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Author Topic: MCI 8 air problem  (Read 2525 times)
buylow8
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« on: February 14, 2012, 09:24:14 PM »

I have a 76 mci8. my problem is my air bags and emerg brake sw will not work. my low air light never goes out, the air gauge keeps going up past 130, if i step on the brakes the pressure reduces with each push. Does any one have an idea and a air system drawing?
kurt
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buswarrior
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« Reply #1 on: February 15, 2012, 12:06:46 AM »

I anticipate you may have more than one problem happening at the same time.

The low air switch, attached to the side of the rear electrical junction panel might be sticking/is broken/needs adjusting. It has an airline leading to it.

Is it below freezing where you are? You may have frozen water moisture disabling the proper function of your air system.

We need your unit number off the builder plate, to choose the correct schematic.

The MC8 are the most complicated of them all, there are 8 different schematics in my book for a 6 year model run 1973 to 1979.

Operators are waiting to take your call...

happy coaching!
buswarrior

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« Reply #2 on: February 15, 2012, 03:34:23 AM »

"Operators are waiting to take your call...

happy coaching!
buswarrior"

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bevans6
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« Reply #3 on: February 15, 2012, 05:52:46 AM »

"Operator, Operator, make me a call..."

It strikes me that if the suspension isn't filling, the low air warning isn't going off, the governor pressure sensing line isn't switching the compressor off, the brakes work but the emerge brake switch doesn't, and the air pressure gauge works - a common point is the check valve and line coming out of the dry tank.  They all tee off that line either just before or just after the E-filter and the pressure protection valve.

Edit - on my MCI the governor pressure sense line, the rear low air switch, and all of the accessories in the engine compartment are all fed off of one line that tee's from just after the pressure protection valve.  The suspension tees off there as well, and the emergency brake tank is fed from there too.



Brian
« Last Edit: February 15, 2012, 06:42:39 AM by bevans6 » Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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1972 NTM MK-4 B/SR
RickB
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« Reply #4 on: February 15, 2012, 06:27:05 AM »

I can't speak to the other issues you are experiencing but the gauge should lose a bit of pressure every time you engage the brakes as you are releasing air to apply the brakes. The cutout point for your governor is easily adjustable with a set screw on the top of it. Although I can't remember what the factory cutout pressure is I seem to remember somewhere between 115 and 125 lbs. Can you hear a leak when the bus is running? if not,  do you have an access point to your system to hook up a compressor? If you are in an area cold enough to hard freeze you may need to idle the bus for quite awhile during the warmest part of the day to get it to thaw and I'm sure some here know how to add alcohol to your air system to thaw it.

Hope you get it figured out.

RB
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robertglines1
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« Reply #5 on: February 15, 2012, 06:37:12 AM »

Need more info: see your new to board.  need location so we know your general weather. and bus nut maybe close by.  been there in you problem. so need a little more info.   might be as simple as getting all the air pressure to bleed out of system by shutting engine off or letting engine run to heat up engine compartment.or placing heater inside compartment driverside  outside lower compartment where overrule/acessorie tank is.  does engine shut off work? reason for asking dumb question.  Bob
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buylow8
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« Reply #6 on: February 15, 2012, 08:29:00 AM »

The bus is located just north of Little Rock. I think Brian is on the right track. i also think one part is causing the problems. I let the bus idle for atleast 30 min yesterday and sun. sun was cold so i thought it might be somethig frozen, so i went out yesterday at the end of the day and it still had the problem. I will go back today and get the unit #.
one more thing, i have a gauge on the back of the compressor and it read 0 psi
kurt
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buylow8
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« Reply #7 on: February 15, 2012, 08:36:42 AM »

Bob
i have never been able to shut off the bus from up front in the 5 years i have had it. i have to put the sw upfront to off then go to the back and turn a lever on the engine behind the belt to get it to stop. the emerg protected shut off sw upfront doesnt work either
kurt
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bevans6
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« Reply #8 on: February 15, 2012, 08:57:18 AM »

