Getting Hitched

Getting Hitched
ISSUE 03.2014
Getting Hitched
A
trailer hitch is an accessory that’s often
installed on most pickup trucks and
SUVs. Having a hitch on the back of a vehicle
opens up a whole new world of possibilities
for both practicality and fun.
Hitches are also a popular accessory
for many mid-sized CUVs, vans, minivans
and cars. These tend to be lighter-duty
applications for pulling small trailers or
for attaching accessories such as a bike or
cargo carrier.
Installing a trailer hitch is a fairly simple
job on many applications, and can usually be
done in 30 minutes or less. So here are some
suggestions to keep in mind when doing a
hitch installation:
First, you need to establish what your
customer wants to tow (and how often). The
weight of what’s being towed will determine
the class of hitch that will be required to
handle what they want to tow.
Second, you need to determine the
rated towing capacity of the vehicle. This
can usually be found in the vehicle owner’s
A trailer hitch adds the ability to tow all kinds of things, and gives a vehicle
an added dimension of utility.
manual or on a build plate in the door
frame. A vehicle’s rated towing capacity
is based on the engine, cooling system,
transmission, driveline, suspension and
tires, and the combined weight of the trailer
and vehicle.
CAUTION: If a
vehicle’s rated towing
capacity is not high
enough to handle an
anticipated towing
load, it’s not safe to
tow it. Exceeding the
rated towing capacity
risks damaging the
vehicle’s transmission
or driveline. The
brakes and suspension
may also be overloaded
and create a potentially
unsafe driving
Hitches are rated by weight capacity and design.
situation. Also, the
Class Ratings
Class I trailer hitches can handle a Gross
Trailer Weight (GTW) of up to 2,000 lbs.,
and a maximum tongue weight of 200 lbs.
The hitch may be a simple drawbar or step
bumper type of hitch. Class I receiverstyle hitches typically have a 1-1/4 x 1-1/4
inch square receiver and are fitted with a
continued inside
} Wiring
} ClassBasics
Ratings
} Bad
Wiring & Connectors
} Braking
} Tech Tips:Electrical Problems
} Diagnosing
} Wiring a Wiring Connector
} Replacing
} Circuit
} HitchTests
BallsWith a DMM
} Intermittent
Wiring
Faults
} Trailer Hitch
Installation
} Trailer Hitch Types
} Stability
Control
} Voltage
Drop
Testing
©2014 National Automotive Parts Association
engine may overheat because it lacks the
cooling capacity to handle the increased
load. These are all important considerations
that must not be overlooked.
Third, assuming the vehicle can handle
the anticipated load, you need to match the
hitch to the application — Class I or II hitch
for light-duty towing, a Class III hitch for
medium-duty towing, or a Class IV or V
hitch (or a bed-mounted fifth wheel hitch)
for heavy-duty towing.
} Towing Upgrades
} Review Questions:
TECH
tips
m Trailer electrical connectors
mounted on the rear bumper
or back of a vehicle usually
have a spring-loaded cover
to protect the connector from
the elements. Even so, dirt
or corrosion may foul the
connector preventing it from
making good electrical contact
with a trailer. The connector
can be cleaned with aerosol
electronics cleaner. If the
connector is heavily corroded
or damaged, or the pins fit
loosely, replace it.
m When figuring the maximum
towing capacity of a vehicle,
the factory rating should be
decreased by the weight of any
additional cargo in the vehicle,
the driver and additional
passengers.
m Little Known Fact You Should
Know: The factory-rated towing
capacities for many vehicles
may be overstated because
they are based on using a
weight-distributing hitch, not
a standard hitch. A standard
hitch may reduce the claimed
towing capacity as much as 40
to 50 percent in some cases.
m Some pickup truck
manufacturers recommend
using a sway control system if
towing a trailer weighing more
than 2,000 lbs. However, a
sway control system may not
be compatible with a trailer
that has a mechanical surge
brake because it may interfere
with the operation of the brake.
