Allison Troubles

[homermandy]

Allison HT-746 automatic in my Eagle 15. Cruising on highway for about 10 minutes, DO NOT SHIFT light goes on. Pull off on next exit, torque converter does not unlock. I stall the engine, check fluid, 4 qts too low. Start the engine up, take off, and the light comes back on and stays in whatever gear it was in last. However, it does not stall and torque converter unlocks. I am taking to service tomorrow. Just wanted to know if anyone had any clues. Engine is rebuilt < 1000 miles 6V92T. Thanks

[TomC]

First off-did you top off the trans fluid? Bus trannies have shallower pans for better ground clearance and 4 quarts low may be enough to start making the trans do weird stuff.  Try that first.  Good Luck, TomC

[Busted Knuckle]

First thing I'd do is change the fluid and filter if it was that low, it's been pretty hot and probably burnt! If that doesn't help it I'd check with an Allison qualified repair shop!  FWIW BK

[Sammy]

See if you can flash out the trouble code, might be a 51 - lockup solenoid.
Let us know what code you get, might be able to help a bit.
Sammy 

[homermandy]

Took it to local Detroit service center tonight. Dropped it off. Light didn't come on for a 30 minute ride. I suspect oil too low causing weird things to happen? They are going to run the coach with the Allison computer hooked up to it to check shift points, etc.  I just had a rebuild on the 6V92T and i notice excessive smoking when the trans downshifts. They are doing a few more tests on the fuel pressure, etc. I will keep you posted. Thanks

[homermandy]

Update:
They are still trying to locate the software for the HT746(scares me).  I am picking it up tonight regardless.  Strange thing is that when they test drove it, it would only go in re reverse and stayed in 1st gear. It would not shift. I am wondering if the Throttle Position Sensor might have something to do with it. OR a bad connection somewhere. It rode too good when I dropped it off for the 30 minute ride. Any suggestions? When I get it home tonight, limping in 1st maybe, where is the TPS located on the 746? Thanks

[homermandy]

Also, how do I flash out the codes without a reader? I have the keypad controller with 1-2-3-D and R-N.  Thanks

[Sammy]

You should have some type of diagnostic test switch, then code will flash out on the check trans light.
It might be near the trans ECU (computer).
See what you can do. If you can get a code, I'll help diagnose it for you.
I would also check the output speed sensor on the trans and it's connections.
Unplug the 2 pin connector and check the resistance of the sensor.
Let me know what you get.
Sammy 

[homermandy]

Thanks Sammy. I will check tomorrow. Turns out the Authorized Allison Detroit Dealer never found any software to read my Allison HT746. So it sat ther all week. Anyways, I picked it up(no charge) and started driving home. It stayed in 1st fear for about 5 minutes then all of a sudden the trans operated perfectly all the way home. I'm starting to suspect a connection or electrical problem. I need to get some manuals.

On a side note, I did get my 6V92T in-framed when I purchased the coach. I'm not sure why I get excessive black smoke on acceleration. I can understand on heavy acceleraction, but it seems it smokes a little too much. I get about 16PSI boost on a hill, new air filter, rebuilt blower. Any suggestions on the black smoke would be greatly appreciated. It is a DDEC2. Thanks

[Sammy]

I would check the turbo boost sensor. I believe there is a rubber line that connects to the sensor, it collapses or splits sometimes.
This will cause sensor to send wrong info to DDEC  ECM. If you have the "bypass"blower - (has a bypass valve on top, near rear) check the small rubber hose on it  - collapses or splits also.
Make sure all hoses and clamps on air intake and compressor sides of turbo are in good condition and secured properly.
Let us know what you find.
Sammy 

[homermandy]

