STOWAWAY Tailgates By THIEMAN

ST 22 & ST 31
OWNERS MANUAL/PARTS LIST

ST 31 SHOWN

! IMPORTANT! KEEP IN VEHICLE!

PLEASE READ AND UNDERSTAND THE CONTENTS OF THIS
MANUAL BEFORE OPERATING THE EQUIPMENT.

HIEMAN
TAILGATES, INC.
NATIONAL TRUCK EQUIPMENT ASSOCIATION 600 East Wayne Street
Member
Celina, Ohio 45822
Phone: 419-586-7727 Fax: 419-586-9724
 TABLE OF CONTENTS
PARTS ORDERING PROCEDURE ....................................................2
WARNINGS.........................................................................................3
OPERATING INSTRUCTIONS............................................................4
MAINTENANCE GUIDE ......................................................................4
SEMI-ANNUAL INSPECTION .............................................................5
ELECTRICAL PICTORIALS ................................................................6
INSPECTION AND LOCATION OF DECALS......................................7
PLATFORM .........................................................................................8
SPACER ASSEMBLY ..........................................................................9
TRUNNION, LIFT ARM, AND IDLER ARM ASM-ST22 .....................10
TRUNNION, LIFT ARM, AND IDLER ARM ASM-ST31 .....................11
ELECTRIC CONTROL PUMP ASM POWER DOWN-ST22 .............12
ELECTRIC CONTROL PUMP ASM GRAVITY DOWN-ST22............13
ELECTRIC CONTROL PUMP ASM POWER DOWN-ST31 .............14
ELECTRIC CONTROL PUMP ASM GRAVITY DOWN-ST31............15
TROUBLESHOOTING GUIDE.....................................................16-18

FOR YOUR RECORDS

Model No. __________________________ Date Purchased _______________________

Serial No._________________________________________________________________
NOTE: When Ordering Parts Be Sure To Include This Information!

PARTS ORDERING PROCEDURE

When ordering parts, please include all the information asked for below. If this information is
not available, a complete written description or sketch of the required part will help Thieman
identify and deliver the needed part to you.

THE FOLLOWING INFORMATION MUST BE INCLUDED:

1. Serial Number – Thieman liftgate serial numbers can be found on the tag located on
the front side of the trunnion tube.
2. Model Number and Capacity.
3. Platform size and Material – Steel or Aluminum.
4. Part number.
5. Description.
6. Quantity required.
 WATER LEVEL LOADING
When a maximum load is to be raised or lowered, this load must be centered on the
load bearing platform, both front to back and side to side.

WARNING!

The following list of warnings are to be read before operating the ST series liftgate.

+ Read this Owners Manual and all of the decals on the liftgate BEFORE operating the
liftgate.
+ All protective covers and guards must be in place before operating the liftgate.
+ DO NOT operate the liftgate if you do not have a thorough knowledge and understanding of
the operation of the liftgate.
+ NEVER OVERLOAD THE LIFTGATE. The maximum rated capacity of the ST series liftgate
differs with each model as follows:
ST22 – 2200LBS
ST31 – 3100LBS
+ Never use the liftgate if it makes any unusual noises, has vibrations, or fails to operate
freely.
+ Make certain that the area below the platform is clear before and at all times during the
operation of the liftgate.
+ Keep hands and feet clear of all pinch points.
+ The platform must in the closed position and the transit chains attached properly before
transit.
+ Always load as close to the center of the platform and as close to the vehicle as possible.
See figure 1.
+ Never operate lift trucks on or over any part of the platform.

3.
+ Load and unload the platform from the rear and not from the side of the platform.
+ Only operate liftgate when vehicle is on level ground and the parking brake is set.
+ Follow the maintenance guide as outlined in this manual.
+ DO NOT attempt any repairs unless you are qualified to do so.
+ If any repairs, adjustments, or maintenance not covered in this manual are required, con-
tact your nearest Thieman distributor or the factory.

OPERATING INSTRUCTIONS
Caution
Be sure to operate liftgate at a safe distance and never improperly load platform as this may
cause personal injury or damage to the liftgate.