Some weight-distributing
hitches may also interfere with
the proper operation of a trailer
surge brake.
1-7/8 inch ball. This type of light utility hitch
is good for the occasional user who wants
a hitch installed on a front-wheel drive car,
minivan or CUV.
Class II trailer hitches are for loads of up
to 3,500 lbs. GTW and 300 lbs. tongue weight,
such as a small boat trailer, snowmobile trailer,
motorcycle trailer or camper. Typical installation
applications include rear-wheel drive cars, CUVs,
full-size vans, pickups and SUVs.
Class III trailer hitches can handle up to
5,000 lbs. GTW and 500 lbs. tongue weight.
This is the most common general purpose
medium-duty hitch for pickup trucks, SUVs
and fullsize vans, and usually has a 2-inch
square receiver with a 2-inch or 2-5/16-inch
ball. This type of hitch usually attaches to the
vehicle frame, but may be bumper mounted if
a truck has a bumper that is strong enough to
handle it.
Class IV trailer hitches are for loads up to
10,000 lbs. GTW and 1,000 to 1,200 lbs. of tongue
weight, and is usually a “weight-distributing”
trailer hitch that mounts to the vehicle frame.
This type of hitch may have a 2-inch or 2-1/2 inch
receiver with a 2-5/16-inch ball.
Class V trailer hitches are for extra heavy loads
greater than 10,000 lbs. GTW and more than 1,200
lbs. tongue weight. This type of trailer hitch will
usually be a weight-distributing hitch with a 2-1/2
inch or 3-inch receiver with a 3/4-inch pinhole.
Typical uses might be to tow a car trailer, larger
camper, boat or livestock.
Custom trailer hitches are designed
for specific vehicle applications and
are usually easy to install.
For really heavy towing, a Fifth Wheel trailer
hitch or a Gooseneck trailer hitch that mounts in
the bed of pickup truck may be required. A bedmounted fifth wheel hitch is recommended for
loads heavier than 10,000 lbs. GTW. Some of these
hitches can handle loads up to 20,000 lbs. or more,
and are designed to pull large campers, vehicle
trailers or livestock.
WARNING: NEVER exceed the rated towing
capacity of the hitch or trailer. Overloading a hitch
or trailer may cause the hitch to fail.
When choosing a hitch, consider not only your
customer’s current towing needs, but also their
future needs. If they are towing a rowboat today,
they might trade up to a larger, heavier bass boat
next year, or a larger camper or whatever. The
point is to recommend a hitch that will satisfy their
current and future towing needs. For many pickup
trucks and SUVs, that would mean a Class III or
IV trailer hitch rather than a light-duty Class I or II
trailer hitch.
A bed-mounted fifth wheel adds a lot of towing capacity, and may be required
for extra heavy loads.
ISSUE 03.2014
Getting Hitched
15 percent to prevent overloading the hitch.
For larger Class V fifth wheel bed-mounted
trailer hitches, up to 25 percent of the weight
can be placed on the hitch.
Hitch Balls
A weight distributing hitch uses
leverage to shift a trailer’s weight
from the tongue to the vehicle
chassis, and is usually required
to achieve the maximum rated
towing capacity.
Trailer Hitch Types
In addition to the various weight
classifications, a hitch will be classified
as either a simple weight-carrying
(“deadweight”) hitch or a weightdistributing (“equalizing”) hitch. Weightcarrying hitches are typically used for
smaller, lighter loads (under 5,000 lbs.
GTW) while weight-distributing hitches are
generally recommended for larger, heavier
trailers over 5,000 lbs.
A weight-distributing hitch has an
attachment that slides into the receiver to
redistribute the weight on the tongue. The
hitch uses a pair of spring bars (one for each
side of the trailer) to lift and apply leverage
to the tow vehicle. This redistributes tongue
weight from the tongue to the vehicle to help
level the back of the vehicle and the front of
the trailer for improved stability while towing.
