Lever
Centering
Springs (2)
Backing Plate

Magnet

Adjuster Spring
(hidden)
Adjuster Assembly

Adjuster Lever

Left Hand or Road Side Brake Shown

Note: Actuating lever should always wrap around front side
of axle, magnet wires should exit brake backing plate on
rear side of axle.

-10-

Forward self adjust electric brakes were introduced in October
of 1996. This feature adjusts the brakes on both forward and
reverse stops. Brake adjustment occurs when lining wear results in
enough gap between the shoes and the brake drum surface. This
added clearance will allow the adjuster mechanism to rotate the
screw assembly at the bottom of the brake. That action expands
the distance between the shoes and thus closes the gap to the
drum surface.

Brake Controllers
Electric brake controllers provide power to the magnets to
actuate the trailer brakes. Dexter offers a state-of-the-art inertial
controller called the Predator DX2®. This controller features an
accelerometer design which senses the deceleration of the towing
vehicle and sends a proportional voltage to the electric trailer
brakes. Other features include a visual gain setting for quick and
easy adjustment and a digital LED display to show the voltage
output. A manual override sends full voltage to the trailer brakes,
regardless of gain setting, for emergency conditions and also
illuminates the brake lights to warn of an impending stop.
Most electric brake controllers provide a modulation function
that varies the current to the electric brakes with the pressure
on the brake pedal or amount of deceleration of the tow vehicle.
Electronic or timing controllers do not provide proportional
modulation. These controllers tend to be inexpensive but not the
best choice for optimum braking. It is important that your brake
controller provide approximately 2 volts to the braking system
when the brake pedal is first depressed and gradually increases
the voltage to 12 volts as brake pedal pressure is increased. If
the controller “jumps” immediately to a high voltage output, even
during a gradual stop, then the electric brakes will always be fully
energized and will result in harsh brakes and potential wheel
lockup.

-11-

Braking Systems - Electric

Self Adjusting Feature (12¼" Brake Series Only)

How to Use Your Electric Brakes Properly
Your trailer brakes are designed to work in synchronization with
your tow vehicle brakes. Never use your tow vehicle or trailer
brakes alone to stop the combined load.
Your brake controller must be set up according to the
manufacturer’s recommendations to ensure proper
synchronization between the tow vehicle and the trailer.
Additionally, you may have to make small adjustments
occasionally to accommodate changing loads and driving
conditions.
Proper synchronization of tow vehicle to trailer braking can only
be accomplished by road testing. Brake lockup, grabbiness,
or harshness is quite often due to the lack of synchronization
between the tow vehicle and the trailer being towed, too high of a
threshold voltage (over 2 volts), or under adjusted brakes.

Braking Systems - Electric

Before any synchronization adjustments are made, your trailer
brakes should be burnished-in by applying the brakes 20-30
times with approximately a 20 m.p.h. decrease in speed, e.g. 40
m.p.h. to 20 m.p.h. Allow ample time for brakes to cool between
application. This allows the brake shoes and magnets to slightly
“wear-in” to the drum surfaces.

Trailer Wire Size Chart
Number
of Brakes

Hitch-to-Axle
Distance in Feet

2

Recommended
Minimum Hookup
Wire Size (Copper)
12 AWG

4

Under 30

12 AWG

4

30-50

10 AWG

6

Under 30

10 AWG

6

30-50

8 AWG

-12-

To ensure safe brake performance and synchronization, read the
brake controller manufacturer’s instructions completely before
attempting any synchronization procedure.

!

CAUTION

Before road testing, make sure the area is clear of
vehicular and pedestrian traffic. Failure to brake safely
could result in an accident and personal injury to
yourself and/or others.
Make several hard stops from 20 m.p.h. on a dry paved road free
of sand and gravel. If the trailer brakes lock and slide, decrease
the gain setting on the controller. If they do not slide, slightly
increase the gain setting. Adjust the controller just to the point of
impending brake lockup and wheel skid.
Note: Not all trailer brakes are capable of wheel lockup. Loading
conditions, brake type, wheel and tire size can all affect whether
a brake can lock. It is not generally considered desirable to lock
up the brakes and slide the tires. This can cause unwanted flat
spotting of the tires and could also result in a loss of control.
If the controller is applying the trailer brakes before the tow vehicle
brakes, then the controller adjustments should be made so the
trailer brakes come on in synchronization with the tow vehicle
brakes. For proper braking performance, it is recommended that
the controller be adjusted to allow the trailer brakes to come
on just slightly ahead of the tow vehicle brakes. When proper
synchronization is achieved there will be no sensation of the trailer
“jerking” or “pushing” the tow vehicle during braking.