UNFOLDING OF PLATFORM
1. Lower platform to ground until lift arms contact the ground.
2. Grasp platform handle on bottom side and manually unfold the platform to the ground. The
platform extension can now be unfolded to the ground.

RAISING OF PLATFORM
3. Push toggle switch up to raise platform to bed height.

LOWERING OF PLATFORM
4. Push toggle switch down to lower platform to the ground.

CLOSING OF PLATFORM
5. Manually fold platform extension and ramp.
6. Using platform handle, manually fold platform.
7. Raise gate into the stowed position until latches are engaged over pins.

THERMAL DATA: To avoid overheating the motor do not operate this unit for more than 8
cycles/10 minutes with the maximum load. The motor then must be allowed to completely cool
down to ambient temperature before cycling the lift again. This unit also has a 15% duty cycle,
which means the liftgate can be cycled no more than 3 cycles/10 minutes constantly with a
maximum load.

MAINTENANCE GUIDE
The following inspection and maintenance operations should be performed at the recommended
intervals or anytime the liftgate shows signs of abuse, and improper or abnormal operation.

MONTHLY INSPECTION AND MAINTENANCE

Operate the liftgate throughout its entire operational cycle and check the following:
1. Check that there are no unusual noises or vibrations.
2. Check platform height relative to bed height. If platform is lower, adjust cylinder with a
13/16 wrench to obtain the necessary height.
3. Check for apparent damage to the liftgate such as bent or distorted members, any cracked
welds which may have resulted from overloading or abuse.
4. Check for excessive wear in the following areas:
A. Platform hinge pins and lift arms
B. All cylinder pins, bolts, and clevis
C. Platform extension pivots
D. Linkage pins and clevises
5. Check that the platform pivot pins are in place and retained by their proper retainers.
6. Check that all protective covers and guards are properly in place and secured.
7. Check for oil leaks in these areas:
A. Lift cylinder
B. Hydraulic hose-replace if it shows signs of wear or cracking.

4.
 C. Hydraulic fittings-tighten or replace as may be required to stop leakage.

8. Check the oil level in the pump reservoir. With the liftgate in the stowed position the oil
should be within 1/2” from the top of the reservoir. See chart below for oil applications.
9. Check that all wiring and battery cable connections are tight and free of corrosion.
10. Lubrication of the ST series liftgate should be as follows:

Area of Tailgate Type of Lubrication Frequency

Pivot pins w/ zerk Grease* 50 cycles
Pump oil change see chart below yearly
Control handle pivots SAE 10 or 20 oil 50 cycles
*See the parts list for location of the grease zerks.
For -40 to 120 F use #0 Grade grease.
For -20 to 200 F use #1 Grade grease.

HYDRAULIC FLUID CHART

Temperature Range Acceptable Fluids

-75 to 165oF Exxon Univis J-26

-20 to 130oF Dexron III

Exxon Superflo ATF
Shell Donax TG

-50 to 80°F Shell Aero Fluid 4

Mobil Aero HFA
Exxon Univis J-13
MIL H-5606
11. Check the pump relief pressure and also the motor amperage at this pressure. These values
should be as follows:
Model Max Amp Draw Relief Pressure (psi)
ST 22 175 2200
ST 31 175 2200
Semi-Annual Inspection
1. Perform the procedures outlined in the Monthly Inspection and Maintenance.
2. Inspect pump motor by:
A. Disconnecting battery cable
B. Remove motor end cover
C. Examine the armature brushes for wear. (Brushes should be replaced if they are less
than 1/8” long).
D. Clean all residue out from inside of the motor housing.
E. Apply several drops of light weight machine oil to the armature shaft bearing in the
motor end cover and reassemble the motor end cover.
3. If the hydraulic oil in the reservoir is dirty:
A. Unfold platform and lower platform to the ground. Raise platform to bed height so
cylinders are fully retracted. Support the platform in this position with a lift truck or
crane.
B. Drain the oil from the hydraulic system and flush the entire system.
C. Remove reservoir from pump and clean suction line filter. Also clean out any
contaminants inside reservoir. Remount reservoir when completed.
D. Replace the oil as outlined in Section 9 under Monthly Maintenance and Inspection.