The trailer tongue load should be kept
between 10 to 15 percent of the loaded
trailer weight for weight-carrying hitches
and weight-distributing hitches. The tongue
should carry at least 10 percent of the weight
for good towing stability, but no more than
Trailer hitch balls come in various sizes
(1‑7/8, 2 and 2-5/16 inch). The diameter of
the ball obviously has to match the coupler
on the trailer, so having more than one ball
size is usually a good idea if a vehicle is used
to tow different trailers (which may or may
not have the same sized coupler).
Balls may be chrome plated, plain or
stainless steel. A cover can help protect the
ball when it is not being used. The ball can
be greased to reduce friction when towing.
Stability Control
Trailers sometimes have a tendency to sway
back and forth as they are being towed
down the road, especially if there are strong
crosswinds. As the swaying increases, it can
create an unstable and difficult to control
situation for the driver. A Sway Control
system can reduce the sideways (lateral)
movements of the trailer to restore handling
stability. Most use friction sway control bars
that slide in and out to dampen the lateral
motions of the trailer.
On some new Ford and Dodge Ram
pickups, the trucks use electronic sway
control to improve towing stability. The
truck uses a combination of its own ABS/
Stability Control system with the electric
brakes on the trailer to maintain control.
This hitch is equipped with a sway
control system to help stabilize
the trailer.
Braking
This ball assembly has all the sizes
covered. Just rotate the bar in the
receiver to use a different size.
Rules vary from state to state, but trailer brakes
are often required on trailers that weigh more
than 1,500 lbs. GTW. Smaller utility trailers
are usually light enough that the vehicle’s own
brakes are adequate, but for heavier loads the
axles on the trailer are equipped with their
own brakes to share the braking load.
There are two types of trailer brakes:
hydraulic “surge” brakes that use the trailer’s
momentum to apply the brakes when the
tow vehicle brakes, or electric brakes that
are wired into the vehicle’s electrical system
and apply the brakes in conjunction with
the vehicle’s brakes.
Most larger trailers and fifth wheel trailers
have electric brakes, activated by a controller in
the tow vehicle. The controller automatically
coordinates the tow vehicle and trailer braking
so the two systems work together when the
brake pedal is applied. The controller can also
be helpful in stabilizing a trailer that sways
because of bad road conditions. Manually
applying the trailer brakes by using the hand
lever on the controller can stabilize a trailer that
is starting to sway.
Breakaway switches are also required for
trailers over 1,500 lbs. GTW. The breakaway
switch activates the trailer brakes if the trailer
comes loose from the vehicle. Safety chains
are also required on all trailers as a fail-safe
should the hitch separate from the vehicle.
Wiring
Wiring can be tricky if a vehicle is not
factory-equipped with an electrical
connector for a trailer. There are basically
three types of connectors: 4-pin (for taillights,
brake lights and turn signals), and 6 or 7-pin
for lights and electric trailer brakes.
If a trailer is equipped with electric
brakes, your customer will need a 6 or 7-pin
electrical connector. If it is a small utility
trailer with no brakes, or a trailer with
hydraulic surge brakes, it will only require a
4-pin connector.
On older vehicles, installing a trailer
electrical connector involves wiring the
connector into the taillight wiring harness.
You locate the correct wires for the taillights,
brake lights and turn signals, then make
the connection using crimp-on connectors
or splicing the appropriate wires together.
Referring to the vehicle’s wiring diagram can
help avoid mix-ups.
continued on back
With newer vehicles, it’s more complicated
because the wiring is integrated in the vehicle
and harder to splice. This often requires a
more sophisticated trailer connector that
includes a plug-in style harness. Simple plugin harnesses that allow easy installation are
available for most new trucks today.
Once the electrical connector has been
installed, hook up the trailer and make sure all
of the lights are working properly BEFORE your
customer hits the road. Also, test the brakes to
make sure the trailer brakes are responding and
the trailer is braking evenly. Uneven braking or
no braking would indicate an electrical problem
requiring further diagnosis.
