Bendix Commercial Vehicle Systems SL-3, SL-4 User Manual

Bendix® SL-3™ & SL-4™ Stop Light Switch

SD-06-1800

MACHINE
SCREWS

7

TERMINAL 2

COVER 1

TERMINAL

CONNECTOR 7

CONTACTS

PLUNGER 4

BODY

FIGURE 1 - SL-3™ STOP LIGHT SWITCH

DIAPHRAGM 6

SPRING 3

WASHER 5

DESCRIPTION

The stop light switch is an electro-pneumatic switch and
operates in conjunction with the brake valve and stop lights
by completing the electrical circuit when a brake application
is made.

CONTACT

PISTON

13

O-RING

DIAPHRAGM 14

FIGURE 2 - SL-4

TERMINAL 9

™

STOP LIGHT SWITCH

VENT PLUG 10

COVER 8

SPRING 11
CONTACT

STRIP 12

GASKET

15

BODY

PREVENTIVE MAINTENANCE

Important: Review the Bendix Warranty Policy before

performing any intrusive maintenance procedures. A warranty
may be voided if intrusive maintenance is performed during
the warranty period.

OPERATION

When a brake application is made, air pressure from the
brake valve enters the cavity below the diaphragm. At
approximately 5 psi, the air pressure underneath the
diaphragm overcomes the force of the spring and moves
the piston or plunger until the contact points close completing
the stop light electrical circuit and lighting the stop lights.

No two vehicles operate under identical conditions; as a
result, maintenance intervals may vary. Experience is a
valuable guide in determining the best maintenance interval
for air brake system components. At a minimum, the SL-3™/
SL-4™ switch should be inspected every 6 months or 1500
operating hours, whichever comes first, for proper operation
and electrical connections. Should the SL-3™/SL-4™ switch
not meet the elements of the operational tests noted in this
document, further investigation and service of the valve may
be required.

1

TESTING FOR SERVICEABILITY

OPERATING TEST

1. Apply the brake valve and note that the stop light lights
before the delivery pressure reaches 7 psi.

2. Release the brake valve and note that the stop light goes
“off”.

LEAKAGE TEST

1. With the brakes fully applied, no leakage is permitted at
the stop light switch. If the stop light switch does not
function as described or if leakage is excessive, it is
recommended that it be replaced with a new unit or
repaired with genuine Bendix parts available at authorized
Bendix parts outlets.

CLEANING AND INSPECTION

Clean all metal parts in cleaning solvent. Wipe rubber parts
dry with cloth.

Inspect contact points for pits or wear. If pitting is not too
severe, the points may be reconditioned by filing with a
distributor point file. If points cannot be reconditioned, they
should be replaced. The contact strip in the SL-4™ switch
may be turned over to use the other side of the contacts.

Check the spring for signs of deterioration; Replace if
discolored. The spring in the SL-3™ switch carries the current
of the electrical circuit involved; consequently , in the case of
excessive current, as might be caused by a short, the spring
will be overheated and ruined.

REMOVING

1. Disconnect electrical connections at the stop light switch.

2. Disconnect air line to the stop light switch.

3. Remove the stop light switch.

INSTALLING

1. Install in a convenient location for servicing.

2. Install with pipe tap pointing to the ground and keep it
high for adequate drainage.

3. Connect the stop light switch in series in the stop light
circuit.

4. Keep the stop light switch terminals away from frame
members to avoid grounding.

5. Connect the pipe tap to the brake chamber supply line
so that the stop light switch will operate whether the
foot or hand valve is applied.

DISASSEMBLY

(SL-3™ SWITCH)

1. Place hex portion of body in a vise.

2. Using a large end wrench on cover flats, turn cover (1)
in a counterclockwise direction and remove from body .

3. Remove terminal nuts, terminals (2) and terminal
connector (7) from cover.

4. Remove spring (3), plunger (4), washer (5) and
diaphragm (6) from body.

(SL-4™ SWITCH)

1. Remove two machine screws (7) and remove cover (8).

2. Remove terminal nuts and terminals (9) from cover.

3. Remove the vent plug (10) from cover.

4. Remove spring (1 1), contact strip (12), piston (13) and
o-ring diaphragm (14) from body .

Inspect cover and body. If cracked or damaged, replace.
Only genuine Bendix service parts should be used for

replacement.

ASSEMBLY

(SL-3™ Switch) (Figure 1)

1. Insert terminal screws (2) in cover (1), making sure the
terminal connector (7) is properly positioned.

2. Secure terminal screws with washers and nuts, or
terminal clips, as the case may be.

3. Place diaphragm (6) in body.

4. Position contact plunger (4) on diaphragm.

5. Position spring (3) on plunger.

6. Place washer (5) on diaphragm and screw cover (1)
into body. Torque to 30 foot pounds. Make certain the
vent hole in the cover is open.

(SL-4™ Switch) (Figure 2)

1. Position terminals (9) in cover (8) and secure with washers
and nuts or terminal clips. Place vent plug (10) in cover .

2. Place o-ring diaphragm (14) and piston (13) in body.
O-ring diaphragm should be installed with its flat side
adjacent to the piston.

3. Place gasket (15) in place on body and contact strip
(12) on piston (13).

4. Position cover assembly on gasket and secure with
machine screws. Torque to 20 inch pounds.

TEST OF REBUILT STOP LIGHT SWITCH

Both operating and leakage tests, as indicated under section
headed “Testing for Serviceability”, must be made after
rebuilding or repairing the stop light switch. The switch must
meet the following specifications;

1. No leakage is permissible at the stop light switch with
the brakes applied.

2. The stop light switch contact should close with not more
than 7 pounds of air pressure.

2