DD3 parking brake issues

GiddyInn · November 30, 2016, 12:57:26 PM

I have been searching but unable to find any threads describing my issue. I am new to this site and just purchased our first "big boy" bus, we have a converted school bus that has served us well for 9 years. Now we have a 1986 MCI 102a3, we have been unable to get the parking brake to release. We start the bus and let it build pressure, goes up to about 120psi, push the button in for the brakes, when we step on the service brake partailly, seems ok, but bus won't move. If we push harder on the service brake, the parking brake sets. we have a mechanic that is looking at it, but he is not familiar with DD3 brake systems. Has anyone else had any issues similar to this? I am having a hard time finding much information, or just haven't looked in the right spot yet. Thanks for any advice you may have. Brad

Gary Hatt - Publisher BCM · November 30, 2016, 01:12:06 PM

Have you tried setting the parking brake then stepping on the brake pedal then releasing the parking brake and letting up on the brake pedal? That I believe is the proper sequence for that bus.

Rick 74 MC-8 · November 30, 2016, 01:35:57 PM

I have found with my MC 8 if all the air tanks are zero pressure there is some type of Cam lobe that locks the brakes in the position they were in. after airing up pushing the button relieving the parking brakes applying full brake pedal pressure should release them. If you are saying the button pops back out during that you probably have an air leak at one of the diaphragms. If not and it's been sitting awhile could be the shoes are rusted to the drum

GiddyInn · November 30, 2016, 02:09:05 PM

Gary, I will try that. Rick, yes it has been sitting awhile, did get it to move backwards about twenty feet, but brakes wouldn't release. It would be a lot easier if it was at home instead of 40 miles away in a parking lot. Will try a couple of things next time we can make it out there.

Gary Hatt - Publisher BCM · November 30, 2016, 02:12:37 PM

If it has been sitting a while there is a good chance the drums have rusted up as Rick says. If that is the case you may have to take a 2 lb sledge hammer and pound on the drums to shock them free. Shouldn't take much though. Sometimes setting and releasing the E-brakes a few times will free them up too. I would try that if the sequence I suggested didn't work, then go pound on the break drums.

brmax · November 30, 2016, 02:15:34 PM

Maybe another opportunity to turn off engine and check for air leaks, after blocking tires.
Then possibly checking for leak down during brake application, but on a side note the quick apply for park brake release works best for me.
And if the park knob pops out like automatically then note the gauge readings, while having some good help listening.
It sure does help sometimes on these having others in mirror view listening, sometimes with the weird est signals never know to mankind.
good day
Floyd

chessie4905 · November 30, 2016, 03:17:40 PM

http://www.mcicoach.com/service-support/serinfo/serinfo04E.htm

gumpy · November 30, 2016, 03:57:12 PM

Proper release procedure is, when coach is at 120 psi, press button in, make a full application on the peddle. Don't make the application on the pedal first or you may over apply the brakes above the locking release pressure. Probably not an issue, but you should use the proper procedure.

If your button is popping back out, it has nothing to do with rusted shoes or anything other than low air pressure in the brake system, which is probably the result of a stuck valve not allowing the tank that supplies air to the drive axle brakes to air up. Suggest you take an air compressor with you, air up the bus with that, and then pull the drain valves on each of the air tanks. There should be 3 main ones and the aux tank. You could air up on the motor, and then shut it off and pull the drain valves and check for leaks in the system.

GiddyInn · November 30, 2016, 04:31:52 PM

Thanks for the advice, on a side note, is there anything electrical involved with the air brake system? Tow truck driver friend said he thought there may be a solenoid or relay that works electrically also. I forgot to mention the wiring is messed up somewhere, master switch appears to work on the dash, but the start switch doesn't work. So I have to jump it at the starter solenoid to start the bus.

gumpy · November 30, 2016, 06:31:22 PM

Quote from: GiddyInn on November 30, 2016, 04:31:52 PM
Thanks for the advice, on a side note, is there anything electrical involved with the air brake system? Tow truck driver friend said he thought there may be a solenoid or relay that works electrically also. I forgot to mention the wiring is messed up somewhere, master switch appears to work on the dash, but the start switch doesn't work. So I have to jump it at the starter solenoid to start the bus.

No. No electrical components required for braking.

Check your rear control box and make sure the front/rear switch is set to front for starting. Should be a start switch there, also.

B_K · November 30, 2016, 06:41:28 PM

OK Giddy please don't take this wrong.

But you need someone who knows MCI's to go over some things with you because it sounds like the seller didn't or you were too excited about your new purchase to listen.

Where are you located? It's possible that there is a busnut nearby you or your bus willing to meet with you and show you some things you really need to know about it.

And as Craig aka Gumpy said nothing electrical about the brakes except the brake light switch.

Also as he said there is a box in the upper left corner of the engine bay when the doors are open.
It while have a switch for front rear start, a switch that is on/off to turn off to kill the engine from the rear or to leave off when working on it to keep someone from accidentally starting it while you are in harms way working on it. And also as Craig said a momentary start switch to start from the rear also.

Let us know more about you and where your from and maybe a local nut will be willing to help!

BK

eagle19952 · November 30, 2016, 06:53:07 PM

Quote from: B_K on November 30, 2016, 06:41:28 PM

And as Craig aka Gumpy said nothing electrical about the brakes except the brake light switch.....AND THE LOW AIR WARNING

GiddyInn · November 30, 2016, 07:16:19 PM

No offense taken, I have a lot to learn, am used to gas motors and hydraulic brakes. I am aware of the switch box in the back. I was aware ahead of time that the starter switch didn't work, not sure why though. I didn't think there was any electrical components besides the brake light switch, thought I better check though, some companies do things differently, didn't want to overlook something that others might think is a common knowledge item. Thanks for all of your helpful advice, it is appreciated. I am from the Quad Cities, Moline IL area, bus is currently located in Annawan IL about 40 miles east of the Mississippi river. Just trying to expand my knowledge and figure out the most likely spots to look at so when we get back out to it we have a better ideal of what to look at and what we are looking at. No owners manual or service manual, and the gentleman that gave us the title did not know anything about it, it belonged to his son, and he doesn't live near there, so could not get any info from him.

B_K · November 30, 2016, 07:16:36 PM

Quote from: eagle19952 on November 30, 2016, 06:53:07 PM

Donald quite respectfully I have to agree to disagree with you!

I said "there is nothing electrical about the brakes except the brake light switch."

And I stand by that statement!

Yes there is a low air warning that is electrical, but that is on the AIR system not the BRAKE system.

I didn't mention it because it is in fact a different system than the brake system.

BK

luvrbus · November 30, 2016, 07:23:14 PM

If it has set for a long time the balls on the racket lock could be rusted and not releasing that will also cause the valve to pop back block it up and pump grease into the zerks on the chambers if all else fails.? does the bus have a wheel chair lift