Sammy,
Well, I am pretty happy tonight. I got under the bus to check resistance of 2 wire plug going into trans. Resistance was about 145 ohms. I then proceeded to check the large connector into the trans and it looked good. Didn;t want to unscrew it(wasnt sure if i should). Well I got to looking in the engine bay and looked at the tube from the turbo to thesensor and it looked fine. Then, low and behold, I looked at the turbo connection into the top of the blower I assume, There is a large rubber boot with 2 clamps(I assume to connect turbo to blower). THE ONE CLAMP(TOP ONE CLOSEST TO TURBO) WAS DANGLING. I could put my finger under the hose if I tried. When they did the rebuild, they must have forgot to tighten the clamp because it was actually DANGLING. Anyways, I tightened it down and will test tomorrow. Makes sense though that that massive air leak would cause less air into the blower. I'm keeping my fingers crossed that this is the black smoke issue. I will try tomorrow and let you know. Also, does the resistance sound right for the plug into the trans? Thanks

[Sammy]

Resistance value is good - range is from 115 to 165 ohms.
Glad you found a loose hose.Hopefully that's your black smoke problem.
Now about the ATEC codes... did you try to "blink' or "flash" them out?
Your local dealer needs an ATEC cartridge and a Pro-Link.
Try a local transit garage,they might have one. Many transit coaches have ATEC.
If you lived closer I'd come do it myself for you,LOL.
Sammy 

[niles500]

http://www.tpub.com/content/semis/TM-9-2320-364-20-1/css/TM-9-2320-364-20-1_170.htm

http://www.tpub.com/content/semis/TM-9-2320-364-20-1/css/TM-9-2320-364-20-1_171.htm

http://www.tpub.com/content/semis/TM-9-2320-364-20-1/css/TM-9-2320-364-20-1_172.htm

http://www.tpub.com/content/semis/TM-9-2320-364-20-1/css/TM-9-2320-364-20-1_173.htm

http://www.tpub.com/content/semis/TM-9-2320-364-20-1/css/TM-9-2320-364-20-1_174.htm

http://www.tpub.com/content/semis/TM-9-2320-364-20-1/css/TM-9-2320-364-20-1_175.htm

http://www.tpub.com/content/semis/TM-9-2320-364-20-1/css/TM-9-2320-364-20-1_176.htm

for general info on ATEC's - HTH

[homermandy]

Wow, Thanks Niles. I will try that today. I appreciate all the help.

[homermandy]

Ok, here is the latest. I took the bus for a test ride after tightening up the clamp on the turbo. OMG. Talk abotu night and day. No black smoke, turbo kicks right in, got up to 80 on highway and had to back down. Boost read as high as 21lbs. Wow, now this is what a newly rebuild motor should do.

Now the bad part. Coming back on the highway, DO NOT SHIFT light goes off. I have to get off at an exit and it stays locked in 4th. I turn off the engine since it is bucking from not unlocking torque converter. Turn back on, switch to drive and get back home with no more light.

Good news is I actually have a diagnostic switch on my dash for engine and trans. I actually got the eninge to flash codes of:
36
43
44
45
58
36
43

Not sure what they mean, Anyone?  Now the trans diagnostic light does light up before I start the engine, but when I hit it's diagnostic button, no codes flashed. I'm assuming there may be no codes?

My other theory is both times the DO NOT SHIFT light beeped was on the highway, hot day, and really getting on it with the motor.  Now I  do have a Trans Temp guage, but it does not work. I have not traced the wire from the guage, etc. Guage may actually be broken, Where does the guage get it's signal? The computer? Also. do you think switching to synthetic will cure the problem if it is overheating?  I currently have Allison approved Coastal brand ATF in it now. 

Odd thing is. when I changed the trans fluid last month to Coastal, I did drive the bus about 400 miles to Kentucky back to Ohio in some super hilly areas and the DO NOT SHIFT LIGHT did NOT come on. Which makes me think my theory of overheating may not be right?

Geesh, at least I'm happy about the motor. Now I need to get this annoying trans thing fixed. Also, any idea on the motor codes?

Thanks for all the help.