Parking Brake MCI-9

Kwajdiver · February 28, 2009, 08:35:51 AM

Now that transmisson is not a problem, I have a new problems, (isn't that how it always is). Went to set the parking brake after returning from the getting the tranny serviced, went to set the (air) parking brake and it's didn't want to set and making all kinds of air noises. Did get it set,, then I heard air escaping under the bus.

Last year I replaced the air switch, the one that sets the brake. Also replace, forget what you call it, the air tank looking thing between the front wheels.

Guessing the air switch may have gone bad again.

Thanks for the input.

Bill

JackConrad · February 28, 2009, 08:56:55 AM

Bill,
1st step is to determine exactly where the air is leaking. Could be one (or more) of several places. You may have a leaking DD3 parking diaphragm on the drive axle. This can backfeed air and cause air to leak from other places. Clamp the DD3 rubber air line on each drive axle (one at a time) and see it that changes the air leakage. Jack

buswarrior · February 28, 2009, 09:42:40 AM

While you are under there, pay attention to the inversion valve, mounted above the differential with some of the brake chamber hoses running to it.

It's the guts of the parking system changing from parked to go, and is considered a preventive maintenance item to be changed for reliable parking system functionality.

There should not be any air leaking from it's exhaust except when you activate the control knob up at the driver's position.

happy coaching!
buswarrior

Kwajdiver · February 28, 2009, 01:55:07 PM

Not going to be able to get under the bus,,, Did try, but without blocks and a jack,,,,,,,,,

The air switch (parking brake) doesn't seem to operate correctly. Doesn't seem to have the movement it once had. The inverison value is located in the side door under the driver?

? Checked it, it's not leaking. This only seems to come in play when I try to pull the parking brake.

Thanks for the help.

Bill

Sammy · February 28, 2009, 02:51:07 PM

I would build up air pressure to 120psi with parking brake "OFF"- hold service brake or chock wheels so bus won't roll. Your park brake valve button feels different because you have an air leak in park brake air circuit.Once bus has been fully aired up, shut off engine - less noise. Step to rear of bus on either side and listen for an air leak by the drive axle with brake released. If no air leak is heard have someone else apply the service brake while you are still listening for a leak.If no leak have the assist try to apply parking brake while you listen for leaks.DO NOT GO UNDER THAT BUS without proper jacks and supports. Might have blown an air line, could be something as simple as that. Jack's advice is right on the money, AFTER you can get under the bus SAFELY.

bobofthenorth · February 28, 2009, 04:38:30 PM

Where are you Bill?

buswarrior · February 28, 2009, 09:50:02 PM

What vintage is your MC9?

Inversion valve is back above the differential.

What under the driver are you checking?

There is the shuttle valve to fulfill some of the air failure requirements, unique to a modern DD3 system, there is the brake valve controlled by your foot....

keep typing,we'll get to the bottom of this!

happy coaching!
buswarrior

Kwajdiver · March 01, 2009, 08:14:22 AM

This is really dumb. The cover that protects the braking button, had a screw coming out. Which was preventing the button from it's full motion.

Removed the cover, and all is well.

Thanks for all the input.

Bill

JackConrad · March 01, 2009, 08:18:24 AM

Quote from: Kwajdiver on March 01, 2009, 08:14:22 AM
This is really dumb. The cover that protects the braking button, had a screw coming out. Which was preventing the button from it's full motion.
Removed the cover, and all is well.
Thanks for all the input.
Bill

At least it was an easy, inexpensive fix! Jack

buswarrior · March 01, 2009, 08:53:41 AM

Excellent!!!

I would consider putting the cover back. One more piece of insurance against unintended activation and the bus rolling away. That's why MCI started putting those on there, and there's been various methods employed to this day by both MCI and Prevost to prevent a blunt object release of the parking brakes.

Kids, animals, stuff you drop or place....

I know an in-service bus at the border inspection in Buffalo that a briefcase of a re-boarding passenger slipped down there while the driver was outside....there's a busnut whose dog put a paw on the knob....

happy coaching!
buswarrior

Kwajdiver · March 01, 2009, 12:43:16 PM

Agree,,, it should go back in place. Will get some lock-tight and reinstall. The only way I saw it, as I was sort of standing in the stairwell, when I pulled the cover up, I could see it as loose. Sitting in the driver seat, the first thing one does is lift the cover away from you, covering up the screws,,,,, sort of.

Anyway, glad it's fixed and didn't cost me any money......

Bill