Stearns 81000 Series Installation and Service Instructions

®

Spring-Set Disc Brakes

Installation and Service Instructions
for Self Adjust Brakes
81,000 Series

Tools required for installation and servicing:

3/8” hex wrench 5/16” nut driver
5/16” hex wrench 1/4” screwdriver
3/16” hex wrench 8” adjustable wrench

P/N 8-078-921-00

effective 09/20/10

Current revision available @

Figure 1

Important

Please read these instructions carefully before
installing, operating, or servicing your Stearns
Brake. Failure to comply with these instructions
could cause injury to personnel and/or damage
to property if the brake is installed incorrectly.
For definition of limited warranty/liability, contact

Stearns Div.,

Cudahy, WI 53110, (414) 272-

1100.

Caution

1. Installation and servicing must be made in
compliance wit all local safety codes including
Occupational Safety and Health Act (OSHA).
All wiring and electrical connections must
comply with the National Electric Code (NEC)
and local electric codes in effect.

2. Use of this brake in atmospheres containing

explosive gases and dusts must be in
accordance with NEC article 501. This brake
is not suitable for use in certain atmospheres
containing explosive gases and dusts. HazLoc
inspection authorities are responsible for
verifying and authorizing the use of suitably
designed and installed HazLoc equipment.
When questions arise consult local Authority
Having Jurisdiction (AHJ).

3. To prevent an electrical hazard, disconnect
power source before working on the brake.
If power disconnect point is out of sight,
lock disconnect in the off position and tag to
prevent accidental application of power.

4. Make certain power source conforms to
the requirements specified on the brake
nameplate.

5. Be careful when touching the exterior of an
operating brake. Allow sufficient time for
brake to cool before disassembly. Surfaces
may be hot enough to be painful or cause
injury.

6. Do not operate brake with housing removed.
All moving parts should be guarded.

7. Installation and servicing should be performed
only by qualified personnel familiar with the
construction and operation of the brake.

8. For proper performance and operation, only
genuine Stearns parts should be used for
repairs and replacements.

9. After usage, the brake interior will contain
burnt and degraded friction material dust
into the air or inhaling it, as this may be
dangerous to your health.

10. DO NOT BLOW OFF DUST using an air
hose. It is important to avoid dispersing dust
into the air or inhaling it, as this may be
dangerous to your health.

a) Wear a filtered mask or a respirator
while removing dust from the inside of
a brake.

b) Use a vacuum cleaner or a soft brush
to remove dust from the brake. When
brushing, avoid causing the dust to
become airborne. Collect the dust in a
container, such as a bag, which can
be sealed off.

11. Caution! While the brake is equipped with a
manual release to allow manual shaft rotation,
the motor should not be run with the manual

release engaged, to avoid overheating the
friction disc(s).

General Description

This series brake is spring-set, electrically
released. They contain two or three rotating
friction discs (4) driven by a hub (16) mounted on
the motor or other shaft.

Note: Fan-guard mounted brakes requiring IP54
& IP55 protection may require additional sealing
measures beyond seals provided with this brake.
Pressurized sprays aimed at the fan and brake
hub surfaces can result in fluid migration along the
motor shaft and keyway, and into the brake. The
use of an appropriate sealant such as RTV or a
forsheda seal is advised.

Operating Principle

This series contains two or three friction discs
(4) assembled alternately between the endplate
(2) friction surface, stationary disc(s) (3) and
pressure plate (5). The stationary components
are restrained from rotating by being keyed into
the endplate. With the brake released, all disc
pack components are free to slide axially and the
friction disc(s) to rotate.

Brake release occurs when the solenoid coil
is electrically energized, causing the solenoid
plunger to travel a specified distance and through
a lever system, overcoming the pressure spring
force. This action released the clamping force on
the disc pack, thereby allowing the friction disc(s)
and brake hub to rotate.

Brake sets and torque is produced when electric
current to the solenoid coil is interrupted,
thereby collapsing the solenoid magnetic field.
The solenoid plunger returns to its original
de-energized position allowing the lever arm to
move forward by virtue of the compressed torque
springs. This action compressed the disc pack
components which applies a retarding torque to
the brake hub and ultimately restores the brake to
a spring-set condition.

BRAKE MOUNTING

Remove manual release knob.
Remove housing screws.



Remove housing.

Lift off support plate.



Remove disc pack.

counter­clockwise

A. Push plunger down.
B. Pull manual release to hold plunger.



C. Remove support plate screws.

counter­clockwise

A. Position endplate on motor register.
B. Insert four mounting bolts and tighten.



(Torque per manufacturer specification)

A. Position hub on shaft as shown.
Tighten set screws to motor shaft.



Torque to: 5/16” - 156 lb-in;
3/8” - 288 lb-in;
1/2” - 625 lb-in.
B. Reassemble disc pack in reverse*
order of removal.