Towing Upgrades
Towing puts added strain on the engine,
transmission, driveline, brakes and
suspension, so various upgrades may be
recommended to improve a vehicles’ towing
capacity as well as handling stability.
If a vehicle has an automatic transmission,
the original equipment ATF cooler may be
marginal for heavy or prolonged towing. The
factory ATF cooler may be mounted in the
radiator, or a separate cooler may be necessary.
Installing a larger ATF cooler can help keep
ATF temperatures down to prolong the life of
the transmission.
If a vehicle is operated in a hot
climate and will be used for heavy towing
(and is not factory-equipped with a
towing package), the cooling system
can be upgraded by replacing the stock
radiator with a more efficient radiator.
Recommending a coolant additive that
increases heat transfer can also help
keep engine temperatures under control.
Installing a lower temperature thermostat
is NOT recommended because the engine
control system relies on a fixed operating
temperature for fuel and emissions control.
Upgrading the lubricants in the
differential to a full synthetic can help reduce
driveline friction, differential temperatures
and wear when towing.
To help keep a vehicle level and improve
handling and steering stability when towing,
installing suspension aids such as overload
shocks/springs, air springs and/or a rear sway
bar can provided much needed improvement.
Other accessories that may be needed
when towing include larger side mirrors for
improved rearward visibility, an extra jack
(scissor jack, hydraulic bottle jack or small
lightweight floor jack) and safety stands for
emergency roadside tire changes should a
trailer tire go flat. Reflective safety signs or
LED safety strobes, and/or emergency rear
lighting can also be a lifesaver should the need
arise. Auxiliary rear lighting is also a plus for
making after dark trailer connections, and
a small rearview video camera mounted on
the back bumper can make hooking up to a
trailer an easy, one-person job.
Trailer Hitch Installation
Most aftermarket trailer hitches are custom
designed to fit a particular vehicle application,
though “universal” hitches are also available
to fit a wider range of applications. Most
custom hitches can be easily installed within
30 minutes or less.
When installing a trailer hitch, make sure
the hitch clears all suspension components, the
spare tire (if hung underneath) and the tailpipe,
and is securely attached to the vehicle. Follow
the hitch supplier’s installation instructions and
use the fasteners that are provided.
If installing a universal type of hitch
that requires welding, grind off any paint or
undercoating from the areas where the welds
will be made to assure good weld penetration
and strength. After the welds have been
made, paint or undercoat the welds for
corrosion protection.
CAUTION: Make sure there are no fuel
leaks when welding, and that the welding
arc or flame is kept away from any fuel lines,
brake lines, gas tank vent lines or wiring.
This fifth wheel gooseneck hitch
has reinforcing bars to distribute
weight across the truck bed.
Measure the position of the hitch carefully
to make sure it is centered.
If installing a fifth wheel hitch, the center
load point of the hitch must be forward of the
vehicle’s rear axle.
The final step when installing a hitch is to
figure out the proper ball height for the trailer.
The final location of the ball should be such
that the trailer will sit level when it is attached
to the vehicle.
Level the trailer, then measure from the
ground to the inside top of the coupling
on the trailer. Then measure the distance
from the ground to the hitch or receiver to
determine where the ball needs to be. Use
these measurements to determine how much
drop or rise is needed in the ball mount so the
trailer will be level.
Review Questions March 2014:
1. The most common hitch class
for general towing is:
2. A 2-inch square receiver is
typically used on:
3. A vehicle’s maximum towing
capacity depends on:
a. Class I
b. Class II
c. Class III
d. Class IV
a.
b.
c.
d.
a. The gross weight of the trailer
b. T he combined weight of the
trailer and vehicle
c. T he vehicle’s engine,
transmission, driveline, brakes,
suspension and tires
d. A
ll of the above
Answers: 1. c, 2. c, 3. d
Class I hitch
Class II hitch
Class III hitch
Class IV hitch
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