Brake question

steve.barnett71 · June 24, 2016, 05:12:55 AM

This may be a dumb question but I will ask anyway.

The brakes on my MC9 work well and the bus stops fine. I am just surprised at the amount of effort it takes to push the brake pedal. This is my first experience with air brakes so I am not sure what to expect. How much force should it take to move the brake pedal?

bobofthenorth · June 24, 2016, 08:34:57 AM

Quote from: steve.barnett71 on June 24, 2016, 05:12:55 AM
How much force should it take to move the brake pedal?

Very little. Less than the pedal force in your daily driver. You're just moving a treadle that actuates an air valve so I'd look at the pivot point on the treadle first.

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buswarrior · June 24, 2016, 09:13:34 AM

Get under the driver's area with your grease gun.

The MCI have linkages from the pedal to the valve, which is mounted further back. each link needs lube.

Confirm the structural integrity of all mounting points, corrosion can lead to flexing, which is bad for getting the intended motion out of the other end of the linkage...

Do the accelerator linkages too, working all the way to the tunnel, and down through the floor at the other end of the tunnel. The hardest one to reach will be the one that the "hired help" didn't bother with during its commercial days...

happy coaching!
buswarrior

Gary Hatt - Publisher BCM · June 24, 2016, 11:04:36 AM

Steve, if you can't get the brakes fixed, you definitely need to get a louder horn.

And maybe even install a second horn limit switch about 3/4 of the way down the brake peddle stroke so it comes on when you are standing on the peddle.

Or better yet, get a recording of tires squealing during a long hard brake and instead of using a horn which nobody pays much attention to since all of these car alarms came out. You will also need an amplifier and a pretty good size speaker mounted just under your front bumper so when you stomp on the brakes the sound of very loud squealing tires will be heard all around. Then people will look and get out of your way.

For added affect, you could also get a smoke machine and have it blow smoke out from under the tires at the same time then everyone will know for sure it was your bus that had to make an E-Stop because some fool pulled out in front of you.

steve.barnett71 · June 24, 2016, 01:25:20 PM

I checked out the linkage and it moves freely. The resistance is definitely the force it takes to move the valve. I have attached a picture of the valve.

bigred · June 24, 2016, 02:51:57 PM

Come to Western N C Steve!! Cars up here don't come with brakes only an accelerator and horn!!

kyle4501 · June 24, 2016, 06:33:07 PM

Have you adjusted the slack adjusters? Mine took much less pedal effort once I adjusted them properly.

luvrbus · June 24, 2016, 07:42:36 PM

Could be time for a new foot valve there are o-rings and several moving cylinders inside when the aluminum housing corrodes inside they get hard to depress, thus restricting the time of air delivery and volume to the relay valves

Utahclaimjumper · June 25, 2016, 02:03:02 AM

Proper slack adjustments and SLACK ANGLES at full application make a huge difference in braking.>>>Dan

steve.barnett71 · June 25, 2016, 06:30:14 PM

The air valve needing replacement makes the most sense to me. The effort to just get the valve moving is really the same as fully applying the brakes.

eagle19952 · June 25, 2016, 09:57:01 PM

Quote from: steve.barnett71 on June 25, 2016, 06:30:14 PM
The air valve needing replacement makes the most sense to me. The effort to just get the valve moving is really the same as fully applying the brakes.

you might...run some air tool oil through it and flush our some gunk...or r+r the guts in place...then u might not have to remember which air line goes where ..

luvrbus · June 26, 2016, 06:34:26 AM

Those pedals corrode so much inside sometimes you cannot even rebuild one

brmax · June 26, 2016, 07:36:33 AM

The pivot pins or pin at the treadle itself has been the most pita for me as a truck mechanic in my career.
You mentioned linkage and the photo so I wanted to recap this more problematic area. Even though inside, everything on the shoe gets at this area and with construction and salt application vehicles it's a problem I just wanted to pass on.
A few other checks are blocking the wheels preventing vehicle movement, then releasing all the air getting to the foot valve. With this check the treadle movement and is it different than with air filled sys.
I might remove the linkage at the valve mounting area and re-check treadle and if needed lubricate and clean around the base.
I know this sounds redundant but is a costly issue that can be fixed with a regular lube/clean.

Good day there
Floyd

steve.barnett71 · June 26, 2016, 09:28:36 AM

Thanks for the replies. I will definitely clean and inspect more. The treadle did move freely when I had the pedal linkage removed but as soon as the treadle was pushed against the top of the valve it got much harder to move.

luvrbus · June 26, 2016, 09:44:02 AM

The time has come for a new foot valve I believe,if it is the foot valve causing the problem it will gradually seize and leave you on the side of the road BTDT not wanting to change it out, the spring broke inside mine and was wedged fwiw it took both feet to apply the brakes lol