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Air and Brake lights stay on


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My 1985 MH600 has been seating for two years. Recently, i started the truck to drive around but the air and brake lights stay on and will not die off. Also when i put it in either reverse nor drive, the truck will not move. Any idea why this happening?

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Good point hat. I was "assuming" (I know - ass you me) that he had sufficient air pressure. If there is not enough air pressure the parking valves will "pop out" instead of staying "in". The valves need to stay "in" to release the brakes.

I had an MH that after it sat for a few weeks or months would not release the brakes. I would "jack" around with the foot treadle and try to move the truck forward and backward and finally they would release. Seems the pads would stick to the drums.

Be careful when trying to move the truck forward/backward, you could twist the driveshaft or break a u-joint/yoke.

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PRR Country and Charter member of the "Mack Pack"

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  • 3 months later...
  • 3 weeks later...

If the air pressure light and brake lights are on its gotnlow air pressure at the switch and if the brakes won't release its either low pressure or they are stuck. When you try to move it does the brake knob stay depressed on the dash? If not there isn't enough air to release the brakes. If so make sure your getting air to the brake chambers by removing an emergency line from a brake chamber and have someone release the parking brakes and make sure you have air at the line. If there is air at the chambers and the knob stays in on the dash smack the back edge of the brake drum with about a 3-5# hammer with the brakes released and the wheels chocked, if they are stuck to the drum that should break them free.

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