5.
ELECTRICAL PICTORIAL

6.
 INSPECTION AND LOCATION OF DECALS
Inspect all of the decals listed below to be certain that they are in the proper location and
they are legible. All decals must be in place and legible or all warranties are void!

Item Part Name Part Number

1 Warning Decal-off center 4671050
2 Fast Idle Decal 4650150
2 PTO Decal 4650140
3 Danger Decal-no riding 4609
4 Operating Decal-Toggle 4606
5 Capacity Decal-2200# 4650540
5 Capacity Decal-3100# 4650740
6 Warning Decal-pinch point 4604
7 Handle decal 4605
8 Thieman Nameplate 4650800
9 Urgent Warning Decal 4650530
10 Wiring Decal - Gravity Down 4612
10 Wiring Decal - Power Down 4614
11 Warning Decal 4620

7.
 PLATFORM ASSEMBLY

Item Part Number Description List Price Qty.

1 31324 Platform Main Section $918.40 1

2 31124-001 Platform Extension $470.78 1
3 5781017 Retaining Ring $1.12 4
4 5056 Hinge Pin $7.17 2
5 8271856 Screw 1.00 x 2.25 $5.60 2
6 8426899 Nut 1.00 $1.12 2
7 8271291 Zerk $0.56 2
8 31325 Platform Asm 8440 $1,384.32 1
9 8107-011 Washer .62 $0.56 2

8.
 SPACER ASSEMBLY

Item Part Number Description List Price Qty

1 3195 Spacer Asm $784.00 1

2 2404-001 Control Shaft $60.48 1
3 5701043 Handle Grip $2.24 1
4 3192-002 Latch RH $32.39 1
5 3192-001 Latch LH $32.39 1
6 5101100 Spring $2.15 2

9.
 TRUNNION, LIFT ARMS, AND IDLER ARMS-ST22

Item Part Number Description List Price Qty

1 3103460 Trunnion Asm $742.29 1

2 3103590 Lift Arm Asm $514.82 1
3 31119-002 Idler Arm RH $220.46 1
4 31119-001 Idler Arm LH $220.46 1
5 3103480 Kicker Arm Asm $101.70 1
6 4100-013 Chain $24.12 1
7 5064 Pin Asm IA to pivot $21.28 2
8 5028 Pin IA, LA-trunnion $22.47 4
9 5000161 Pin Asm LA to pivot $19.22 2
10 5100180 Spring $8.96 1
11 8137243 Cotter Pin $0.56 1
12 8427570 Screw .44 x 2.50 $1.12 2
13 8120396 Flatwasher .44 $0.34 2
14 8137185 Cotter Pin $1.12 2
15 9414073 Lock Nut .44 $0.34 2
16 5781009 Retaining Ring $0.90 10
17 8271291 Zerk $0.56 12
18 5708-001 Spring Pin $1.12 4
19 3103530 Hinge Asm CS $71.88 1
20 3103710 Spring Lever CS $69.91 1
21 8120384 Lockwasher .50 $0.34 1
22 8100-014 Screw .50 x 1.00 $1.12 1
23 5100050 Torsion Bar $117.56 1
24 5794001 Clevis Pin $3.58 2
25 2331150 Link $5.78 2
26 5708-005 Spring Asm $69.91 1
27 3103540 Hinge Asm SS $71.88 1
28 5702242 Wear Pad $15.41 2
29 8449646 Screws $0.56 4

10.
 TRUNNION, LIFT ARMS, AND IDLER ARMS-ST31

Item Part Number Description List Price Qty

1 3109400 Trunnion Asm $742.29 1
2 3109410 Lift Arm Asm $664.56 1
3 31119-002 Idler Arm RH $220.46 1
4 31119-001 Idler Arm LH $220.46 1
5 3103480 Kicker Arm Asm $101.70 1
6 4101-013 Chain $24.12 1
7 5064 Pin Asm IA to pivot $21.28 2
8 5028 Pin IA, LA-trunnion $22.47 4
9 5000161 Pin Asm LA to pivot $19.22 2
10 5100180 Spring $8.96 1
11 8137243 Cotter Pin $0.56 1
12 8427570 Screw .44 x 2.50 $1.12 2
13 8120396 Flatwasher .44 $0.34 2
14 5708-001 Spring Pin $1.12 4
15 9414073 Lock Nut .44 $0.34 2
16 5781009 Retaining Ring $0.90 8
17 3103530 Hinge Asm CS $71.88 1
18 3103710 Spring Lever CS $69.91 1
19 8120384 Lockwasher .50 $0.34 1
20 8100-014 Screw .50 x 1.00 $1.12 1
21 5100050 Torsion Bar $117.56 1
22 3103700 Spring Lever SS $69.91 1
23 3103540 Hinge Asm SS $71.88 1
24 2331150 Spring Link $5.78 2
25 5794001 Clevis Pin $3.58 2
26 5708-005 Spring Pin $1.12 2
27 8271291 Zerk $0.56 8
28 5702242 Wear Pad $15.41 2
29 8449646 Screw $0.56 4

