INSTALLATION INSTRUCTIONS

Model 850E Actuator for Trailer Brakes
READ AND UNDERSTAND THE ENTIRE INSTRUCTION/ASSEMBLY
PROCEDURE BEFORE INSTALLING YOUR BRAKES AND ACTUATOR.

1&6
5

The Model 850 works by the “surge” or “push” of the trailer toward
the tow vehicle. This automatically synchronizes the trailer brakes with
the tow vehicle axle brakes. When the trailer pushes against the tow
vehicle, the actuator telescopes together and applies the force to the
master cylinder, supplying hydraulic pressure to the brakes. The built in
dampening shock absorber retards the telescoping shock against the
hitch ball. Low levels of brake fluid will signal the tow vehicle operator to
add brake fluid via coupler knocking.

1

7

3

5

Be sure to comply with regulations for brakes in your state. Brake laws
sometimes are minimum standards and you may wish to add additional
brakes to your trailer to meet minimum Gross Vehicle Weight Ratings
(GVWR).

5
4
1A

!

1

Brake laws sometimes are minimum standards and you may
wish to add additional brakes to your trailer. Read your tow
vehicles owner’s manual on towing capacity and other towing
recommendations before installing brakes or this actuator.

1

The Model 850 Actuator is completely assembled and ready to bolt into
place (Tongue sizes: 3”x3”, 3”x4” & 3”x5”).

2

#

TDE Part #

CAUTION

1.

Bolt the actuator to the tongue using 5/8” diameter, 4” long grade
5 bolts. Lightweight tongues, less than 10 gauge, require spacer
tubes inside the tongue for reinforcement. Attachment strength
should equal or exceed 1-1/2 times trailer G.V.W.R.

DX Part #

Description

1A

K68-531-00

Brake Master Cylinder Kit
Includes: master cylinder and cap, 4
mounting screws with washers, 2 rollers,
nuts and bolts

2.

70561K Disc

Hydraulic brake lines should be installed on the trailer as described
in the installation manual supplied with the brakes. Note: Some disc
brakes require the use of flexible brake lines at the connection POINT
on the brake caliper. Follow brake manufacturer instructions.

1B

11286

054-140-00

Disc Brake Solenoid

3.

Use only DOT-3 brake fluid in the Model 850 actuator. Use
a pressure type brake bleeder to bleed brakes, following
manufacturer’s instructions or manually bleed the brakes using
instructions on page 3.

4.

Check with your state motor vehicle department for laws
concerning minimum trailer brake requirements. Some states may
require brakes on all axles.

5.

Road test trailer a short distance to activate the actuator several
times. This will fill the reservoir of the master cylinders shock
dampening system. Check fluid level again. Remember, low brake
fluid levels will result in hitch ball knocking.

6.

When testing is completed, make sure master cylinder is filled to
approximately 3/8” below the top of the reservoir and filler cap is
securely in place. Road test again to make sure brakes work properly.

2

70411

068-562-00

Latch Kit Assembly, with Drop-N-Go™
Coupler, (serial numbers 17926 & below)

2

70412

068-563-00

Latch Kit Assembly, with Drop-N-Go™
Coupler, (serial numbers 17927 & above)

3

50317

068-738-10

Emergency Stop Cable (E-stop/
Breakaway)

4

50301

074-477-00

Safety Cable with stainless steel pin Includes mounting screw

5

70462K

K68-524-00

Actuator Covers, Includes: front and rear
cover plates and 4 mounting screws

6

48986A

068-572-00

Master Cylinder Fill Cap with internal
bladder, 2.25” Opening

7

48844

046-259-00

Safety Spring with two mounting screws

©2019 Dexter Axle Company | www.dexteraxle.com

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RATED CAPACITY: Maximum Actuator Capacity: 8500 lbs. Gross Load,
850 lbs. Maximum Tongue Load, 425 lbs minimum tongue load.

!

The actual in-service rating is limited to that of the ball and hitch being
used or the trailer manufacturer’s G.V.W.R. shown on the certification
label, whichever is lower (Note: GVWR is the Gross Vehicle Weight Rating
which includes the trailer and the load weight as a Total Gross Weight).

