Can anyone tell me about a kneeling bus. Our church bus is now lower at the front passenger door for some reason. It never has before. Luke told me it my be in a kneeling feature that we didn't know it had. Someone could have flip a switch somewhere by accident. It's a 1981 MC9 bus. Any help out be great. Thanks
MC9s didn't have a kneeling feature. I would look at the ride height valve. Maybe the linkage for it just came undone.
79 and 80 4905's had kneeling as an option.
Anyone know what this part is?
It is under the bus up by the steps
Quote from: fairbus on September 09, 2022, 04:58:03 PM
It is under the bus up by the steps
Aw given it's not attached to the suspension maybe it was a step extender?
Your picture, perhaps a remote tank drain? Where does the attached cable to the bottom go?
As noted, no kneeler in an '81 MC9, look for some corruption of the levelling valve.
Happy coaching!
Buswarrior
As noted by others we found no kneeling switch on bus. The picture of the part is actually upside down. We hopefully plan on tracing down where that line goes to tonight. The leveling valve is just a few years old and the drivers side seems to come up fine just not the passenger side and the passenger side air bags are also only a few years old. Going to trace that line and spray some soapy water on and around passenger air bags to see if we find any leaks other than that part. Thanks for replies.
Quote from: fairbus on September 12, 2022, 05:41:51 AM
. . . the drivers side seems to come up fine just not the passenger side. . .
Fairbus -What you're describing is a classic symptom of the passenger side leveling valve on the rear axle acting up. It's stuck, binding, or the linkage has come loose.
FWIW & HTH. . . ;)
RJ
So the rear leveling valve can effect the front and put it in a bind that it won't lift. Now just a fyi we did do a test where we disconnected both the rear leveling valve arms so the rear would not lift to see if it was getting in a bind and we had the same result in that the front passenger would not lift but about 1".
That points to a problem with the air bag or the air supply to it.
That points to a problem with the air bag or the air supply to it.
You'll note that many of us include our location in our signatures. Often, it's discovered that another member is close by and can take a look. So, where are you?
Arthur
Sorry we are in Duncan, OK
Let me start from the beginning when this all started. Our church has a 1981 MCI MC9 bus. When we first installed our new rolling lobe bellows on the rear drivers side(because the air rail had a leak and it was leaning to the drivers side at the back) the front passenger side doesn't seem to air up (which did just fine before we replaced that rear divers side).The drivers side front does which seems strange since they work off the same leveling valve. We thought maybe with the new driver rear bag aired up so high now that maybe it was putting a lot of pressure on the front so we put the passenger side rear rolling lobe bellow on and it didn't help any. We started out with the rear driver side leaning down. Now the front passenger side leans down the most. It seems strange that all was fine with the front until we change the back with the new bags. Any help is greatly apricated. We are going out tonight to see if we can find anyone air leaks besides the on in the pictured above part that even MCI doesn't know what it is and it has MCI on the side of the part. But what still seems strange to me is that all the front was fine until we put that new air bag on the back.
Fairbus
Duncan, OK
one levelling valve controls all 4 front airbags. Which means they should be same height on both sides. For front to tilt, one side or other, one of the two rear valves being mis adjusted or bad. left rear too high, right front will be lower. right rear too high, left front lower or vise versa. (When running) or aired up If this only happens after sitting a while, could be a leak at front or rear. They only use one levelling valve on the front to avoid a situation where body could be twister by leaning different front to rear. check clearance at bump stops on rear on both sides. they should be within about 3/8 to 1/2". Remember to do anything underneath safely with proper blocking.
Side to side is controlled from the rear. Full stop.
Hike up one side at the rear, as you did by changing to a different air spring, and the opposite front goes down.
No symmetry at the back, the front cannot get level.
Fix your rear ride heights to stock, and watch the bus level out.
Self inflicted wounds.
happy coaching!
buswarrior
So is there a standard that the height should be at the back? The drivers side new rear rolling lobe air bags inflates more than the passenger side. Is there a standard tire clearance from top of tire to wheel well? I know the rear drivers side leveling valve was changed but not a MCI one and he said it was not adjustable. I may need to get a MCI one I heard they were adjustable. We think the passenger side rear one is a MCI because the guy going under the bus said it did look adjustable. The single front passenger leveling valve is not a MCI either and is non adjustable. We did last night take the front one loose and moved the handle to make to put more air in the front bags but the passenger side would never catch up to the drivers side. Which is going along with what is being said about the rear leveling affecting the front leveling. We soaped everything down last night and found no air leaks up front.