AC coils are 50/60 hz,
single phase rated. Power



supply to coil must not
have current or frequency
limiting output that is less
then the coil requirement.
Voltage supply to the coil
must be within ±10% of
nameplate rating.*

Caution: Keep wiring
away from pinch points.

A. Route lead wires through conduit hole.
B. Position support plate on endplate.



C. Insert six mounting screws with lockwashers;
tighten to 85-100 lb-in.

clockwise

Replace housing.
Tighten housing screws to 130 lb-in and release



knob to 50 lb-in.

clockwise

* For DC voltages see

sheet 8-078-950-00.

2

General Maintenance
Warning! Any mechanism or load held in position

by the brake should be secured to prevent
possible injury or damage to equipment before
any disassembly of the brake is attempted or the
manual release knob or lever is operated on the
brake. Observe all cautions listed at the beginning
of this manual.

Note: Do not lubricate any part of the brake as
this may cause a malfunction and/or a loss of
torque.

Troubleshooting

A. If brake does not stop properly,

coasts or overheats:

1. Check that manual release knob is not in
released mode.

2. Check for excessively worn, charred or
broken friction discs.

3. Check that hub has not loosened and
shifted on motor shaft.

4. Check that friction discs slide freely over
hub. Clean hub and/or file burrs and nicks
if required.

5. Check that stationary disc(s) and/or
pressure plate can move freely in endplate
and that they are not warped from
overheating.

6. Check endplate slots for wear in the areas
where stationary disc(s) and/or pressure
plate make contact. Grooves in slots can
prevent free disc movement and result in
torque loss, stationary disc or friction disc
breakage.

7. On vertically mounted brakes, check that
springs are installed correctly and that
stationary disc(s) can slide freely over
vertical mounting pins. Check for wear on
plunger guide bracket.

8. Confirm that the pressure spring nut (19)
is properly tightened against the spacer
(134) under the nut. Spring length should
be measured from the cast surface of the

support plate to the bottom side of the
spring nut. Spring lengths are based on
the brake fully assembled, using a new
disc pack. Spring length will increase as
the disc pack wears.

Torque

(lb-ft)

Compressed

Spring Length

125 4-23/32”
175 4-23/32”
230 4-27/32”

9. Check solenoid air gap (see page 4).
Adjust if necessary.

10. Check that solenoid linkage can move
freely. It requires approximately 18 lbs of
pressure on the 125 lb-ft; 23 lbs on the
175, and 230 lb-ft to seat solenoid plunger
correctly functioning brake.

11. Check voltage reading at coil terminals
against coil voltage rating.

12. Check that brake coil is energized at
the same time as, or prior to, motor and
de-energized at the same time, or after,
motor.

13. If stopping time exceeds 1 second, or if
the application requires more than five
stops per minute, check the thermal
requirements to stop load against the
thermal capacity of the brake.

14. Check for excessive voltage drop in
motor line when motor is started. check
wire gauge of supply line against motor
starting current and solenoid inrush
current. Measure voltage drop at solenoid
coil terminals during maximum inrush
current condition. To accomplish this,
insert a block of wood, or other non­magnetic material, between solenoid
plunger and frame. Block thickness should
approximately equal solenoid air gap.
Energize motor and brake simultaneously,

take reading and immediately shut down.
This is to prevent motor, brake or solenoid
burnup.

B: If brake hums, solenoid pulls in slowly, or

coil burns out:

1. Check Items A-7, A-9, A-11 and A-14.

2. Check if shading coils are broken.

3. Check for worn plunger guides or
if plunger rubs on solenoid frame
laminations.

4. Check for worn solenoid plunger and
frame.

5. Check if solenoid is dirty.

6. Check if solenoid mounting screws have
loosened.

7. Check for worn or binding linkage. For
normal pressure required to seat solenoid
plunger to frame see A-10.

C: If brake is noisy during stopping and/or

friction discs shatter:

1. Check for worn motor bearings allowing
shaft runout.

2. On foot mounted brakes, recheck
alignment.

3. Check hub position on shaft. The outboard
face of hub should protrude 3/32” to 1/8”
beyond face of outboard friction disc.

4. Check motor shaft endfloat. It should not
exceed 0.020”.

5. Check concentricity of endplate and
C-face register. Alignment must be within
.007” concentricity and face runout. Shaft
runout should be within .002” TIR.

Vertical Brake Assembly

Refer to service sheet 8-078-931-05 and
8-078-931-15 for proper spring and spacer
positions when brake is assembled for vertical
orientation.

3