NMC-WOLLARD 2021Truax Blvd., Eau Claire, WI 54703, Phone (715) 835-3151, Fax (715) 835-6625
M140 Tow Tractor Manual No. 46054
PAGE 2-11
CHAPTER 2 MAINTENANCE
2 TROUBLESHOOTING
AUGUST 31, 2008
2.4.1 Equalizer Valve
The equalizer valve reduces the hydraulic pressure to the front disk brakes
and maintains high pressure to the rear drum brakes.
Check the equalizer valve for leakage whenever the brakes are serviced. If
there is evidence of leakage, replace the equalizer valve.
2.4.2 Check Valve
The check valve maintains a slight pressure in the rear brake system to
prevent the entry of air into the system past the wheel cylinder cups when
cylinder.
The check valve is non-repairable. If air is frequently being drawn into the
brake system, as evidenced by spongy brakes, replace the check valve.
2.4.3 Stoplight Switch
The stoplight switch is actuated by hydraulic pressure. It is located next to the
Check switch operation by inspecting brake lights while brake is being
applied. Lights should come on with very mild pressure on the brake pedal.
If one light does not come on, check for a burned-out bulb or a poor electrical
connection. If both lights do not come on, check the fuses.
If bulbs, fuses, and connections are good, check the stop light switch: Unplug
the two wires from the switch and test for 12VDC. Voltage should be present.
If not, the problem is in the wiring. If voltage is present, the switch is not
working and should be replaced.
If care is taken, a new switch may be installed without allowing air into the
brake system. To replace the switch, unscrew the switch from the hydraulic
new switch. Plug in the wires and re-check the brake light operation.
If brakes feel spongy after replacing the stoplight switch, bleed the brakes
according to paragraph 2-1 - 1.10.
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