M925a2 brakes are staying engaged

We are a small Vfd and just received a 91 model m925a2. The brakes on the unit will lock up or stay engaged after the foot brake peddles is pushed about 5 times also the brake lights stay on. I can loosen the line on the brake light switch and the truck will drive fine. Anyone have any ideas

thanks

I wouldn't drive the truck while you're having a problem like this . I think your spring brakes will lock when there's no air pressure

Check the front passenger side gladhand to see if it has a valve on it, if it does take it off there is not supposed to be one on that gladhand and the cover is supposed to be vented.

What are the pressures on primary and sec gauges reading after the 5 pumps.

over 100

Roxtonvfd said:

over 100

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Did you check that gladhand?

I will tonight when get off

Thanks

Csm Davis said:

Check the front passenger side gladhand to see if it has a valve on it, if it does take it off there is not supposed to be one on that gladhand and the cover is supposed to be vented.

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Thank you very much that's all it was
We owe you big time

You just keep safe and that's thanks enough.

Man I wish my problems were that easy!

Looking for more help with our truck

the truck seems to have no electrical power no lights of any type will work and the truck will not even try to crank
the oBly noise it will make is a clicking from the PCB box ( I think that's what it's called ) it. On the fire wall in front of driver seat by the jug

I checked the voltage on the batteries today and without removing cables my volt meter read 15.7. I would think that is low.

i guess my my questions is does that box control all the voltage to the truck lights and all or do I have something else wrong

Yes it does , it has two solenoids in it first check wiring then if needed replace solenoids they can be ordered from Napa, aslo make sure when you check batteries you are going from negative of first battery to pos of last , it should be 24, 25 volts

Yes that is way to low. My truck did the same thing. I lost two batterys and had to replace. Could have run on two but I like 4 it starts so much better

Thanks everyone. I checked the batteries and had one bad in each string
replaced and it still didon't crank Jumped the starter and the lights on the dash came on so I'm guessing the pcb box is bad also you cou,d hear the box click when I jumped the starter


if you flip the switch several time know the truck will crank

again thanks for the help this is twice you have helped