I would start by draining the wet tank and the dry tank to zero and see what comes out.  The dry tank is behind the wall of the drivers side rear luggage bay, you get at the valve by lifting up a little access door immediately on the right with the bay door open.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
thomasinnv
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« Reply #9 on: February 15, 2012, 11:32:17 AM »

stuck pressure protection valve.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
buylow8
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« Reply #10 on: February 15, 2012, 07:45:40 PM »

ok i got the #'s

unit # T57-579
ser # 1590
sept 1976
kurt
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buylow8
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« Reply #11 on: February 17, 2012, 09:51:52 AM »

Thomas
thanks for the air system drawings. All of them are very similar to each other. I think your right, the pressure protection valve is stuck or even the filter before it is clogged. would you have a part # for them?
Also does anyone know where the low press light gets it info from. Where does the press gauge get its info from? The drawings dont show this info.
Kurt
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bevans6
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« Reply #12 on: February 17, 2012, 09:58:46 AM »

On my similar vintage MCI the pressure gauge reads from the dry tank, and the low pressure light reads from accessory system. actually the same line that feeds the governor sense port and the accessories in the engine bay.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
buswarrior
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« Reply #13 on: February 17, 2012, 02:15:17 PM »

great news, you're getting there!

That's a TMC coach, not an MCI, the unit numbers are a different scheme.

You need to be very watchful as to which way your coach is plumbed, depending on the job you are trying to do. There were big changes in the 1975/76 years, which were then reversed, and then somewhat reinstated, over the course of approximately 2 years. Air gauge plumbing is one of the things that wandered around, back and forth between accessory and service tanks

The confusion has only gotten worse as the years pass, not better, as various owners have changed things.

Maybe I drew it up once and posted the points of division by MCI unit number? Manual is hiding at the moment.

The low air switch is a "Penn Air" switch, housed in a metal box attached to the rear electrical junction box, all the way around the corner from where you look in. It served multiple purposes, show the low air light to the driver, and engage the alternator and coach HVAC once sufficient air pressure was present for a belt drive alternator to not throw the belts on loading.  It is adjustable and like all moving things that are old, sticks with disuse. There will be a small airline going to it, from a junction block on that side of the engine, if all that hasn't been stripped out by a previous owner.

happy coaching!
buswarrior



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buylow8
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« Reply #14 on: February 17, 2012, 08:48:33 PM »

I am going to look under and around the bus and see if i can find that bad part in the morning. Why couldnt they build the bus so it sits more than 3" off the ground when the air bags are flat. guess i will bring my shovel and dig a trench under it.
kurt
Also, this bus has the 2 tanks above the front axle. and i assume there is no access panel from the top?
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thomasinnv
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« Reply #15 on: February 17, 2012, 10:38:17 PM »

the only access to those front tanks is by crawling under the bus. be careful, busnuts have been squashed to death.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
buswarrior
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« Reply #16 on: February 18, 2012, 12:22:38 AM »

You don't need a shovel to find the rear electric junction box, just open the driver's side engine access door, the one on the side, not the rear. The junction box is mounted right there on the wall, to your left, inside the fender for the tag wheel.

If the temps are below freezing, you might want to just wait?

There are too many variables for trouble shooting for throwing frozen moisture in any random place into the mix.

I really, really hate wasting time working on something that doesn't need working on, due to bad diagnosis.

Some call me lazy, some call me smart...

happy coaching!
buswarrior

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bevans6
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« Reply #17 on: February 18, 2012, 04:00:43 AM »

There are four tanks on your bus.  The dry tank is behind the rear wall of the rear luggage bay on the driver's side, and the drain valve is through a small door at the foot of the wall just inside the luggage bay door.  The two tanks in the front axle bay are the emergency tank and the wet tank.  The wet tank is on the drivers side and the emergency tank is on the passenger side.  The pressure protection valve and the E-filter are mounted on the emergency tank.  There are normally pull type drain valves that you can attach a chain or cable to, or hook with a long stick with a bent end.  The last tank is the accessory tank, it's up front under the driver's seat in the compartment there.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
buylow8
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« Reply #18 on: February 18, 2012, 01:11:17 PM »

Thomas or anyone else
Do you have the drawings for the airbags?
kurt
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buswarrior
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« Reply #19 on: February 18, 2012, 01:51:33 PM »

What drawings did you get from Thomas?

