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Author Topic: 87 MCI MC-9 Allison HT 748 4 Speed Auto Trans issue  (Read 5069 times)
thepiratebus
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« on: May 22, 2011, 06:03:11 AM »

Any help would be greatly appreciated.  Last winter we hit something leaving a parking lot that pierced our tranny pan.  Luckily we immediately shut down, but it did run us dry on fluid.  We had the unit towed to where we work on the bus (removing the axle to avoid any more issues).

We were able to weld the pan and so far no leaks.  We put the pan back on, refilled to proper level and it would not go in gear (any gear).  Could cycle through all gears on the auto shifter.  We drained it again and removed the pan only to realize that the filter/screen was bent and not sitting correctly.  A solenoid (closest to the front) was also loose.  We reseated the solenoid and put a new screen in that we got from the Allison dealer.  While it now would now go in gear occasionally it still is random.

We parked it for the winter and tried to get it out this spring.  Fluid levels seem OK (although instead of the level rising when hot it went down) so we added a little more, careful not to overfill.  It randomly goes in (more often in Reverse), but still is not right.  When it is in gear, it seems to go fine.  Once going down the highway 2-4 gears work perfect.  Odd part is it seems to go into gear when we cycle through the shifter and play with the parking brake.  This could be just random luck too (wishful mojo).  My thinking is it is the solenoid that was loose.

Questions: Could this be it?  Other suggestions?  Is there a way to order just that one solenoid?  Any help would be appreciated.  Don't want to have the tranny guys have to make a house call.  Thanks in advance.
« Last Edit: May 22, 2011, 06:35:55 AM by thepiratebus » Logged
luvrbus
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« Reply #1 on: May 22, 2011, 06:21:32 AM »

Doesn't sound like a 740 to me are you sure about the model ? maybe a 741 or 748 electronic a 740 has no electronics in the pan 

good luck
« Last Edit: May 22, 2011, 06:29:29 AM by luvrbus » Logged

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Chopper Scott
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« Reply #2 on: May 22, 2011, 06:24:51 AM »

Electric shifter? My 740 has a manual type lever.
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thepiratebus
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« Reply #3 on: May 22, 2011, 06:32:54 AM »

Sorry - this should be the 748 for the auto.
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luvrbus
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« Reply #4 on: May 22, 2011, 06:47:31 AM »

My condolences to you guy but more than likely a bad solenoid or bad ground you need a guy with a reader or laptop to check it for you it will be money well spent unless you have plenty of time on your hands.
Buy some electronic cleaner and clean every connection going to and from the transmission maybe just corrosion on the plugs after cleaning use a good electronic grease on the plugs then go from there  


good luck
« Last Edit: May 22, 2011, 06:58:32 AM by luvrbus » Logged

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NeoplanAN440
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« Reply #5 on: May 22, 2011, 07:14:38 AM »

try reading the transmission codes first!
there should be a test switch near the dash. hold it , with the engine running in idle, transmission in N and park brake engaged.
code will be shown by a a transmission test light. counting how often it flashes.
like the old obd one systems.

the ht 748 is very sensitive to wiring problems or bad connectors.
maybe a cracked connector plate on the valve body (from hitting by the pan)

mine gave me a thousand issues, due to a bad pan connector, that had insulation issues between the locking tabs!
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thepiratebus
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« Reply #6 on: May 22, 2011, 07:19:48 AM »

Thanks guys!  Is there a code index to match the flashes to?
« Last Edit: May 22, 2011, 07:39:12 AM by thepiratebus » Logged
luvrbus
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« Reply #7 on: May 22, 2011, 07:35:40 AM »

That transmission fluid is checked hot while running make sure it is full hot not cold and not running should have taken around 7+ gals to refill depending on the pan

good luck
« Last Edit: May 22, 2011, 07:37:53 AM by luvrbus » Logged

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buswarrior
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« Reply #8 on: May 22, 2011, 07:58:50 AM »

Perhaps a coincidence, how old is your filter?