!

• A loose fit between the coupler and hitch ball can cause the
actuator and hitch ball to separate, causing serious damage,
injury or death. Check coupler every time prior to towing and at
each stop on long trips. Always make certain that coupler latch
safety pin is securely installed into coupler latch.

CAUTION

• A minimum of 5% tongue weight and a maximum 10% tongue
weight of the trailer GVWR must be located on the hitch ball. The
Trailer tongue should be parallel to the ground. Too much weight
can cause premature brake actuation and loss of control of the
towing vehicle. To little tongue weight can cause the trailer to
fishtail, resulting in loss of control of the tow vehicle and trailer
(total trailer weight GVWR includes weight of the trailer plus load).

AVOID sharp turns, which can cause the actuator to bind
or jackknife against the tow vehicle or cause a bend in the
tongue. Either can damage the actuator causing brake failure.
AVOID towing trailer across large bumps or dips that may over
stress the connection between the trailer and tow vehicle, as
this could result in damage to the actuator.

• Never allow the coupler latch safety pin to remain in the reverse
lockout position hole. After reverse maneuvering, always insert
coupler latch safety pin back into coupler latch. FAILURE TO
REMOVE SAFETY PIN FROM REVERSE LOCK OUT POSITION HOLE
WILL PREVENT FORWARD MOVEMENT BREAKING THAT CAN
RESULT IN SERIOUS PROPERTY DAMAGE, INJURY OR DEATH.

HITCHING TRAILER
1.

The vehicle, towing hitch and ball must have a rating equal to or
greater than trailer GVWR.

2.

Model 850 will accept 2” trailer hitch balls with a 8500 capacity.
Trailer balls larger than 2.00” or out of round will not fit the coupler
or may result in coupler failure. Balls smaller than 1.97” can cause
shock loading and sudden disconnection. Make certain ball latch
is in correct position to retain the hitch ball. Push latch lever back
until safety latch engages plate below lever latch. Always insert
safety pin into forward hole as a safety lock for the hitch ball
coupler prior to towing. Do not tow trailer if coupler is damaged.

3.

Connect safety cables or chains using crossed pattern under
tongue, or follow trailer manufacturer’s directions.

4.

Connect actuator breakaway cable S-hook to the tow vehicle only.
Do not connect S-hook to the safety cables or chains.

5.

The breakaway system is designed to only operate after the trailer
detaches from the tow vehicle and the safety cable/chains have
failed. The breakaway is not a parking brake. Do not use as such.

!

8.

9.

©2019 Dexter Axle Company | www.dexteraxle.com

CAUTION

Failure to install the hitch pin before towing can result in
accidental opening of the coupler hitch latch, which can lead to
the trailer coming off of the hitch ball, causing serious damage,
injury or death. If pin will not fit into the front lower hole, the
coupler is not attached properly. Reset coupler on hitch ball.

• When resetting the breakaway system, keep hands and fingers
clear as you reset the mechanism. Hydraulic pressure held in the
system may cause the assembly to snap back suddenly.

Any control devices that restrict operation of the actuator cannot
be used. This includes certain sway control devices. The actuator
must be free to telescope in response to braking requirements.

The actuator is designed for use with Free-Backing trailer brakes.
To block braking action, (in order to back up) with other types of
brakes, use an electric solenoid. For reverse trailer movement when
braking is not required, place the safety pin in the upper hole
on the side of the actuator to block movement of the actuator.
DANGER: Failure to remove pin will also prevent forward braking.
Pin must be in the lower, forward coupler hole as a safety lock for
the hitch ball coupler latch when towing at all times.

!

• In the event that the breakaway system is used, check all system
components (cable, S-hooks, etc.) for proper working order.
Replace any damaged parts with genuine Dexter parts only.

7.

CAUTION

Tongue weight beyond rating limits will interfere with performance
of actuator, braking system and the tow vehicle.

