MCI MC-7 question on releasing brakes "HELP"

[rdiercks]

Hi,

We have a 1971 MC-7 conversion bus that has sat in storage for about 2 years.
It's my buddy's bus and I'm trying to help him get it running.
He's starting to suffer from some memory loss and he doesn't remember some things about operating the bus.
I've got it started and running.  The Detroit 8V-71 sounds pretty good.  It's got a manual 4-speed.

When we put into 1st, or reverse, we can't get it moving.
It tries to move, but we can tell the motor might die if we let the clutch out all the way.
It's got a 4-speed manual tranny.

We've got a maintenance manual, and operator manual.
It points out a push-pull air valve, located right under the right side of the driver's seat.
We can move it up (out) and down (in) and hear air being released.
The brakes appear to remain "on" no matter what position the valve is in.

Is there some other "release valve" we don't know about?

Any clues would be appreciated.  Thanks.

Richad D.
Milwaukee, Wisconsin

[Emcemv]

The procedure is to push in the release valve and then make a hard application of the brakes with the air pressure built up to 100lbs. Then let off the brake pedal and they should release.  If it has been sitting a long time, the shoes could be rusted to the drums, you could try rocking it back and forth.

[rdiercks]

Thanks for the tips.
We'll try this out tomorrow.

Richard D

[DoubleEagle]

That year bus (at least for Eagles, anyway) would probably not have the 100 lb. release requirement. It is more likely that the brake shoes have rusted to the brake drums from condensation moisture. If gentle rocking does not free them, try banging on the edge of the shoes with a heavy hammer (5 lb.+). Also, make sure that the maxi-brake is actually releasing, otherwise you might have to screw the release rod into the spring chamber.

[luvrbus]

The bus will have DD-3 brakes build the air pressure up to 100 to 120 lbs push the PBV down and apply the brakes hard as mention they will release you may need to grease the heck out of the chambers sometimes the ball latches rust into place

[ol713]

     HI;
         Worst case, if it won't move, is to jack up the r/h drive wheels and
         remove the wheels.  Then try to release the parking brake.  Use  blocks
         and chocks for the bus.  You can then visually verify if the brakes are
         working.  If they are not releasing,  then you have access to remove
         the DD-3 can for rebuilding.   That is what I had to do with  my
         MC-7 just last Dec.
         If your coach has set for a couple of years, you can also see if the
         air bags are filling up.  I would use shop air instead of running the motor.
         Let us know what you find.
                                   
                                                          Good luck,     Merle.

[rdiercks]

Hey everybody, thanks for the tips.  I'll let you what happens today, when I try to get the parking brake to release.
One other thing that has begun to puzzle me.
What the heck is the correct air pressure for the tires?
After sitting a couple years, they look a bit "low".
I've searched through the maintenance manual and the owners manual, not a single reference to tire pressure.
Any idea of where that info is hidden?

Richard D

[Dave5Cs]

Look up the tire pressure to weight chart for the type and size of tires on the bus. There might be a tire plaque affixed somewhere in the bus or in the engine compartment that will get you close. If not weigh the bus at a commercial scale and then compare to the chart. My chart says between 90 and 100 lbs for my 11Rx22.5 tires. my 5C weights 28,000lbs roughly. fron t axle 7800lbs and the rest in the rear. HTH
Dave5Cs

[rdiercks]

Hi Dave,

Thanks for the tip.  I'll hunt down that info and see where it leads me.

Richard D

[rdiercks]

Got the baby off the parking brake and moving forward/reverse.
Thanks for the info.
Regarding tire pressure;
to help with calculating tire pressure;
anyone have an idea of what the general weight of our MC-7 is?
We're thinking it may be close to the original weight, given that all the original seats are gone, and only some cabinets, a counter, a refrigerator, a bed, and a bathroom have been added.
Any thoughts?

Richard D

[Emcemv]

I run 100lbs in mine. I don't think you can go wrong with that, sometimes you can run less depending on your weight to get a better ride..

Bruce

[luvrbus]

100 lbs in all tires and go it has been siting for 2 years they are going to have flat spots to round out anyway

[RJ]

Richard -

As Clifford mentioned, your MC-7 has DD3 brake cans on the drive axle, and his explanation of how to release them is right on.  Just make sure you push in the parking brake knob first before you apply the hard service brake application.  Also, holding that application for 3-5 seconds gives the locking mechanism time to release properly.

Here's a tip for setting the parking brake that can potentially save you some grief down the road:  When you come to a stop, and it's time to set the parking brake, apply the service brakes just barely enough to keep the coach from rolling, then pull the knob to set the brake.  Release the service brakes and you're done.   By using this very light service brake application, it allows the locking mechanism inside the DD3 cans to be released more readily when you do the hard service brake application.

Regarding tire pressure, Clifford's suggestion of putting 100 psi in all eight as an initial starting point is fine.  However, like Dave5C mentioned, the only correct way to properly adjust the air pressure requires you to know how much weight is being carried on each axle.  Most major truck stops have a CAT scale that will accurately weigh your coach - well worth the 10 bucks or so.  Make sure you're in "ready-to-roll" trim, with full fuel and freshwater tanks, plus clothes, groceries, etc. when you hit the scales to obtain the best readings.  After that, refer to the tire manufacturer's "loaded inflation table" for the size tires you're running to find their recommendation for the weight the tires are carrying.  If your numbers fall between recommendations, use the higher pressure.

Just a little more complex than 35 psi all around in your car, eh?

Welcome to the madness!!

FWIW & HTH. . .

[rdiercks]

RJ,

Thanks for those detailed tips on the parking brake and the setting of tire pressures.
Appreciate it.

This forum has been a "savior" me.

Richard