Proper functioning is dependent on fluid level and flow.

happy coaching!
buswarrior
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thepiratebus
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« Reply #9 on: May 22, 2011, 08:10:28 AM »

Good question - probably need to check that at the same time we are under there.
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trailblazer2
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« Reply #10 on: May 22, 2011, 09:53:42 AM »

I have the exact same type of coach ,as you!I would read the codes off of the lights (located in the back baggage bin,drivers side)This will tell a lot.The conectors are sensitive & might be loose? However start with the tale tale light in that back bin. I might have a translation book,just let me know.
 Bill
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« Reply #11 on: May 22, 2011, 12:15:12 PM »

if you read any  codes, i can tell you the problem and troubleshooting guides by the manual that i have.

if no code is stored, there will be no flash

check if the light will come on for 3 sec when you turn the master switch on.

as soon as you select r   it will erase any codes!!!
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NJT5047
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« Reply #12 on: May 22, 2011, 08:17:46 PM »

Your coach probably has an electronic high idle and kneeling system.  It might also have a lockout switch that prevents shifting when the door is open.  
If the red indicator lights work when you push the touch pad, the shift pad is probably working.
If this problem began when the oil pan was damaged...probably something related to the repair...or the big trans electrical connector on the PAX side of the trans housing.   If the problem existed before the trans pan was holed, some sort of electrical problem exists.  
As Bill said, most '87 DDEC 1s have code reading capability in the upper drivers side rear bay.  There are two lights on a panel.  The green light is the ATEC reader (red light reads the DDEC ECM).  The lights might still have the factory cover over them which can be openedd with two zeus buttons.   The engine doesn't have to be running to read codes.   Turn on the battery disconnect, turn on the ignition master, and go to the LH rear bay and hold the switch next to the green light and count the flashes.   It will flash on set, pause, and flash the second digit.  
Other signs of electrical problems outside the trans are no "Check Transmission Light" in the dash for about 3 seconds whenever the master ignition is turned on, and "Do Not Shift" indicator on the touch pad...or no pad indicator lights.
There are ATEC fuses in the battery box that are famous for corroding.  They should be checked.   Once the fuses are pulled, any codes will be erased.  DDEC II and up will store codes, but DDEC 1 requires B+ in order to store codes.  
Unlikely that you damaged the trans due to idling once the trans fluid leaked out.   Once air hits the hydraulics it won't go, yet the trans is still lubricated.  For a short period of time.  
If any other work has been done on the coach that preceeded you trans problem, consider what might have been moved or dinked with.  
There's a large multi pin connector on the bottom of the touch pad. The'll get loose and cause problems, and the touch pads will eventually fail.  
Take a look as all of your CELs, touch pad lighting, and DNS light and see that they are functioning.  The ATEC harness is one piece (originally anyway) back to the ATEC.  There are connections at the front and in the rear bay.  
BTW, if you have codes set, post what you read and I can ID the code (s) for you.
Good luck, JR  
« Last Edit: May 22, 2011, 08:20:37 PM by NJT5047 » Logged

JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
thepiratebus
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« Reply #13 on: May 23, 2011, 09:31:22 AM »

Thanks - I will get in there this week and see what is going on with the light.  The shifter lights up and the bus in fact will go in gear 1 out of every 6 times.  Reverse, when it goes in, actually works as normal.  When drive kicks in it usually has very little power (like stuck in first), however last time we were bold enough to take on the highway after our pan fix and screen install it hesitated in first, but 2-4 worked fine both up and down shifting.  Check engine light does come on occasionally (not every time) when you put in drive.  It did not do this before the pan incident.

Thanks for all the help and we will see what comes out of those codes.
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NJT5047
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« Reply #14 on: May 23, 2011, 10:22:39 AM »

The transmission should drop firmly into drive and stay there.  Shouldn't "slip" or jump...however, unless you are familiar with large equipment transmissions, the feel may seem abnormal when it isn't. 
Another thing is that the park brake may not be releasing completely and it would seem as though the coach wouldn't pull when in gear.   If the park brake releases, the coach will usually move slightly forward (if on flat ground) when "D" is selected.   If it doesn't....recheck the park brake.  Even with the park brake applied, you'll feel the transmission engage when "D" is selected.  If you don't feel the "engagement," then the transmission system has an issue. 
An '87 MC9 DDEC1 is slow on takeoff.  The transmission will 'hesitate' or 'hunt' when shifting if you slack up on the throttle or use a light touch on the throttle.   First gear just rolls off slowly.   
The best way to drive the bus is with the throttle almost on the floor when you want to accelerate, and off when you want to slow down.   The transmission will 'hunt' around if you lighten up and then slightly accel.   It'll shift into 4th lock at something close to 35MPH on a light throttle, and then if you speed up, it'll downshift 2 or 3 gears down as it looks for the best map.   
Often if you want to cruise along at 35 MPH or so, selecting "3rd" gear will work great.  Forcing 3rd will keep the trans from hunting back and forth between 4th and 3rd. 

