INSTALLATION AND SERVICE INSTRUCTIONS
DX20EX Actuator

air bubbles can be observed. Open the bleeder screw one turn.
Pull the breakaway lever completely forward or vertical and close
the bleeder screw to prevent air from being pulled back into the
system. Air trapped in the brake lines will greatly reduce your braking
efficiency. Push the breakaway lever down to nearly flat position.
Repeat this process until no more air bubbles are released with each
stroke. Be sure to close the bleeder screw securely.

CAUTION

DO NOT submerge actuator. To minimize the damaging effects of
corrosion on a braking system used under corrosive conditions,
actuator should be externally flushed after use with a high pressure
water hose. Lubricate all moving parts after the unit has dried.
Failure to properly and adequately clean, grease, and maintain the
actuator can cause failure and result in serious injury.

6.

This actuator arrives completely assembled and ready to install. Only
paint a disassembled outer member. Do not paint other components of
the actuator, as this can cause failure.
RATED CAPACITY AND TONGUE LOADS VARY. PLEASE REFERENCE THE
COUPLER CASTING AND TOP PLATE OF ACTUATOR FOR CAPACITIES.
When used with disc brakes or non free-backing brakes, a solenoid
backup valve will allow the trailer to be backed without activating the
brakes. Do not block actuator movement in and out to back up the trailer.
Failure to remove the blocking device will prevent all trailer braking.
1.

2.

Repeat the bleeding operation at each wheel cylinder or caliper.
During the bleeding process, replenish the brake fluid so the level
does not fall below half full level in the master cylinder reservoir. When
bleeding is complete, fill the reservoir to within 3/8” of the top. Install
the filler cap securely. To reset the breakaway lever, loosen the front
two bolts. Position the breakaway lever and rotate the two breakaway
locks to their original operating or ready position. Install the two rear
bolts and lock washers and torque all four bolts to 90-120 ft.-lbs.

System Test
This procedure only indicates if the trailer brake system is functional.
Regular inspection, maintenance, and adjustments of all brake system
components are still required to ensure brake operation and performance.

Welding is the perfected mounting option. If not welding, bolt the
actuator to the tongue using grade 5 or better mounting hardware.
Light weight tongues require spacer tubes inside for reinforcement
when bolting. Tighten mounting bolts to 80 ft.-lbs.
Install brakes and brake lines per manufacturers instructions. DO
NOT remove or modify the orifice connector at the rear of your
actuator’s master cylinder. It connects directly to the brake tubing
and ensures proper fluid flow characteristics. FLEXIBLE BRAKE
LINE HOSE MUST BE USED to connect the orifice connector at
the master cylinder to the hydraulic brake line on the trailer. This is
necessary because the master cylinder is spring mounted to provide
overload protection and thus moves relative to the outer member.

1.

Move the trailer to flat, level ground, pulling FORWARD several feet
before parking. This forward motion will ensure trailers equipped
with free-backing brakes are in their normal operating mode. Chock
wheels, allowing for small testing motion. Disconnect the trailer
from tow vehicle and jack the trailer’s tongue until it is horizontal.3

2.

Hook the trailer’s safety chains (NOT the actuator’s breakaway
cable/chain) together to form a loop, which is centered below the
actuator’s coupler.

3.

Place a sturdy board, into the chain loop below the coupler. The board
should be 4 feet or longer so it will extend several feet above the
actuator. Keep the end of the board a few inches off the ground, and
position it to press against the front end of the actuator’s coupler.

4.

Stand in front of the trailer and face the rear. Apply force to the top
end of the board to use it as a lever. Press back towards the rear of
the trailer. The board will begin moving the inner member into the
actuator’s outer member.

5.

Keep pressing the top of the board to stroke the actuator and its
internal master cylinder. If the trailer brake system is operational, the
brakes will apply and keep the trailer from rolling away from you. Disc
brakes and properly adjusted uni-servo or duo-servo type brakes will
prevent you from moving the trailer back more than a few inches.

CAUTION

Incorrectly filling or bleed the brakes can result in brake failure.
Only use fresh brake fluid from sealed container. DO NOT reuse
fluid. After filling and bleeding, remember to refill the actuator.
Failure to maintain an adequate fluid level may cause failure.
3.

Fill and bleed the brake system per manufacturer’s instructions.

4.

Fill master cylinder to 3/4 full with DOT-3 brake fluid. DO NOT allow
brake fluid to contact painted surfaces since it will damage the
finish. Wipe up any spills immediately and wash the area with water.

5.

When the air bubbling stops inside the master cylinder, install a
bleeder hose on the bleeder screw of the first wheel cylinder or disc
brake caliper to be bled. Be sure to use the bleeder screw on top of
the caliper. Start with the rear axle on tandem axle trailers. Submerge
the other end of the hose in a glass container of brake fluid so that

©2022 Dexter Axle Company | www.dexteraxle.com

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059-A60-03 | 2022.10

Free-backing type brakes will initially provide rolling resistance, but
continued force on the board will switch them into free-backing
mode, and you’ll be able to move the trailer backwards.

or other damage. Have the affected components replaced with
genuine Dexter service parts. Check to determine that the actuator
mounting bolts are torqued to 80 ft.-lbs.
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Test the actuator and brake function as previously described.
Actuator travel over 1” indicates that the brakes need adjustment.
Adjust the brakes according to manufacture instructions if needed.
There are no adjustments on the actuator.