-13-

Braking Systems - Electric

Synchronizing Your Trailer Brakes

General Maintenance - Electric Brakes
Brake Adjustment
Most Dexter 12¹⁄₄" electric brakes have a self adjusting feature. If
manual adjusting is required, use the following procedure:
Brakes should be adjusted (1) after the first 200 miles of operation
when the brake shoes and drums have “seated,” (2) at 3,000 mile
intervals, (3) or as use and performance requires. The brakes
should be adjusted in the following manner:
1. Jack up trailer and secure on adequate capacity jack stands.
Follow trailer manufacturer’s recommendations for lifting and
supporting the unit. Make sure the wheel and drum rotates
freely.

!

CAUTION

Braking Systems - Electric

Do not lift or support the trailer on any part of the
axle or suspension system. Never go under any trailer
unless it is properly supported on jack stands which
have been rated for the load. Improperly supported
vehicles can fall unexpectedly and cause serious injury.
2. If equipped, remove the adjusting hole cover from the
adjusting slot on the bottom of the brake backing plate.
3. With a screwdriver or standard adjusting tool, rotate the star
wheel of the adjuster assembly to expand the brake shoes.
Adjust the brake shoes out until the pressure of the linings
against the drum makes the wheel very difficult to turn.
4. Then rotate the star wheel in the opposite direction until the
wheel turns freely with a slight lining drag.
5. Replace the adjusting hole cover and lower the wheel to the
ground.
6. Repeat the above procedure on all brakes. For best results,
the brakes should all be set at the same clearance.

-14-

Your trailer brakes must be inspected and serviced immediately if
a loss of performance is indicated. With normal use, servicing at
one year intervals is usually adequate. With increased usage, this
work should be done more frequently as required. Magnets and
shoes must be changed when they become excessively worn or
scored, a condition which can reduce vehicle braking.
Clean the backing plate, magnet arm, magnet, and brake shoes.
Make certain that all the parts removed are replaced in the same
brake and drum assembly. Inspect for any loose or worn parts,
stretched or deformed springs and replace as necessary.

!

CAUTION

POTENTIAL ASBESTOS DUST HAZARD!
Some older brake linings may contain asbestos dust,
which has been linked to serious or fatal illnesses.
Certain precautions need to be taken when servicing
brakes:
1. Avoid creating or breathing dust.
2. Avoid machining, filing or grinding the brake linings.
3. Do not use compressed air or dry brushing for
cleaning (dust can be removed with a damp brush).

Brake Lubrication
Before reassembling, apply a light film of grease or anti-seize
compound on the brake anchor pin, the actuating arm bushing
and pin, and the areas on the backing plate that are in contact
with the brake shoes and magnet lever arm. Apply a light film of
grease on the actuating block mounted on the actuating arm.

CAUTION
Do not get grease or oil on the brake linings, drums or
magnets.

-15-

Braking Systems - Electric

Brake Cleaning and Inspection

Magnets
Your electric brakes are equipped with high quality electromagnets
that are designed to provide the proper input force and friction
characteristics. Your magnets should be inspected and replaced if
worn unevenly or abnormally. As indicated below, a straightedge
should be used to check magnet condition. For best results, the
magnet should be flat.
Even if wear is normal as indicated by your straightedge, the
magnets should be replaced if any part of the magnet coil has
become visible through the friction material facing of the magnet.
It is also recommended that the drum armature surface be refaced
when replacing magnets (see section on Brake Drum Inspection).
Magnets should also be replaced in pairs - both sides of an axle.
Use only genuine Dexter replacement parts when replacing your
magnets.

Braking Systems - Electric

Straight Edge

Gaps show ABNORMAL
WEAR (replace magnet)

NORMAL WEAR

-16-

A simple visual inspection of your brake linings will tell if they
are usable. Replacement is necessary if the lining is worn to
¹⁄₁₆" or less. Shoes
contaminated with
grease or oil, or
abnormally scored
or gouged should
also be replaced.
Hairline heat cracks
are normal in bonded
linings and should not
be cause for concern.
When replacement
Acceptable Hairline Cracks
is necessary, it is
important to replace
both shoes on each brake and both brakes of the same axle. This
will help retain the “balance” of your brakes.