11.
 ELECTRIC CONTROL PUMP ASSEMBLY POWER DOWN-ST22

Item Part Number Description List Price Qty

1 4404 EST Pump Asm-incl 2 to 5 $1,164.80 1

2 4421420 Pump bracket $66.68 1
3 4423520 Motor 8111 $311.96 1
4 4468 Solenoid $58.24 1
5 4420409 Breather cap $6.27 1
6 4318-001 Battery Cable #2 x 2' $20.94 1
7 5704 Cover $21.84 1
8 5700100 Strap $1.34 1
9 4930-001 Elbow MJ-MAORB $6.72 3
10 4951-015 Hose 51.00 $52.53 1
11 4931-001 Restrictor Elbow MJ-MAORB $14.11 1
12 4301770 Circuit Breaker $80.64 1
13 5001841 Pin Asm $8.71 2
14 42000 Cylinder 3.5 x 10 $517.44 1
15 4300030 Battery Cable #2 x 25’ $85.95 1
16 4350 Cable lug $4.84 1
17 5701260 Cable retainer $0.56 12
18 8180122 Screw .38-16 x 1.00 $0.56 5
19 8106-010 Internal Tooth Lockwasher .38 $0.34 10
20 8120377 Nut .38 $0.34 5
21 8120388 Flatwasher .38 $0.34 4
22 31445 Toggle Switch Asm $89.60 1
23 4319-002 Heat Shrink $1.68 1
24 4422860 Pushbutton Control $168.00 1
25 8111-005 Screw #10 x .75 $0.56 2
26 4318-002 Ground Cable #2 x 2' $16.24 1
27 8104-006 Screw .31 x 1 $0.56 1
28 4951-016 Hose 63.00 $57.01 1

12.
 ELECTRIC CONTROL PUMP ASSEMBLY GRAVITY DOWN-ST22

Item Part Number Description List Price Qty

1 4400351 Pump Asm-incl 2 to 6 $822.08 1

2 4421420 Pump bracket $66.68 1
3 4421350 Mounting bracket $9.65 1
4 4423520 Motor 8111 $311.96 1
5 4468 Solenoid $58.24 1
6 4420410 Breather cap $6.27 1
7 5704 Cover $21.84 1
8 5700100 Strap $1.34 1
9 4930-001 Elbow MJ-MAORB $6.72 1
10 4951-004 Hose 48.00 $51.18 1
11 4931-004 Restrictor Elbow MJ-MAORB $14.11 1
12 4301770 Circuit Breaker $80.64 1
13 5001841 Pin Asm $8.71 2
14 42000 Cylinder 3.5 x 10 $517.44 1
15 4300030 Battery cable #2 x 25’ $85.95 1
16 4350 Cable lug $4.84 1
17 5701260 Cable retainer $0.56 4
18 8180122 Screw .38-16 x 1.00 $0.56 5
19 8106-010 Internal Tooth Lockwasher .38 $0.34 10
20 8120377 Nut .38 $0.34 5
21 8120388 Flatwasher .38 $0.34 4
22 4933-001 Elbow BT-MAORB $13.44 2
23 4921-012 Tubing 42” $2.24 1
24 31446 Toggle Switch Asm $78.40 1
25 4318-001 Battery Cable #2 x 2' $20.94 1
26 4422850 Pushbutton Control $145.60 1
27 8111-005 Screw #10 x .75 $0.56 2
28 8104-006 Screw .31 x 1 $0.56 1
29 4318-002 Ground Cable #2 x 2' $16.24 1
30 4319-002 Heat Shrink $1.68 1