The part we send a picture of seems to be the left overs of what someone on here said was a extra step that came out from under bus. After looking there seemed to be some bracket that might have supported the extra step. When we get some air plugs we are going to take that part out.
Thanks for any help on what the standard heights and clearances should be.
Ronnie
Fairbus
Duncan, OK
You should have matching bags on either side of same axle.
Ride height control valves are not adjustable. You adjust the height with the linkage/rod. Some are adjustable, some you bend until you achieve the desired height. I don't know the height specs, but you should have as straight a line as possible for the drive shaft to minimize wear and tear on the U joints.
Some valves have a longer delay than others. You should have matching valves from side to side.
The front bags are manifolded together. The side to side height is dependent on the rear axle.
You need a service manual for your bus.
There should be a specification in inches between tip of stock bump stop. ( rubber boob looking thing )
Sometimes they are missing or deteoriated. Luke should I understand have them. If not able, adjust leveling valve link.
Ronnie -
Get a bubble level from a local RV store's accessory department, and dig a tape measure out of your toolbox.
IIRC, with the bus sitting level per the bubble, on an MC-9, the top of the bottom step should be between 14" and 15" off the ground.
This, of course, is after you get the rear leveling valve situation figured out.
FWIW & HTH. . . ;)
RJ
I don't remember the actual measurement location or measurements on the MC9, but a quick call to MCI Tech Support will get you all the info you need.
I'm pretty sure once you get the rear set right it will all be ok.
But you can do a quick check of that right front air bag by disconnecting the air line going in and seeing if it has sufficient air coming out of it. If not there is a blockage somewhere. If it does then you have an air leak in the bag or mounting area! I don't remember if the front used an air chamber (the reason you had to put rolling lobes on the rear!) like the rear or not.
;D BK ;D
Thanks for all the great advice. Listening to all of it. Please keep sending advice my way.
Got from Luke a new set of MCI leveling valves for all 3 places. I really don't see how they are adjustable. Are they adjustable or are the rods bolted to them adjustable somehow? Hope to get them installed soon. Looking forward to getting this bus back on the road for our church.
Thanks
Ronnie
Fairbus
Duncan, OK
you can kink the rod or on mine the rod is slotted where it connects to the larger pivot, and allows adjustment by loosening the small screws and moving the link arm one way or the other a little.
Got all three new leveling valves on. Seems to be a lot better. At what point is best to set valves? At a full 120 pounds of pressure? The height seems to keep changing on us. Also is there a locking gas cap for a MCI 9?
People usually just add a lock on the access door. Dedicated thieves wont be deterred by locking cap.
You should end up with 3-1/4" between the bump-stop and the pad at correct height. :^
I have a question for you guys that know this system well.
I want to purge the rear airbags for leveling. (102DL3) On the front it's easy as there is a purge valve that I can trigger, it was used for the "kneel" function. I think I can probably assume that doesn't exist at the rear. There are probably several ways this can be done so I'd like to hear some suggestions. What do you think would work well?
The reason is that I have leveling jacks and want to drop the carriage to the bump stops before jacking so that the step into the bus is as short as is practical.
Jim
No "rear raise" on that coach?
Valving for that settles the rear back to ride height not as fast as the kneeler, but fast enough for what you want.
Happy coaching!
Buswarrior
Thanks BW, it does have rear raise but operating that switch doesn't settle the rear down onto the bump stops. I want to drop it all the way down. Do you think there would be a way to do that with the rear raise/lower components?
In front the Kneel switch does that by energizing the Purge solenoid valve and venting the pressure from the airbags. Looks like there is a reference pressure involved in that too and I've forgotten exactly what that does, but I think it sets the minimum pressure in the bags at kneel. I'm looking for a way to do something similar at the rear.
It looks to me like the raise/lower might operate by changing a reference pressure for the system but I'm still learning how that works. I wonder if dropping that reference pressure to near zero would cause it to settle down onto the stops. I dunno, maybe the leveling valves would prevent that.
Jim