!

CAUTION

POTENTIAL ASBESTOS DUST HAZARD!
Some older brake linings may contain asbestos dust,
which has been linked to serious or fatal illnesses.
Certain precautions need to be taken when servicing
brakes:
1. Avoid creating or breathing dust.
2. Avoid machining, filing or grinding the brake linings.
3. Do not use compressed air or dry brushing for
cleaning (dust can be removed with a damp brush).
After replacement of brake shoes and linings, the brakes must
be re-burnished to seat in the new components. This should be
done by applying the brakes 20 to 30 times from an initial speed
of 40 m.p.h., slowing the vehicle to 20 m.p.h. Allow ample time for
brakes to cool between applications. This procedure allows the
brake shoes to seat in to the drum surface.

-17-

Braking Systems - Electric

Shoes and Linings

Introduction to Troubleshooting
Proper brake function is critical to the safe operation of any
vehicle. If problems are encountered with your trailer braking
system, the following guide can be used to find the causes and
remedies for some of the more common problems. If you are
unsure or unable to resolve the problem, please contact your
nearest repair facility for professional assistance.

Troubleshooting
Most electric brake malfunctions that cannot be corrected by either
brake adjustments or synchronization adjustments, can generally
be traced to electrical system failure. Voltmeters and ammeters
are essential tools for proper troubleshooting of electric brakes.
Mechanical causes are ordinarily obvious, i.e. bent or broken
parts, worn out linings or magnets, seized lever arms or shoes,
scored drums, loose parts, etc. Replace defective parts with
genuine Dexter replacements.

Braking Systems - Electric

Please consult the following troubleshooting charts to determine
the causes and solutions for common problems found in trailer
braking systems.

!

CAUTION

Best braking performance is achieved with a controller
setting that is just short of wheel lock up or slide. Overly
aggressive braking which results in wheel lock up and
sliding, can cause a dangerous loss of control and
result in personal injury or death.

-18-

SYMPTOM

No Brakes

CAUSES

REMEDIES

Open Circuits

Find & Correct

Severe
Underadjustment

Adjust Brakes

Faulty Controller

Test & Correct

Short Circuits

Find & Correct

Grease or Oil on
Magnets or Linings

Clean or Replace

Corroded Connections

Clean & Correct
Cause of Corrosion

Worn Linings
or Magnets

Replace

Scored or Grooved
Brake Drums

Machine or Replace

Improper
Synchronization

Correct

Underadjustment

Adjust Brakes

Glazed Linings

Reburnish or Replace

Overloaded Trailer

Correct

Underadjustment

Adjust

Improper
Synchronization

Correct

Faulty Controller

Test & Correct

Loose, Bent or Broken
Brake Components

Replace Components

Out-of-Round
Brake Drums

Machine or Replace

Insufficient Wheel Load

Adjust System Resistor
and Synchronize

Faulty Controller

Test & Correct

Broken Wires

Repair or Replace

Loose Connections

Find & Repair

Faulty Ground

Find & Repair

Weak Brakes

Locking Brakes

Intermittent Brakes

-19-

Braking Systems - Electric

Troubleshooting

Troubleshooting
SYMPTOM

Brakes Pull to
One Side

CAUSES

REMEDIES

Wrong Magnet
Lead Wire Color

Correct

Incorrect Adjustment

Adjust

Grease or Oil on
Linings or Magnets

Clean or Replace

Broken Wires

Find & Repair

Bad Connections

Find & Repair

Underadjustment

Adjust

Improper
Synchronization

Correct

Improper Controller

Change

Faulty Controller

Test & Correct

Harsh Brakes

Underadjustment

Adjust

Lack of Lubrication

Lubricate

Noisy Brake

Braking Systems - Electric

Broken
Brake Components

Surging Brakes

Dragging Brakes

Replace Component

Incorrect Brake
Components

Correct

Grease or Oil on
Linings or Magnet

Clean or Replace

Out-of-Round or
Cracked Brake Drums

Machine or Replace

Faulty Controller