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
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.
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
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.
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.
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
http://www.mcicoach.com/service-support/serinfo/serinfo04E.htm (http://www.mcicoach.com/service-support/serinfo/serinfo04E.htm)
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.
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.
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.
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!
;D BK ;D
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
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.
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.
;D BK ;D
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
Brad -
What you're experiencing is not uncommon for newbies to DD-3 brakes, so welcome to our world!
Craig outlined the proper release procedure above, but he left out a small, but important detail:
When applying the service brakes after pushing in the knob, push the pedal to the floor and HOLD it for 3-5 seconds, then release. At this point the bus should roll. If not, repeat. If they still don't release, you've got other issues that must be resolved.
Also, when applying the parking brake, only cover the service brake enough to keep the coach from rolling, which will allow the parking brake to function properly.
FWIW & HTH...
;)
You said the coach moved backwards?
Then the drums and shoes are not rusted seized.
If the parking control valve popped trying to release, I'd be wondering if there is stuck or blocked valving in the air system, leaving some portions with less air than the gauges indicate.
Just keep at it, air up, attempt release, see if you can get to 120 lbs on gauge, air up, attempt release.
Give the air some time to seep through whatever it is that isn't moving correctly.
That air system needs a good a proper kick in the @$# to get working again.
On the brake chamber end of things, previous owners are notorious for not giving the locking rollers in the chamber a LITTLE grease now and again.
With enough agitation, you should get it to release, however, the reliability of it all requires some serious preventive maintenance to be caught up.
The inversion valve controls everything, mounted on a bracket attached the differential, all the air lines go to and from it, tap it with some authority while the parking control valve by the driver is in the release position. Please block the wheels so you don't get run over, if fooling around under neath, suspension blocking also comes along shortly so you don't get crushed into the ground like a bug, read up about that elsewhere on here.
There are aftermarket DD3 available from.... (help me out, REM, RPM, MNR, DOT, IRS?).... much cheaper than from MCI.
My strategy is to avoid crawling and tools as much as possible, keep hammering away from the driver's seat for a LONG time...
happy coaching!
buswarrior
aftermarket new or rebuilt DD3 cannisters - http://www.rebuildersenterprises.com/ (http://www.rebuildersenterprises.com/)
DD3 parking brake 101...
On my bus, an earlier generation MCI (circa 1980) than the posters, the push-pull valve is sent air from the emergency brake tank. It sends air to the inversion valve, to tell the inversion valve to put the DD3's into drive mode or park mode. In drive mode, air is sent to the locking port to hold it open, in park mode air is removed from the locking port to allow it to lock the pushrod, and air is sent to the parking brake port to push out the push rod. When the inversion valve is told to switch back to drive mode it send air to the locking port again, letting it unlock, air is removed from the park port so the push rod is released, and the big push of air from the brake pedal pushes the push rod out a bit so the push rod sprag clutch rollers can actually unlock. So that is how that works.
The PP valve and the inversion valve work on air sourced from the emergency/parking brake tank, not the normal brake air tank. The emergency tank is separated from the rest of the bus air system by a one-way check valve, so it airs up to 120 psi and just sits there until some air is used for parking or emergency use. Air delivered to the inversion valve and used by it for it's purposes goes from the emergency tank through an 85 psi pressure regulator and then into the inversion valve. That limits the pressure that can be delivered to the parking brake port and makes sure that it doesn't apply too hard, making it difficult for the brake to release. That's why you shouldn't "set" the parking brake with an extra application of the foot pedal after you push the PP valve to apply the parking brake.
Finally - there is a spring inside the push pull valve that will automatically operate it, and apply the parking brake, when the air pressure in the emergency tank falls below a set air pressure, around 35 PSI. At that point the PP valve switches and the remaining 35 psi of air sets the parking brake. That is the fail-safe.
There is a shuttle valve that is part of the emergency braking system as well. It is connected to the treadle foot valve, and monitors the air pressure delivered from the foot valve to the brakes. It is sent air by both sides of the treadle valve (which is a two channel system), one side is fed from the normal dry tank that is the service brake air supply tank, and the other side is fed from the emergency tank (it does a lot for one tank). If there is a fault with the service brake tank and air pressure falls so that the shuttle valve senses a difference of more than around 40 PSI in the two channels (I forget the actual pressure difference and I don't have the manual to look it up), the shuttle valve decides the main service brakes have failed and "shuttles" so that the air from the emergency tank is fed directly to the parking brake port on the DD3 (through a two way check valve) so that you get several solid brake applications on the rear brakes only, through the emergency tank and the parking brakes. Once that air is exhausted down to 35 psi, the PP valve operates and the parking brakes apply using the residual air. There is no mechanical way to apply the parking brake, no big spring that sets them like spring brakes have, but the advantage of DD3 is that you get to control an emergency stop when your air supply fails.