13.
 ELECTRIC CONTROL PUMP ASSEMBLY POWER DOWN-ST31

Item Part Number Description List Price Qty

1 4400911 EST Pump Asm-incl 2 to 6 $1,164.80 1

1 4400371 ESPB Pump Asm-incl 2 to 6 ??????? 1
2 4421420 Pump bracket $66.68 1
3 4948-004 Flow Control $70.90 2
4 4423520 Motor 8111 $311.96 1
5 4468 Solenoid $58.24 1
6 4420409 Breather cap $6.27 1
7 5704 Cover $21.84 1
8 5700100 Strap $1.34 1
9 4930-001 Elbow MJ-MAORB $6.72 2
10 4951-015 Hose 51.00 $52.53 3
11 4941-001 Straight Adapter MJ-MORB $1.90 2
12 4936-001 Elbow MAORB-MAORB $5.38 2
13 5001841 Pin Asm $8.71 4
14 4295 Cylinder 3 x 10 $398.72 2
15 4200481 Battery Cable #2 x 25’ $85.95 1
16 4350 Cable lug $4.84 1
17 5701260 Cable retainer $0.56 4
18 8180126 Screw .38-16 x 1.50 $0.56 5
19 8106-010 Internal Tooth Lockwasher .38 $0.34 10
20 8120377 Nut .38 $0.34 5
21 8120388 Flatwasher .38 $0.34 4
22 8104-006 Screw .31 x 1 $0.56 1
23 31445 Toggle Switch Asm $89.60 1
24 4422860 Pushbutton Control $168.00 1
25 4951-016 Hose 63.00 $57.01 1
26 4932-001 Branch Tee MJ-MJ-MAORB $10.42 1
27 8111-005 Screw #10 x .75 $0.56 2
28 4938-001 45° Elbow MAORB-FJS $38.98 1
29 31446 Branch Tee MJ-MJ-MJ $8.06 1
30 4319-002 Heat Shrink $1.68 1
31 4318-001 Battery Cable #2 x 2' $20.94 1
32 4301770 Circuit Breaker $80.64 1
33 4318-002 Ground Cable #2 x 2' $16.24 1

14.
 ELECTRIC CONTROL PUMP ASSEMBLY GRAVITY DOWN-ST31

Item Part Number Description List Price Qty

1 4400351 Pump Asm-incl 2 to 6 $822.08 1
2 4421420 Pump bracket $66.68 1
3 4421350 Mounting bracket $9.65 1
4 4423520 Motor 8111 $311.96 1
5 4468 Solenoid $58.24 1
6 4420410 Breather cap $6.27 1
7 5704 Cover $21.84 1
8 5700100 Strap $1.34 1
9 4953-001 Tee MJ-MJ-MJ $8.06 1
10 4951-004 Hose 48.00 $51.18 2
11 4931-001 Restrictor Elbow MJ-MAORB $14.11 2
12 4933-001 Elbow BT-MAORB $13.44 2
13 5001841 Pin Asm $8.71 4
14 4295 Cylinder 3 x 10 $398.72 2
15 4300030 Battery cable #2 x 25’ $85.95 1
16 4350 Cable lug $4.84 1
17 5701260 Cable retainer $0.56 4
18 8180126 Screw .38-16 x 1.50 $0.56 5
19 8106-010 Internal Tooth Lockwasher .38 $0.34 10
20 8120377 Nut .38 $0.34 5
21 8120388 Flatwasher .38 $0.34 4
22 4934-001 Tee BT-BT-MAORB $28.22 1
23 4921-012 Tubing 42.00 $2.24 2
24 4938-001 Swivel Elbow MAORB-FJS 45° $38.98 1
25 31446 Toggle Switch Asm $78.40 1
26 4422850 Pushbutton Control $145.60 1
27 8111-005 Screw #10 x .75 $0.56 2
28 4318-002 Ground Cable #2 x 2' $16.24 1
29 8104-006 Screw .31 x 1 $0.56 1
30 4319-002 Heat Shrink $1.68 1
31 4318-001 Battery Cable #2 x 2' $20.94 1
32 4301770 Circuit Breaker $80.64 1

