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MC 9 Parking brake problems Keith 2-26-03  
Wondering if anyone might have had this problem before and could help. I have a 1983 MCI 9 bus that I am doing the conversion on. We are traveling in it as well. Sometimes we can stop somewhere and the parking brake doesn't hold. The air pressure is up where it needs to be and everything seems normal. The brakes were just checked out and they seem to work great when we are stopping. It is just the parking brake and it is only sometimes. Other times it will lock in and hold.

Another clue may be that when the parking brake is acting up the bay door air switch seems to vent differently when you hit the switch. Instead of just the hit of air that you normally hear, you hear a constant air release and the button don't stay in.

Any hints would be appreciated.
GOODSON BUS BOBBY 4-13-17  
Recently installed 4 rear drive axle air bags w/ plates,Also new hose lines to air bags,Lastly installed right & left rear leveling valves,Upon air up air gage stays stuck at 90 psi and will not unlock parking brake,Tried performing brake service check but no results--still stays at 90 psi,On cold start air reaches 90 psi quickly so I presume air compressor is in satisfactory & operating condition,Can anybody assist ??,Thanx BOBBY robertloya11@yahoo.com Vehicle: '83 MC 9 8V71 Detroit Diesel 5spd
GOODSON BUS BOBBY 4-13-17  
Recently installed 4 rear drive axle air bags w/ plates,Also new hose lines to air bags,Lastly installed right & left rear leveling valves,Upon air up air gage stays stuck at 90 psi and will not unlock parking brake,Tried performing brake service check but no results--still stays at 90 psi,On cold start air reaches 90 psi quickly so I presume air compressor is in satisfactory & operating condition,Can anybody assist ??,Thanx BOBBY robertloya11@yahoo.com
Re: MC 9 Parking brake problems Joe 2-26-03  
It sounds like one of your tanks isn't getting fully aired up all the time. As the main tank fills up, at about 60psi air opens a check valve or valves and fills a secondary tank or tanks. Sometimes the check valve goes bad and the one or the other secondary tanks doesn't fill up. Then you have a low air tank, but the main is full so it shows like everything is normal but it isn't. See how many tanks you have.
Re: MC 9 Parking brake problems Keith 2-28-03  
I couldn't find out how many tanks we have. How would we check this out and correct it if it shows to be bad?

Would that also account for the bay lock release acting the way it does? It seems as though maybe there is some type of valve or something that isn't engaging when you set the parking brake switch. If I remember right the bays won't open unless the parking brake is set and this might have something to do with that problem.

What is the common link between the bay switch and parking brake switch? Being brand new to buses I'm not sure how this system works.

Thanks for your input.
Re: MC 9 Parking brake problems Joe 3-2-03  
You will have to trace the air lines from the compressor. Then follow the air line or lines. I don't know your particular set up as some are set up for local and some are set up for over the road. I'm assuming that yours was a local. That has a holding brake as well as a parking brake. Either one the door won't open unless the holding or parking brake is on. Somewhere there is a bypass to that. Again, I couldn't tell you where to look for it. Possibly your holding brake is loosing air, or doesn't have a good enough supply of air to hold the brake, and I believe the system needs 60psi to hold the door valve in.
Re: MC 9 Parking brake problems Keith 3-4-03  
Thanks. I'll check all this out and when I find something I'll come back and post the results.
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