There were several updates to this basic idea after my bus and before DD3's were abandoned, but this is a kind of sketchy overview of whats involved.
Brian
Brian, again an excellent description of the DD3 parking brakes function. I must point out though, that the push/pull valve is pulled to apply, and pushed to release the parking brakes. You might want to edit your post to correct that.
JC
Just a thought on the front start switch. On my C3 i have to have the step light on or the front start won't work. Safety or theft deterrent? who knows. HTH. Raymond
Quote from: Raymond smith on December 01, 2016, 04:42:04 PM
Just a thought on the front start switch. On my C3 i have to have the step light on or the front start won't work. Safety or theft deterrent? who knows. HTH. Raymond
Raymond -Is your coach an ex-Greyhound? The step light/starter interlock has been used by Hound for years as a theft deterrent...
FWIW & HTH...
Yes it an old hound. Good to know. Thanks for the info. Raymond
Also air is released from the "park" chamber when the dash valve is pulled out to set the park brakes (thus the whoosh sound)
Air is supplied (to overcome the parking/emergency spring) to the spring chamber when you push your dash valve in to release the parking brake.
My Prevost refused to move once like yours .Even though front and rear ap was 120 pounds .Called my bus Guru and he went through a spiel that as slow as I type would take me to Monday to tell all of it ,but the gist was to keep hitting the brake pedal to get the pressure down low enough to get the compressor working and when it aired back up ,end of problem!!!
Quote from: lostagain on December 01, 2016, 12:14:41 PM
Brian, again an excellent description of the DD3 parking brakes function. I must point out though, that the push/pull valve is pulled to apply, and pushed to release the parking brakes. You might want to edit your post to correct that.
JC
Push, pull... english is my second language... I talk fluent "forget" most of the time... I always get that wrong.
I do think that if you are going to drive a bus with DD3 brakes, let alone pretend to maintain or work on one, knowledge of the system to this level of detail in mandatory.
Brian
Here is a blurb I just extracted from the MCI website. Maybe this will also shed a bit of light on this subject.
Park Brakes - DD3 Brake Chambers
MCI coaches, with the exception of the Renaissance coach, all use DD3 brake chambers on the drive axle for the Park Brakes. When the park brakes are applied, air pressure is routed to the rear of the chamber that applies the brakes. At the front of the chamber are rolling "locks" which wedge themselves between the shaft and the body of the chamber. If the air were to leak off of the park brake diaphragm, these locks will hold the brakes in the applied position. To release these locks, you follow the steps listed below:
Start the coach and allow the air pressure to build to 120 pounds.
Release the park brakes by pressing down the park brake push/pull valve in the driver's area.
Firmly apply the Service Brakes. This causes the brake chambers to apply further than the park brakes had applied, and this releases the rolling "locks" from the shafts.
Two problems that have been encountered are listed below. Also listed will be the troubleshooting procedure for fixing it.
Park brakes will not release.
Usually having too much air pressure applying the park brakes causes this. In the air supply line for the park brakes is a pressure regulator which is set to 85 pounds. This is the amount of air pressure used to apply the park brakes, not the 120-pound system pressure. If this regulator is set too high, or the regulator has been removed, the brakes will be applied too firmly to be released by the service brake application. Setting this regulator too low will affect the stopping/holding capabilities of the park brake. 85# is the magic number to remember.
Air is leaking out of the R-14 relay valve located above the drive axle (On ABS equipped coaches, air leaks out of the modulator valve.)
In the DD3 brake chamber, the park brake diaphragm separates the park brake section and the service brake section. If this diaphragm develops a hole in it, air will leak into the service brake section. When the service brakes are not applied, this section is vented to the exhaust port on the relay valve (With ABS, the exhaust port on the modulator valve.) Any air entering the service brake chamber will be exhausted out immediately thus causing the illusion of a faulty relay valve (With ABS, the modulator valve.)
