MCI Air Bag Issue

[Greg Paciga (S.Ga)]

Ok gentlemen. Now the problem with the REAL motor coach. This issue started the last couple of times I've started it up after an extended dormant stage. I've had issues withe the air. It eventually clears up. But can take as long as 20 minutes. I'll break it down to what it does/does not do. And then tell you what I do to eventually get everything to work.

First let me add the bus is a MCI 9. Former N.J. Transit with the "Kneeling option" still intact. I know several people have removed the "Kneel" option from the N.J.'s. I choose to leave mine installed.

What it's doing:
The compressor works fine and pressure builds with no problem.
The  air will not FULLY raise the front of the coach. It seems that the drivers side in particular has issues. It does rise some. But not fully.
The parking brake will not engage.
The "low air" light and buzzer does not shut off.
(Here's the alarming part) the air continues to build EVEN PAST THE 120 POUND LIMIT!!

What I do to get it to eventually work:
Now I must add I don't know if one or a combination of these things eventually fix the problem but I wanted to be thourough in my description.

Once the front partially rises I let the air out of the kneel mode several times and re-air it. This may need to be done actually as many as 10 or 12 times.
I push in the park brake 30 or 40 times. I can feel and hear it eventually taking and releasing air. But it takes 15 minutes or longer.
I also press on the brake several times (mostly to keep the air pressure below the 120 lb limit since it does not shut off automatically at this point.)
Eventually the park break will SLIGHTLY engage. But no where near enough to release the brakes.
Over the course of this process. It eventually resolves it's self and all is right with the world again.

That is...until the next day. Yep..now it does it whenever the coach looses all the air out of the system.
So...any ideas guys?
Thanks for your help in advance.
Greg (S. Ga.)

[wildbob24]

Greg,

My first question would be how long since the air system was last serviced? Have you drained all the tanks? Has the dryer been serviced? Is it purging? There is so much going on here, but a lot of it could be caused by gunk and funk in the air system. These things don't like to sit and if there is excess moisture in the system, corrosion of internal valve parts becomes an issue.

The excess pressure problem sounds like the governor, but could also be stuck unloader valves in the compressor.

Bob

[Greg Paciga (S.Ga)]

Tanks are purged on a regular basis. As for an actual "service" there are no shops within a 500 mile radius (that I've found) that will work on the coach. So most work is done by me.
Thanks

[HighTechRedneck]

On the park brake, I was taught and know others that follow it that S.O.P. is to apply heavy pressure on the service brake and hold it, then push down the parking brake knob and keep the pressure on the service brake for about 10 seconds.  If that doesn't do it, another problem I've seen posted on here periodically is that the brakes can get stuck to the drums when parked for extended periods, especially in a wet or highly humid environment.

I do know a bus shop that would work on it but it is 345 miles up I-75 (Choo Choo Express Garage).  I'm sure there are closer.  You might ask Fred Hobe about a shop down there.  He is only about 30 miles from you.

[RJ]

Mike -

On the park brake, I was taught and know others that follow it that S.O.P. is to apply heavy pressure on the service brake and hold it, then push down the parking brake knob and keep the pressure on the service brake for about 10 seconds. 

Almost, but not quite - You've got it backwards.

Releasing DD3 brakes like what Greg has on his NJ MCI is done thusly:

1. Build air pressure to the governor cut-out (approx 120 - 130 pis, depending on coach).

2. Lightly rest foot on service brake pedal.

3. Push down on knob to release parking brakes.

4. AFTER pushing down on knob, apply full service brake (floor it!) and hold for 5 seconds.

5. Release service brake and coach should roll.  If not, repeat steps 1 > 4.


If you apply a full service brake before pushing down on the parking brake knob, you can set the roller locking mechanism even tighter, making it more and more difficult to release.  ALWAYS push in the knob first, before applying the brakes.


Greg -

IIRC, aren't you the fellow who told us some hilarious stories about getting your coach home after it's purchase - this being on the OLD MAK board, the one that kept crashing?  If so, welcome back!  If not, well, we're here to help!  Anyway:

First, it sounds like you might have a sticking governor on the air compressor.  Best to pull it off and head to your local HD truck parts warehouse, a replacement will cost you around $25 or so.  Standard, off-the-shelf item.  Often solves lots of problems with a new one.

Second, there might be a problem with the kneeling function.  Next time "all is right with the world", try leaving the coach in the "up" position and see if it either holds that, or comes right back up with the rest of the suspension as the air pressure builds.  Oh, and don't try to raise the front end from the kneeling position until the system is at full governor cut-out pressure - at least initially.

Make sure you're trying to release the parking brake in the manner I described above to Mike.

Setting the parking brake is also important.  You should just apply just enough service brake to keep the coach from rolling when you apply the parking brake.  Anything more and it makes it difficult to release them.

Might be easier to work thru some of this if you can use shop air rather than running the engine.  Hook it up back in the engine room so it pressurizes the whole system.

Air systems are simple, but sometimes can be quirky.  Keep us posted on what you find as you troubleshoot this.

FWIW & HTH. . .

[HighTechRedneck]

Thanks for the correction RJ.  I was indeed thinking backwards there.

[Greg Paciga (S.Ga)]

Hi RJ.
Yep..Thats me. That was a pretty good story. I have the copy of the story th Magazine published Framed and hanging in the coach. Same coach now pictured and having this new problem with.  I've looked over the answers here (much appreciated) But after 6 or 7 years with my Girl I know a new problem when she gives me one. And this is a new problem. I'm like you guys after all this time. You can just listen to her run and know there's a problem some where. I think it has something to do with a part of the Kneeling system. Just don't know what.