15.
 TROUBLESHOOTING GUIDE
ST22/31ET
Test Equipment: 1. 0-5000 psi pressure gauge
2. DC voltmeter/ohm meter
3. DC amp meter
4. standard mechanics tools

Note: Please refer to the electrical diagrams and hose connection drawings in the liftgate’s
owners manual when troubleshooting. This guide is only for standard Thieman liftgates.
Special liftgates with options other than those in the owner’s manual will require special
diagrams for troubleshooting. Read and understand this entire guide completely before doing
any troubleshooting. Certain listed problems may be related to other problems listed so a
comprehensive knowledge is required before proceeding.

1. Problem - Pump motor will not run in the raise mode

Causes - a. Tripped circuit breaker
b. Defective or undercharged battery(ies)
c. Improper battery cable connection or improper ground connection
d. Defective or improperly wired raise switch
e. Defective or improperly wired solenoid start switch
f. Defective pump motor
Corrections - a. Reset the circuit breaker located within 2ft of the liftgate supply
battery(ies).
b. The “at rest” voltage for the batteries without the engine running and under
no load should be at least 12.5V. The minimum voltage between the motor
stud and ground is 9V at maximum load conditions. If proper voltage is not
present, charge or replace the batteries. The battery(ies) on the vehicle
should be that which has a minimum 150 amp reserve capacity.
c. Trace battery and ground cable connections to locate improper
connection(s). Make sure the ground cable is installed going from the
aluminum pump base to bare metal on the truck frame. Make sure the
ground cable from the batteries to the frame is a heavy 2ga. cable and that
it too is connected to bare metal on the frame. Make sure there is 12.5V
present at the large terminal on the motor start solenoid where the 2ga.
cable from the batteries is connected. Replace any damaged cables and
repair any bad connections.
d. Check for voltage on the black wire at the control switch. If no voltage is
present the black wire from the motor start solenoid is loose or broken and
needs repaired. If voltage is present then check for voltage at the green
and white wire on the switch with the switch in the “RAISE” position. If no
voltage is present, replace the switch.
e. Check for voltage on the white wire at the motor start switch when the
switch is activated. If no voltage exists the white wire is loose or broken
between the switch and the motor start solenoid. Check that the purple
ground wire on the start solenoid is connected properly and there are no
bad connections. If there is voltage on the white wire and the coil does not
energize or if there is no voltage present at the motor terminal then replace
the start switch.
f. With the switch activated in the “RAISE” position and the motor start
solenoid is activated, check for voltage at the motor terminal. If voltage is
present and the motor is not running, replace the motor.

2. Problem - Liftgate will not raise to bed with a load and the pump motor running

16.
 Causes- a. Low hydraulic fluid
b. Overload condition
c. Improperly adjusted or defective main relief valve
d. Lift cylinders are bypassing, liftgate is drifting down
e. Broken hydraulic line
f. Clogged or disconnected suction line
g. Defective pump
Corrections - a. Make sure the reservoir has the proper amount of fluid. Either check for
the fluid line through the plastic reservoir or for metal reservoirs remove
the breather cap and check the fluid line through the fill hole. The hydraulic
fluid should be within 1/2" of the top of the reservoir with the liftgate in the
lowered position. Fill with Dexron III automatic transmission fluid.
b. The power unit on the M is equipped with a lifting relief valve to prevent
overloading of the liftgate. The relief settings should be as follows:
ST22-2200PSI
ST31-2200PSI
c. See section “c” above for relief valve setting. Plumb a pressure gauge into
the high pressure circuit of the liftgate. Remove all loads from the liftgate’s
platform. Engage the “RAISE” switch until the liftgate is fully raised. Keep
the “RAISE” switch engaged until the pump bypasses through the relief
valve and note the pressure on the gauge at this time. If the rated relief
pressure is not present during relief, adjust the high pressure relief valve
setting as necessary. If the relief pressure is not attainable the relief valve
must be cleaned and/or replaced or the pump is defective. See part “g”
below.
d. If the liftgate will not raise with a load on the platform but empty is raising
slowly or only partially, the cylinder(s) may be bypassing. To check for a
bypassing cylinder(s) do the following. Lower the gate to the ground to
relieve all pressure from the cylinder(s). Disconnect the cylinder(s) from
the liftarm. Press the “RAISE” switch until the cylinder(s) is fully retracted.
Disconnect the return line from the power unit and put the end of the line in
a container to catch any oil which comes out during this test. Press the
“RAISE” switch for 15 to 20 seconds and watch for a steady stream of fluid
coming out of the return line into the container. If no steady stream of oil is
present connect the hose to the butt end of the cylinder(s) after removing
the return line and fitting. Re-attach the return line and fitting to the rod end
port. Put the loose end of the return line in a container to catch any oil,
which comes out during this test. Press the “RAISE” switch until the
cylinder(s) is fully extended. Press the “RAISE” switch for 15 to 20
seconds and watch for a steady stream of fluid coming out of one of the
disconnected hose ends into the container. Replace or rebuild any cylinder
with fluid coming out of the return line, as this indicates fluid is bypassing
the piston seals on the cylinder. Reconnect rebuilt or replaced cylinder(s)
and hoses as before.
e. Broken or punctured hydraulic lines and fittings must be replaced with care
to avoid injury from high pressure oil streams.
f. With the liftgate at the ground, disconnect the power unit and remove the
reservoir. Check to see if the suction tube is clogged or has fallen out of the
pump base. Clean the screen or reattach the suction tube as required.
g. If all else fails replace the power unit, it is probably worn out.

