Do Not Shift Light Flashing Allison 748 ATEC

[Scott & Heather]

Can you tell me what an HT740D is? Specifically what does the "D" denote?


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[blue_goose]

From what you have said, sure sounds like the speed sensor.  That is the one on the front of the transmission.
Jack

[chessie4905]

Since you run year round in salt and slush at times, carefully inspect connections at transmission. If it turns out to be a corroded connection, after repair, securely clean and seal connection area to avoid a repeat in the future.

[luvrbus]

Thanks Solar...I'm flying out of town for a couple weeks so I'll have to chase this down later unfortunately. Geoff, I am absolutely convinced after a mere three years of ownership that I would rather have my mechanical 6v92 and Allison HT740 back any day...seriously.


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think about it for a second the electronics on your bus are almost 30 years old,mechanical engines and the 740 would give problems too,lol I starting to get the hang of the electronics and sorta of like it   

[John316]

Hey Scott,

I am in the KC area. If you need help, or you need a place for your wife and kiddos to stay if the bus is not parked in a good spot, let me know. My wife and I are a young couple and happy to help in anyway possible.

Best,

John

[chessie4905]

The majority of the issues on these older electronic engines are poor or intermittent connections. Most of the time, in the engine area, as the water, salt, road debris, gets sprayed around everywhere on the road, and over time degrades connections. Newer models have combatted most of the issues by using better connecting designs with double and triple seals on connectors, improved securement of wiring and harnesses. Be careful how you probe for resistance in wiring issues. Gone are the old days of pricking wire insulation. Quick way to introduce new corrosion point. You need to know how to use a vom meter and understand electricity and electronics to some degree. Using a scan tool is extremely useful, however you still need the meters once the scan tool points to the issue. Just throwing parts can get costly. Sometimes you are lucky. Most of the times you arent.

[Lee Bradley]

Best of luck! Mine did that but I went through reset and it went to neutral and the light stayed on and would not shift.  New manufactured transmission; all better. 

[luvrbus]

When you are dealing with a 1st generation electronic Allison all things are possible from minor to major problems and now most Allison shops don't offer much support 

[thomasinnv]

I chased a similar problem last summer for a while. Went through a couple of speed sensors before I found a loose pin on the plug at the sensor. Only way i was able to find it was by unplugging the harness at the trans ecu and connecting a vom and had my wife watch the meter while i started wiggling and pulling on every inch of the harness. When i got to the plug on the speed sensor the meter started going all over the place. Alison shop wanted over $600 to run a new twisted pair from the ecu to the trans sensor and new plug. 10 seconds to spread the pin with a little pick and we were off, and kept the $600.

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[Scott & Heather]

Crazy stories!!  ATEC trans are crazy beasts. If it were my TPS my ddec would throw a code which it's not. So I'm leaning towards what most of you are suggesting that connections somewhere are loose or corroded cause Chessies right, we've recently been in heavy snow and salt spray. When I get back from D.C. I'll be tearing into this.


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[eagle19952]

When I get back from D.C. I'll be tearing into this.


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Congressional hearing ?

[Scott & Heather]

Lol. No. I'm staying as far away from any politically active locations as I can. I'm there singing for some meetings for a week.


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[buswarrior]

The rule, with few exceptions:

The harnesses were ALL compromised by mechanics.
30 years ago, they pricked wires with probes to solve electrical problems.

It took beatings, and retirements, to make it stop.

Some of these a$$es, and their protegés are STILL out there today, jamming sharpened probes down the back of connectors, or straight into the wires.

Those in the salt find out sooner, the rest find out later...

Re-wiring is going to figure just a prominently as insulating in the lives of busnuts, as the electronic equipped buses end up in every backyard.

Happy coaching!
Buswarrior



Happy coaching!
Buswarrior