, cave dives and everything in
between. He eventually switched to a position as editor, which is where you’ll
find him now. John also co-hosted the music podcast 'Stuff From the
B-Side' with publisher Mark Larson from 2008 to 2009, and he
currently contributes to “Stuff From the Future.'
John stands at his desk while he
works, which still gets him the occasional funny look from his coworkers. When
he’s not editing articles or eating too much free candy from the office, he
enjoys reading fiction, searching high and low for cheap (but quality) used
vinyl, playing basketball and watching baseball.
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