All that stuff you've mentioned in the thread is on the stock drawings.

Pretty rare for that E filter to get clogged.

Also, pressure protection valves tend to fail by letting the air through early, as the spring ages or breaks, not block it up completely.

As Brian suggests, is there air present in all the tanks, and drain them, and see what the recovery might be?

I'm thinking blockage, as opposed to failure.

happy coaching!
buswarrior

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buylow8
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« Reply #20 on: February 18, 2012, 02:08:24 PM »

Thomas gave me an air brake system drawing. i hope it warms up a bit more so my problem goes away on its own
kurt
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thomasinnv
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« Reply #21 on: February 18, 2012, 09:55:33 PM »

I just emailed you the suspension air schematics. I didn't even notice they weren't part of the schematics i sent you already.

BW, the pressure protection valve absolutely can fail in the described manner, and not just by opening too low. I had the same exact problem as the op describes a few months ago due to a sticky ppv. My air would go over 100 before the ppv opened. can be common in colder climates.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
buswarrior
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« Reply #22 on: February 19, 2012, 11:19:33 AM »

Crack open the lines leading to the ppv and give it a shot of your favorite air tool oil.

Be prepared to do a little re-adjust once it is freed up, but after it has been cycled a few times. let it settle in to its new found freedom.

My use of words may have led us astray?

Sticking is a blockage, which can be remedied,
failure requires the replacement of the component due to it being unable to perform as intended in a permanent manner.

Many apologies!

happy coaching!
buswarrior
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buylow8
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« Reply #23 on: February 22, 2012, 06:14:24 PM »

Thomas
thanks for the air suspention drawings.

I ran the bus again when the temp went into the high 50s and its still not working. I had a truck mechanic stop by and he hooked up his air compressor to the emerg fill air valve and was able to release the emerg brakes. i am going to drive it to his shop a mile down the road and have him fix it. i will post what the fix was
kurt
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buswarrior
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« Reply #24 on: February 22, 2012, 06:17:48 PM »

good news! you'd like for your mechanic to explain to you what he has done, what diagnosis he did, what he found right, and what he found wrong, and what he did to fix it.

Not so much for us, but for your own growing knowledge of how the beast functions.

If you learn as you go along, he gets more business, if you don't learn anything....

happy coaching!
buswarrior
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Scott Bennett
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« Reply #25 on: February 22, 2012, 06:44:19 PM »

Kurt Just a side note on your engine stop lever. You said you have to manually kill it by pulling that lever. Is it stiff when you pull it? If so, it's merely not returning via spring to it's off position. You merely need to unseize the lever from it's likely seized washers down near its base. Fixed my problem. Much safer than reaching in there every time.
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Scott & Heather
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buylow8
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« Reply #26 on: February 22, 2012, 06:55:07 PM »

scott
the lever is not easy or hard to turn. it looks like there is an actuator that should push the lever but it looks like it or the lever was moved out of the way. i guess the guy before me had a problem with it and moved it. i never fixed it because it is about # 10,000 on my things to do list
kurt
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thomasinnv
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« Reply #27 on: February 22, 2012, 07:27:25 PM »

the spring is not what activates/operates the engine stop lever, the air cylinder operates it. If it was moved to the side by the PO then chances are that once the air is up in the system you will find the air cylinder to be energized. you most likely have a faulty air valve, engine stop switch, or faulty wiring between the two. For those that don't know, MCI uses a remote air valve mounted on the rear bulkhead, which activates the air shutoff cylinder on the governor.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
Scott Bennett
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« Reply #28 on: February 23, 2012, 04:56:06 PM »

scott
the lever is not easy or hard to turn. it looks like there is an actuator that should push the lever but it looks like it or the lever was moved out of the way. i guess the guy before me had a problem with it and moved it. i never fixed it because it is about # 10,000 on my things to do list
kurt

Oh ok...different problem than mine was.
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Scott & Heather
1984 MCI9 6V92-turbo with 9 inch roof raise & conversion in progress.
http://www.scottmichaelbennett.com/p/our-bus.html
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