To troubleshoot this situation, remove the service brake airline from one of the DD3 brake chambers. (This is the middle hose on the chamber) If air is leaking out of the service brake port, that is the chamber with the leaking park brake diaphragm. If air is still leaking out of the relay valve and the hose in your hand, then it is the chamber on the opposite side of the axle (On coaches with ABS, air leaking out of the RH modulator valve would mean the leaking park brake diaphragm will be in the RH DD3 brake chamber, LH modulator valve would point to a leak in the LH side.)
I would like to thank everyone for all their helpful and friendly advice. We finally got Giddy Inn home!! Apparently everyone underestimated my ignorance on charter busses. I learned a lot today. After I crawled under the buss a couple of times, greased the roller locks, tapped on the valves with a hammer, and nothing working yet, called the mechanic to see if he had time to come out and check a few things. While sitting in the drivers seat waiting to hear back from him, was playing with all of the dash switches to see if they did anything. Then I saw what I thought was an ashtray lid behind the shifter, thought that was a weird place for an ashtray. Opened it up and found a black knob, looked closer to find out it said "Parking Brake" We had been trying the yellow knob on the dash near the door controls that said parking brake on it. apparently that knob is just for the storage compartment locks. Long story short, bus is home, ran great, we are more educated then we were, and have our first bus story to tell! Again thanks for everything!!
Hopefully a picture loads.
Quote from: GiddyInn on December 03, 2016, 02:35:01 PM
I would like to thank everyone for all their helpful and friendly advice. We finally got Giddy Inn home!! Apparently everyone underestimated my ignorance on charter busses. I learned a lot today. After I crawled under the buss a couple of times, greased the roller locks, tapped on the valves with a hammer, and nothing working yet, called the mechanic to see if he had time to come out and check a few things. While sitting in the drivers seat waiting to hear back from him, was playing with all of the dash switches to see if they did anything. Then I saw what I thought was an ashtray lid behind the shifter, thought that was a weird place for an ashtray. Opened it up and found a black knob, looked closer to find out it said "Parking Brake" We had been trying the yellow knob on the dash near the door controls that said parking brake on it. apparently that knob is just for the storage compartment locks. Long story short, bus is home, ran great, we are more educated then we were, and have our first bus story to tell! Again thanks for everything!!
OK Giddy first off we didn't underestimate your ignorance of charter
BUSES, but rather gave you the benefit of the doubt due to your introduction about your schoolie experiences.
Now that said I suggested you needed to be edumacated on MCI's and was hoping a busnut near you would chime in and offer up some assistance in this area. :o
Glad you have it going and sounds like someone replaced the bay door lock knob with one from a tractor trailer.
But hey look at it this way if a would be thief knows as little or less about buses than you did it is an excellent security device! ;)
Glad you got it home and now the real edumacation can now begin!
Feel free to ask away, if we don't know we'll make something up!
;D BK ;D
:o
Ok, that's funny! Someone put a brake knob on the bay doors! Cheap security, and evidently it works!
Well, now you have a heck of a story to tell regarding your first experience with your new bus. Don't feel bad or ignorant. We've all made mistakes like this. Someday when you post a question saying the bus is shutting down 3 minutes after you start it, I'll tell you about how I learned the hard way about the rear stop/run switch!
Glad you figured it out.
I could tell a story about the first time the emergency stop damper flap self-deployed and my panic as my engine would not start and would spew copious white smoke everywhere. Or about the second time a year later when I totally forgot how I fixed it the first time. Or when I left a hose off, started the bus up and when air got over 65 psi about had a heart attack as said hose started spewing very loud air (that was the day I learned my pressure protection valve actually worked).
Brian
Quote from: GiddyInn on December 03, 2016, 04:14:55 PM
Hopefully a picture loads.
NAME?? -Glad you solved your problem - the learning curve has begun!
Interesting that a PO added the "bug antennae" mirrors to your MCI in addition to the stock ones.
Oh, one other little suggestion: You've done a nice job with your forum profile, but can we request one additional item? Can you add your home/base city/state? That will help us help you with locating parts and service, plus you might discover that another busnut is nearby!
FWIW & HTH. . .
;)
I fully understand confusing the baggage bay locks with the parking brake in fact I think the are the same valve they will pop out when the pressure is low and are original equipment. Lol on my DL3 I pushed the 2 valves in for 5 minutes before I read they were for bay door locks then I found the parking brake valve under a small door by the shiftier ;D