HTH, JR
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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
thepiratebus
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« Reply #15 on: May 23, 2011, 04:20:12 PM »

OK - latest update.  My buddy who has it at his house right now opened up the compartment and stated there were two red led lights one on top of the other as well as two toggle switches (with red covers) to the left of the lights.  Which one of the toggles should we try or more importantly trust for the code.  He said to the right of the lights were a bunch of relays and such and then two black boxes with Allison transmission on them.

Thanks - at least we feel we are heading in the right direction now.
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NJT5047
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« Reply #16 on: May 23, 2011, 07:52:02 PM »

One of the lights should be green.  PO probably changed out the ATEC light.   I'll go check tomorrow and let you know which light is the ATEC. 
There's an easy way to sort it out, hold either switch and count the flashes.  If you flash out a  "25," that indicates no codes on the DDEC ECM (there may be stored codes in the DDEC which would complicate this process).  So the other switch is the ATEC.   
Both the ATEC and DDEC ECMs are mounted to the right of the switch panel.  I'd advise to avoid manipulating the wiring around the ECMs.   The wiring might be in excellent condition, and it may not. 
If you see signs of water damage, or any corrosion in the compartment, the ECM plugs might have corrosion and become intermittant.   Then you'll have to carefully pull each and check.  99% of problems with DDEC electronics are due to corrosion or POs chopping up wiring. 
JR
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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
thepiratebus
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« Reply #17 on: May 23, 2011, 09:20:16 PM »

Thanks - we'll start looking this week at all the connections too.
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NJT5047
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« Reply #18 on: May 24, 2011, 04:20:09 PM »


Checked the location of the code lights on my NJT MC9 today.  The  ATEC is the bottom light and bomber switch.  And it is green on my coach.   
I've seen some coaches that have had all, or some, of the code switches altered or removed.   POs do some interesting things with DDEC/ATEC wiring.   The electronics are like black magic when things start to fail.     
If the code readers don't work, they are simple to get going again.   

HTH, JR
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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
thepiratebus
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« Reply #19 on: May 25, 2011, 09:45:04 AM »

Thanks - going to try and check it all out before weekend.  Appreciate everyone's help - frustrating problem.
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luvrbus
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« Reply #20 on: May 25, 2011, 09:52:12 AM »

Comes with the territory of owning a 700 series electronic transmission once you get it straighten out it may last for 10 years or 10 minutes with out problems you never know

good luck
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thepiratebus
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« Reply #21 on: May 25, 2011, 05:39:38 PM »

The codes are in.  Hopefully someone can give us a hint as to what this means.  Called my buddy and he fired it up this afternoon.  He said the bottom led was green once he started it, so that corrects that confusion.

He let it idle for a bit to build pressure and heat up.  Once warm he left it in neutral with the brake on.  He went and did the bottom switch and the green light flashed once, pause, then 4 times.  It repeated this pattern.  He then wanted to see what the top one did, so he did that and it flashed quickly 10-12 times.  He then did the bottom one again and it did 6, pause, 6.  He put it in gear (did not really move) and then he put in neutral and has repeated since (without shutting off) and it continued to do 6,pause, 6.

Personally I think the 1, pause, 4 was the correct code and the other was due to the other switch, but we might try again after it shuts down and starts back up.

Thanks
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NJT5047
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« Reply #22 on: May 25, 2011, 07:17:49 PM »

The ATEC code "14" is "Forward Pressure Switch" fault.   Sorry, but I'm not familiar with the internals in the transmission...so cannot advise what exactly we're talking about, however, almost all of the electronics in an ATEC transmission is serviceable without pulling the trans.  This is good.
Another caveat:  make sure that the wiring related to the the code producing item isn't damaged.  Wiring problems will emulate failed components.  
Since the switch is wired thru the main harness, it's probably located on the valve body.  
This link will give you an idea of how to check the main harness for short or open circuit...you can move foward and backward and see a little more info.  Isn't as good as manual...but.  http://www.tpub.com/content/constructionpaletizedsystems/TM-9-2320-364-20-2/css/TM-9-2320-364-20-2_61.htm
I'd bet on a wiring problem...perhaps related to the pan injury.  

ATEC Code "66" indicates a comm link issue.  There are only 6 leads in the DDEC 1/ATEC link.  VSS, TPS, are included.  I'd guess that you have no transmision problems, but have a wiring problem.  