Hitching Trailer

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Attach the actuator’s breakaway chain S-hook securely to one of the tow
vehicle hitch safety chain connection points. Confirm that the trailer’s
safety chains are adjusted relative to the actuator’s breakaway chain as
noted above. DO NOT loop the breakaway chain around a bracket and
hook it back onto itself.

A film of grease on the hitch ball will extend coupler and ball life
while eliminating squeaking. Wipe clean and renew film each time
trailer is used.

ƒ

Before storage or after extended use, apply motor oil to the coupler
components, lockout mechanism, and the three internal rollers to
keep them moving freely and to prevent corrosion.

6.

If stroking the actuator causes the trailer to roll away from you
freely or with only minimal resistance, the brakes are NOT applying
properly. Evaluate the brake system to determine cause. Corrective
action MUST be taken before the trailer is used.

DX20EX Assembly
Over time, you may need to disassemble your actuator for service or to
replace components.

CAUTION

Safety chains must be used. The length MUST be set short enough
so the actuator’s breakaway cable is NOT pulled if the coupler
separates from the tow vehicle’s hitch but remains connected by
the safety chains.

1.

Place the centering plate on the inner member and secure in place
with two 5/16” bolts and lock washers.

2.

Position the small diameter end of the damper to line up with the
lower holes in the front of the inner member. Install damper pin
and secure it with a cotter pin. Repeat the process with the second
damper in the upper holes of the inner.

3.

Insert a spacer tube into the edge of the top slot. Then slide the spacer
tube through a rear roller with the chamfered edge out, then through
the end of the damper, and finally through another rear roller with the
chamfered edge out. Repeat the process for the bottom damper. Insert
the third spacer tube into the back part of the long top slot.

4.

Install the rear roller with chamfered edge out, a spacer, and the
rear roller with the chamfered edge out. Carefully insert the inner
member into the outer member maintaining the position of the
components on the spacer tubes. Install a rear roller bolt into the
front top spacer tube and start the castle nut on the bolt. Repeat
the process for the bottom spacer tube.

5.

Insert the final top bolt through the remaining spacer tube and
start the castle nut. Run the castle nuts down lightly against the
outer member and secure with cotter pins.

6.

Take two front rollers and place in position in the front roller cover.
Line up the holes in the roller cover and the outer member and thread
the front roller bolt through the outer member, front roller cover, and
the front roller. Secure the bolt with the lock washer and the nut.
Repeat the process with the other roller bolt. Tighten nuts to 75 ft.-lbs.

7.

Place the breakaway lever assembly in the rectangular opening
in the top of the outer member. Install the weather seal with the
slot forward on top of the brackets. Position the right and left
breakaway locks and start the four 5/16” bolts with lock washers.
Move the breakaway lever to vertical position and use a locking
pliers to hold the breakaway locks close to the lever to assure the
tabs will hold the lever in position. Torque bolts to 90 – 120 ft.-lbs.
Spread the top of the breakaway locks to allow the breakaway lever
to move down to normal operating position (about 45 degrees).

8.

Remove the filler cap from the master cylinder and slide the
assembly into the back of the outer member. Line up the front
holes first and start two 5/16” bolts and lock washers. Repeat the
process for remaining bolts and tighten all bolts. Then thread the
filler cap in the master cylinder and install the cylinder cover.

Resetting the Breakaway Lever
The pressure in the system may cause the lever to snap back quickly.
Keep hands and fingers clear as you reset the breakaway mechanism.

CAUTION
DO NOT use breakaway systems as a parking brake.
1.

Carefully loosen the brake line fitting going into the actuator. After
the pressure is gradually released, re-tighten the fitting.

2.

Remove the two rearward bolts, one located on each side of the
breakaway lever. These two bolts hold down the breakaway locks.
Loosen, but do not remove the two remaining bolts. This will allow
the two locks to be swung aside and the lever can be pushed back
into its resting position. Rotate the breakaway locks to their original
positions and torque the four bolts to 90-120 ft.-lbs.

3.

Before towing, check that the breakaway lever and chain are
properly positioned.

CAUTION
An incorrect lever or chain position may cause the trailer
brakes to drag and overheat, or may keep the brakes from
being applied in a breakaway situation. After any usage of the
breakaway mechanism, either real or accidental, check all
system components for damage. Replace any damaged items with
genuine Dexter service parts.

Pre-Towing Check List
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Check that the brake fluid reservoir is 3/4- full of DOT 3 brake
fluid. Check for leaks and repair as required.

CAUTION

Use only fresh brake fluid from sealed container. DO NOT reuse fluid.
Failure to maintain an adequate fluid level may cause brake failure.
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Examine the actuator for wear, bent parts, corroded/seized parts,

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059-A60-03 | 2022.10