3. Problem - Liftgate will not lower

Causes - a. Defective lowering solenoid coil or valve

17.
 b. Clogged or defective hydraulic lines, fittings or flow controls
Corrections - a. With the “LOWER” switch engaged check for voltage on the green wire at
the switch. If no voltage is present replace the switch. If voltage is present,
with the “LOWER” switch engaged, check for voltage at the green wire on
the lower solenoid valve coil terminal. If no voltage is present, the green
wire from the “LOWER” switch is loose or broken and needs replaced. If
there is voltage (minimum of 9.5 volts) and the valve is not opening to
allow the gate to lower, either the lower coil is bad or the entire lower
coil/valve assembly is bad. To check to see if the coil is defective, remove
the green wire from the spade terminal on the lower coil and check for
continuity between the spade terminal and the nut, which holds the coil on
the valve stem. If continuity does not exist, replace the defective coil,
otherwise replace the defective lower coil/valve assembly.
b. Remove any obstruction in the hoses, fittings or flow controls or replace
any hose, fitting or flow control, which does not allow fluid to flow through
freely.

4. Problem - Liftgate raises slowly - The raise speed of the ST22/31 on a 56” bed height while
empty at 70° F is approximately 10-15 seconds. The raise speed loaded for the
same conditions is approximately 21-28 seconds. These speeds vary with each
model.
Causes - a. Overload condition
b. Cold weather
c. Partially blocked suction screen
d. Lift cylinders are bypassing
e. Improperly adjusted or defective raise relief valve
f. Low voltage and/or bad ground
g. Worn out pump
Corrections - a. See section 2b
b. Refer to Owner’s Manual for alternative oils to use for cold weather
conditions.
c. Remove reservoir and clean or replace suction screen as necessary.
d. See section 2d
e. See section 2c
f. The minimum voltage between the motor stud and ground is 9.5 volts at
maximum load conditions. See section 1b and 1c
g. After all other corrections are performed it will be necessary to replace the
pump.

5. Problem - Foamy oil flowing from reservoir breather

Causes - a. Air is present in the system
Corrections - a. This can occur if air enters the system if the fluid level is low, see problem
2, part a, or if the suction tube is disconnected, see problem 2, part f. Also
air may enter through fittings, which are not tightened properly, so check
for any leaks around fittings or hoses. Once the source of the air is
determined, the cylinders must be bled of all air. Most air can be removed
from the system by lowering the gate to the ground to relieve all pressure
from the cylinders, unpinning the cylinders and cycling them back and forth
several times from fully extended to fully retracted and allowing the pump
to bypass through the relief valves for a few seconds in each direction.

If you have any questions or problems that are not covered in this guide please call Thieman’s
Engineering Department at 1-800-524-5210.

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