on shaft.
4. Is hub clean and do friction discs slide
freely.
5. Are controls which govern start of braking
cycles operating properly?
6. Are limit switches, electric eyes, etc.
functioning properly?
7. On vertically mounted brakes, are springs
in place of disc pack? See
P/N 8-078-937-05 (Sheet 301.3).
8. If brake is floor mounted, check alignment.
See Section I, Step E.
9. Pressure spring may be improperly
assembled or broken.
10. Is solenoid air gap adjusted correctly? See
Self-Adjust Maintenance
, Section IV, Item
C.
11. Check linkage for binding. The approximate
pressure applied to the top of the solenoid
link to move plunger is:
If excessive force is required, determine
cause of binding and correct. Do not
overlook bent, worn or broken plunger
guides as a possible cause for binding.
12. Solenoid lever stop (22) must be in place
on support plate.
13. Solenoid may not be energizing and
releasing the brake. Check voltage at
the coil and compare to the coil and/or
nameplate voltage rating.
14. Whether brake is AC or DC a voltage drop
may be occurring. If excessive drop in
voltage is noted, check wire size of power
source. Correct as needed.
Note
: A method to check voltage at coil is
to insert a block of wood of the approximate
thickness of the solenoid air gap between
the solenoid frame and plunger. (The block
will prevent brake from releasing when coil
is energized.) Connect voltmeter leads at
the coil terminals or lead wires. Energize
coil. Voltmeter needle will not fluctuate and
reading can be taken. Reading should be
taken immediately and the coil de-energized
to prevent overheating of the coil. Compare
voltage reading with coil rating.
15. If brake is DC solenoid style, check switch
actuation and condition of coil. The switch
should open with the following approximate
air gap. (This is plunger travel remaining
before plunger seats to frame.) Solenoid
size is used for reference:
If actuating arm is bent, replace plunger.
Check switch contacts. If pitted, replace
switch.
16. Check slots of endplate for wear at the
areas where stationary discs are in contact.
Grooves in the slots can cause hang-up or
even breakage of ears of stationary discs.
If grooving is noted, replace endplate.
17. Check that heads of mounting bolts do not
extend above wear surface of endplate.
18. On vertical brakes with cast iron end-
plates, check the vertical mounting pins
to be sure shoulder of pin is flush with
wear surface of endplate. Be sure pins are
straight and pressure plate and stationary
disc(s) are free to slide on the pins. Be
sure springs and spacers are installed in
proper order. See P/N 8-078-937-05
(Sheet 301.3).
19. Check pressure spring length to insure
correct compressed height. Original spring
lengths are given in the following Table
so that correct setting may be verified
and corrected if necessary. With worn
friction discs, add amount of wear to the
approximate spring length shown.
20. If a heater is supplied and excess rusting
has occurred in brake, check power source
to heater to be sure it is operating and that
heater is not burned out.
21. If stopping time is more than two seconds
(rule of thumb), the brake torque rating
may be insufficient. If the brake stops high
inertial loads and/or brake stops more
than five times per minute, check thermal
requirements of application versus thermal
capacity rating of brake.
22. Use Loctite® 242 to secure link screw
nut (13N) to link screw (13C) if vibration
causes nut to loosen.
B. If brake hums, solenoid pulls in slowly,
or coil burns out, check the following:
1. Voltage supply at coil versus coil rating.
2. Is solenoid air gap excessive? See
Self-
Adjust Maintenance.
3. Shading coils may be broken.
4. Plunger guides may be excessively worn.
Does solenoid plunger rub on solenoid frame
laminations? If so, replace plunger guides.
5. Solenoid frame and plunger may be
excessively worn.
6. Is solenoid dirty?
7. Solenoid mounting screws may have
become loose, causing frame to shift and
plunger to seat improperly.
8. Sector gear and pinion teeth may be
jamming due to excessive tooth wear.
9. Excessive voltage drop when motor starts.
Check size of lead wires for motor starting
current and solenoid inrush current. See
Section V-A, Items 11, 12, 14 and 15.
C. If brake is noisy during stopping:
1. Check mounting face runout, mounting
rabbet eccentricity and shaft runout. See
Installation Procedure
, Section I, Step E.
Correct as required.
2. Check for signs of the outside diameter
of the friction disc(s) rubbing on the inside
diameter of the endplate. This would indicate
brake is eccentric with respect to the motor
shaft and/or the shaft is deflecting during a
stop. Check alignment and shaft diameter.
Also check for worn motor bearings. If
realignment does not correct the problem, a
larger diameter shaft may be required. Shaft
deflection may also be caused by excessive
overhang of brake from motor bearing.
Additional shaft support may be required.
3. In cases where motor shaft extends through
a fan casing or guard, the clearance hole
may not be adequate. Rubbing of the shaft
may occur causing a noise during a stop. If
required, enlarge clearance hole.
4. Check for bad motor bearings. Replace
if necessary. Check for excessive shaft
endfloat. Correct as required.
7/32” to 1/4”
#6 solenoid
3/16” to 7/32”
#5 or #8 solenoid
3-1/4”
35, 75 & 105
Purple
3-1/4”
25 & 50
Orange
3-1/4”
15
White
3-1/4”
10
Black
3-3/8”
35, 75 & 105
Green
3-3/8”
25 & 50
Red
3-9/16”
15
Yellow
3-5/16”
10
Blue
Compressed
Spring Length
Torque
(lb-ft)
Color
Copyright© 2000-2017 by Rexnord Corporation
Rexnord Corporation, Stearns Division, 5150 International Dr., Cudahy, Wisconsin 53110, (414) 272-1100 Fax: (414) 277-4364 www.rexnord.com/stearns
16 lbs
#8 coil
9 lbs
#6 coil (25 lb-ft)
5-1/2 lbs
#6 coil (15 lb-ft)
3 lbs
#5 coil