• The breakaway system is not designed to operate if the trailer does
not separate completely from the tow vehicle, or if the tongue goes
under the rear of the tow vehicle.

If the breakaway is accidentally applied while un-hitching, insert a
flat bladed screwdriver into the spring clip slotted hole under the
actuator and pry down to release.

Equalizing or weight distributing hitches may be used, allow six to
eight inches free chain length.

!

CAUTION

6.

CAUTION

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MAINTENANCE

!

3.

The screwdriver should be at the lowest angle possible to the
actuator so that it slides in front of the e-stop bracket (1B).

4.

Screwdriver tip MUST BE IN FRONT of the e-stop bracket and NOT
in the slot on the e-stop bracket (2A).

5.

Push the screwdriver forward and back to pump the master
cylinder. (2B).

CAUTION

The exterior of the actuator and brakes should always be rinsed with
fresh water after use in corrosive conditions. Before storing trailer,
clean brakes and repack the bearings. Failure to properly maintain
the actuator could cause serious damage, injury or death.
1.

Always check the brake fluid reservoir before using trailer. Make
sure it is at least half full. If not, refill to approx. 3/8” below the top
of the reservoir with DOT 3 brake fluid. Check for leaks and repair
as required. Never reuse brake fluid.

!

CAUTION

DO NOT REUSE BRAKE FLUID. Always use fresh DOT 3 fluid from
a fresh container. Failure to maintain proper levels of fluid in the
reservoir will cause brake failure.
2.

The model 850E is equipped with two “Super Lube” pins to provide
grease to the inner rollers. Use a grease gun to lubricate the rollers
through the grease fittings provided, every 6 months. For heavy
use, grease every 3 months.

3.

To extend coupler and ball life, coat both with a thin coating of
grease. This will also eliminate squeaking. Wipe clean and renew
grease film each time trailer is used.

4.

Examine the actuator for bent parts or wear each time the trailer is
used. Replace parts as necessary. There are no user adjustments
on the actuator.

5.

Actuator travel (shown by coupler roller path) over 1” indicates
adjusting the brakes, adding fluid to the reservoir or a needing
to bleed the brakes and check connections for leaks. Adjust per
instructions found in brake installation manual. In general, back-off
the adjusters on drum brakes from locked position, as required.
Adjust Free-Backing brakes by rotating Bleeding
wheel in forward direction only. Failure to Access Port
adjust may result in loss of braking. Disc
brakes do not require adjustment, check
for pad wear periodically.

1B
2B

7.

When bleeding and testing is completed, make sure master
cylinder is filled to ³⁄₈” below the top of the reservoir and filler cap
is securely in place.

Release emergency stop cable by prying spring out with a flat blade
screw driver.
FRONT
Normal operating position
If button stop cable is showing
DO NOT TOW TRAILER

While towing, if the actuator appears to
be knocking against the hitch ball while
starting or stopping, check brake fluid
reservoir and fill if below 3/8” full from the top. Dampening shock
absorber requires sufficient brake fluid in order to retard movement
of coupler against hitch ball during towing.

Bleeding Instructions
FRONT

The bleeding operation for that brake is complete when bubbling
stops. Be sure to tighten bleeder screw securely. Each wheel
cylinder must be bleed until all air is out of the lines. Replenish the
brake fluid during the bleeding process so the level does not fall
below half full level in the master cylinder reservoir.

Emergency Button Stop

FRONT

6.

6.

FRONT

1.

To bleed master cylinder and brakes, install bleeder hose on first
wheel cylinder to be bled; if tandem axle trailer, bleed farthest
axle first, and the farthest brake on that axle first. Use a loose end
of hose from the bleeder valve submerged in a clear container of
brake fluid to observe bubbling (hose must be submerged into
clean brake fluid to keep air from traveling back into the brake
cylinder). .

2.

Pump master cylinder, keeping pressure, using a flat tip screwdriver
(1A). Crack bleeder value open and tighten. Repeat until there are no
more air bubbles.

©2019 Dexter Axle Company | www.dexteraxle.com

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059-Z00-47 2019.10 | 08163-2