Pull the ECM fuse and clear the DDEC codes.  See what you get then.  You might be reading a whole series of codes.  That gets confusing.   ALWAYS verify that the ignition master is OFF before pulling any fuses from the DDEC or ATEC.  Keep in mind also that the DDEC and ATEC are always hot.  They have B+ input that is not switched by the master ig or battery disconnect.  Don't short anything out if you pull plugs.  
AND keep in mind that both DDEC and ATEC are 12V systems that operate from the center tap.  They will be fried if you connect the 12V input lead to the 24V post.   Then they'll flast all manner of codes....or non.   A good DDEC 1 will read a code "25" when no codes are set.   DDEC 1 units are famous for codes such as "low battery voltage," "injector...?"  These codes won't set a CEL, and won't have any effect on operation.  But the clutter up the code reading process.  
A DDEC code "55" indicates a trans comm link (TECL) fault.    

Try the DDEC again and see what happens.   Read the codes with the engine stopped, not when running.    

I've been planning on buying an ATEC manual...worry that something like this might pop up.  

JR
« Last Edit: May 25, 2011, 07:40:22 PM by NJT5047 » Logged

JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
luvrbus
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« Reply #23 on: May 25, 2011, 07:50:00 PM »

The 748 has 2 pressure switches forward and reverse fwiw

good luck
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NJT5047
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« Reply #24 on: May 25, 2011, 08:23:10 PM »


It looks like the reverse pressure switch is externally mounted?   From some pix on the 'net, looks like the FPS is mounted dead center of the valve body.   
The FPS can be evaluated by checking for continuity across the trans main harness plug.  I'd guess that it should be open when in neutral, or not running, or in reverse.  Closed when a forward gear is selected.  I'd guess. 
Pulling the main harness plug should allow an easy check once the layout of the plug is established while laying under the coach and looking at the plug upside down.  I believe the trans plug has tiny alpha stamped into the bakelite part of the plug?   That would be nice for someone young enough to focus on them!   Huh   
I wouldn't replace anything until diagnostics point to a mechanical failure such as a failed pressure switch.  Those things rarely fail.   Still, could be related to the damaged trans oil pan.  The FPS might have been damaged by the displaced filter or whatever holed the oil pan.   
I'm still not clear on when this problem presented...did the transmission shift funky prior to the oil pan damage?  Or did the problem begin with the oil pan hole?   
I'd highly recommend anyone owning an '86 or '87 MC9 with a DDEC 1 and ATEC buy a DDEC 1 Dx manual and proper ATEC transmission manuals and keep them in the coach.   Very few shops will work on a DDEC 1.   And a good many of those that will have no docs on the system.   It's quite different from a DDEC II and up.   DDEC 1 is a product of Motorola, DDEC II and up are Detroit designs.   DDEC 1 units are dependable, just that they have a ton of extra wiring and connectors and every inch can be problematic on an old coach.   
I'm not sure exactly what year th Pirate coach is, but if it's an '87 or later the coach suspension is considerably different from earlier MC9s.   '87 MC9 and MC12s share 102A3 style suspension.   And, if it's an NJT, everything else is different too. 

JR
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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
thepiratebus
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« Reply #25 on: May 26, 2011, 05:08:57 AM »

Thanks - will look into getting the book this week.  We'll try and clear all codes and try again.  the fps makes since since that is the main issue we are having.  Thanks for all the help
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« Reply #26 on: May 26, 2011, 06:28:53 AM »

the forward pressure switch is almost in the center of the valve body. the chances are great that it had been hit when you punctured the pan.

the switch is closed when under pressure ( gear selected)
so in order to measure it , it has to be removed from the body. apply 25-35 psi pressure and check if it closes (0 ohm resistance ).

or if your transmission has the (plastic like) connection plate inside the pan, you have a broken circuit in it.

the pressure switch connection 3 and 4 go to the transmission pan connector pin E and F

but with no pressure there should be no resistance on the switch.
so the only way to test it is to remove the pan and check the switch and internal wiring!


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thepiratebus
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« Reply #27 on: June 19, 2011, 07:15:30 AM »

Thanks for all the help - sorry for the slow reply, but I have been on the road.  We finally got around to working on the bus and it seems to be good to go.  We did a series of the recommendations and one or all together did the trick.  I wish I could pinpoint what fixed it, for other people who may have this issue, but while we had it jacked up we wanted to do it all. 

Before ordering the FPS, we decided to go easy and cheap.  Step one was to disconnect all battery sources so there was no possibility of power.  We assumed this would reset the AT comp.  At that time we also located a fuse that seemed to be blown.  This looked to be going to a aux source, but not sure what.  We had not noticed this fuse being blown before (it had a light on the fuse when blown and we think it blew when we hooked batteries back up).  New fuse installed.  We then drained all fluid and changed the AT filter.

After it all, it works perfectly.  Thanks for all the advice.  Happy trails!
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