Transmission won't shift, etc.

[Keith Oliver]

First trip out this year. not without its issues:

First symptom that all is not right, the engine brake active despite the accelerator being used.
Next, after shutting down at the ferry lot, a drive of 10 km, ready to leave Saltspring Island, startup worked fine, but then trans wouldn't shift into gear, for about a minute, then ok, into gear.  Next, aboard the ferry, trans wouldn't shift to neutral.  I tried for only a few seconds, then turned the key off.  Engine shut down, but beeping continued for at least a minute before stopping.
Time to go off the ferry, wouldn't start, with a red light on the trans key pad, but no other symptom to help.  Every other car off the ferry and all the deckhands gathered around.
Eventually, I held the battery combiner down for several second and the red light on the trans pad extinguished.  Then when I tried the key, the engine started.  Got off the ferry!  
My wife following in the car, noted that the brake lights were on the whole way home to Coquitlam, a 60 minute drive.  In the first 5 miles, everything working properly for a while, then the trans refused to upshift for about a mile following a stop light, then shifting properly the rest of the way home.  By this time I had turned the exhaust brake off, and it didn't seem to want to come on by itself.  In the last ten minutes of the drive, the lighted display on the trans pad went black and stayed that way  till I got to the house and it shifted properly to neutral. Before shutting down, I tried to shift to Drive once more, but it would not.
Any ideas?

[Keith Moffett]

I notice that you don't mention any transmission codes.  Have you run the test?
I assume the tranny fluid is up on the dip stick?  This is just a coarse check, fluid level is checked on the test sequence.
Have you serviced the exhaust brake?  A stuck selenoid might send confusing signals to the tranny.
Have you had any overheat problems on the tranny recently?

This is just food for thought.  Many others here are better informed than am I.

Best
Keith

[Keith Duner]

This comment will be of limited help since I don't the wiring for your coach (or mine for that matter...) however the symptoms you describe would reasonably lead someone to check the power and ground to the transmission TCM. "Illogical behavior" from any electronic control system is frequently the result of temporary loss of either power or ground or marginal values for either, (that conclusion might be supported by the comment about "holding down the battery combiner").   As noted by Keith above, check for codes by using the up and down arrows on the shifter key pad (process details available in the Allison Operators Manual for your transmission).  If batteries and power and ground supply to the transmission TCM can be confirmed as good you should consider contacting an authorized Allison service outlet at your earliest opportunity.  Good luck.  (I'm a retired Allison Transmission factory Customer Support manager).

[Edward Buker]

You mentioned that you had to use the battery combiner to get the engine to start at one point. If voltages were low and marginal due to a bad battery it could cause the computer logic to be incorrect and the sensor values to not be in spec.  There were so many things going on here that it would seem that either your transmission computer is faulty, the plug to it has corrosion/contact issues, or the exhaust brake being on constantly has put sensors out of limits for the transmission to work properly.

The fact your brake lights were on constantly the whole trip would indicate that the transmission was probably getting the signal of exhaust brake being on and that being the first symptom when you started up would seem like a good place to start. If you got that problem sorted out and corrected you could see what happens next.

Also verify that you are getting 13.8V or so on the house and chassis batteries after start up to rule out battery low voltage issues playing a role here. Hope this gremlin is an easy one to track down and whack with a hammer....

Later Ed

[Keith Oliver]

Thanks for your ideas.
First order of business today was to find someone who could get diagnostics off of the Trans.  That turned out to be the local Allison service  center.  Drove out there this afternoon and left the coach with them.  Brake lights still on.  Trans working ok.  The tech put a plug in under the dash and found that there had been 7 events of "not shifting", but the last two starts had none.  Tomorrow I will learn whether anything serious is wrong.

Keith and Keith;  I am too ignorant of the Allison, as it has previously been perfect, and didn't realize I might get the codes myself.  I'll need to see if I have the manual you refer to when I get the coach back.  Never had a warm tranny, let alone overhot.  fluids all ok. haven't looked at the exhaust brake yet as the problem seemed electrical.

Ed:  voltage when running was good, according to the dash voltmeter.  Using the combiner wasn't necessary to start once the trans would permit a start, hadn't been used to start the previous few times.  I was just using it as part of fiddling around when it was refusing to allow cranking of the engine.  

30 minute drive to the Allison shop.  Again the brake lights on most of the way.  Trans working ok, exhaust brake working when the switch on, not when off, so seems ok, except for the lights staying on.  

[Keith Oliver]

Transmission codes indicated a failed control panel, which has now been replaced and worked perfectly all the way home.  The brake lights being on all the time may have been going on for a while, as it is solved by lifting up on the pedal.  I'll fix that tomorrow.  

[Bill Sprague]

Good news!

[Edward Buker]

Kieth,

Good to see that it was something simple...that is one fail that I would not have expected.

Later Ed

[Keith Duner]

Good news! Another problem "in the rear view mirror".

[Keith Oliver]

One other thing I learned from the guys at Cullen Detroit Diesel, the associated co to Allison, and part of this diagnostic trip, is that the way the exhaust brake is supposed to work, is that when the switch is on, merely lifting my foot from the accelerator will activate the Pac-Brake.  This is what is now happening, but not the way it worked before the beginning of this trip.  I am still not convinced.  I just don't see how it could have been working differently before the Allison control panel failure, and suddenly changed to now work "correctly".  Just to be perfectly clear, it used to allow the switch to remain in the "on" position and not activate until I touched the brake pedal, de-activating as soon as I touched the accelerator.
Gerald, I hope you can tell me which way is really the way it is supposed to work.

[Gerald Farris]

Keith,
All of the SMC era Beavers (1995 to 2002) that I have had experience with engaged the exhaust/Jake brake as soon as the accelerator is released if the switch is on just like your coach is operating now. With the coach wired this way the cruse control will not operate when the exhaust/Jake brake switch turned on, however the wiring can be changed on most coaches to enable the cruise control to operate when the exhaust/Jake brake switch turned on and the exhaust/Jake brake will only activate when the brake pedal is depressed.  

Gerald

[Keith Oliver]

Thanks Gerald.  Do you know of any way my coach would revert back to the "usual" way, when since I have owned it, until the transmission started acting up (coincidence?) it has always allowed the cruise control to operate and the exhaust brake was activated only by touching the brakes?
Then, what needs to be changed to get it back to the way it was?

[Gerald Farris]

Keith,
I am sorry that I do not know of any correlation between the two problems. I have only seen one coach (a 2000 Marquis) were the wiring was changed to allow cruise control operation with the engine brake switch in the on position, and I am not sure what changes would be necessary to achieve the same results on your coach. It would just require a lot of looking and circuit chasing for me to determine the necessary changes.

Gerald

[Keith Oliver]

Gerald:  What I don't get is how this could switch from having the EB operate with the switch always on and activation is by touching the brake pedal to activation by lifting my foot from the accelerator.  I didn't change any of the wiring.  
I don't know if I might like the present way it works, after driving a few thousand miles, I just would like to understand how it switched itself to the other setup.

[Gerald Farris]

Keith,
I am sorry that I can not answer that for you.

Gerald