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Author Topic: NEED HELP AGAIN OR STILL  (Read 1106 times)
TVDAD
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« on: June 19, 2007, 02:51:32 PM »

I am the person with The don't shift light problem. It has been determined that the ATEC or ECU is bad. Does anyone have or know someone who has an ATEC for the HT 748 the part number appears to be 29502534 Nimco doen't appear to have that part number.
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niles500
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« Reply #1 on: June 19, 2007, 10:38:48 PM »

Tom - don't think I'm crazy - BUT - before everyone tells you I AM - disconnect your ATEC, DDEC from its power source for a 10 minute perod and "cold start" it to see if you still have a "no shift" indicator - I'm bound to get flamed for this but - HTH
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Sean
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« Reply #2 on: June 20, 2007, 12:25:20 PM »

You'll need the services of a professional shop that works on Allisons...  this is not just a swap-the-part type of fix.

Assuming you do find an ECM (and, by the way, I would give Virgil Cooley a call over at PEDCO in California -- last time I was there, he had plenty of 74x trannys and probably some ECMs), you will still need to have YOUR program loaded into it.  Each and every 748 ECM is specifically programmed for the correct application (meaning what engine it is mated to, rear end ratio, where the correct shift points are, etc.).  IIRC, the first-generation ATECs (AKA "CEC1") are EPROM-based (unlike, for example, the DDEC-II which can be reprogrammed in the field).  And the program has to come direct from Allison HQ.

If I were in your shoes, I would bite the bullet and get the authorized Allison dealer involved.  Since you can't move the coach, they will come to you for an extra charge, or you can pull the ECM (simple, really -- three or four connectors and four bolts) and bring it in to the shop.  They can bench-test it, get you a reman if needed, and they have access to your programming information (which is kept by Allison forever) to re-load it, even if your original ROMs are fried.

HTH.

-Sean
http://OurOdyssey.BlogSpot.com
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Full-timing in a 1985 Neoplan Spaceliner since 2004.
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TVDAD
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« Reply #3 on: June 20, 2007, 02:43:16 PM »

It is at Allison shop and they want $4,000.00 to replace it
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Sammy
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« Reply #4 on: June 20, 2007, 04:36:35 PM »

Sounds like too much $$$$$$$$ to me.
I took an ATEC ECU from a bus with an HT748 trans and installed it in a bus with a V731 trans. Both vehicles were ATEC controlled transmissions. I swapped the PROM from the original V731 bus into the ECU from the 748 - donor bus. Worked fine.Both ECU's were the "Sealed Standard/Sealed Plus II type.
The PROM is located under the small cover with 4 small bolts, on the back of the ECU.
The PROM has all trans shift and control info on it.
It has a label to tell if it has been tampered with, I didn't care. Might be worth a try.
If you want to try it, call NIMCO again and ask for an ATEC ECU from a  bus that has the same style of ECU that you have.Tons of transit buses had them. Try a local transit garage too.
WTEC does NOT have a servicable PROM, gotta go to the Allison dealer to have the program burned to it.
New WTEC ECU's do not come programmed - WTEC2 or WTEC3.
Hope this might help you. Best of luck with your repair.
Sammy  Cool
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NJT5047
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« Reply #5 on: June 20, 2007, 07:07:47 PM »

It is at Allison shop and they want $4,000.00 to replace it

Replace what?  Just the ATEC ECM?? 
What is their diagnosis?
I've seen used ATEC ECMs for $300-$400 bucks for 6V92TA/HT748R with 3:70 drive axles.   And I've seen them for more.  For $4k you could buy a complete donor transit and drive it home.
Do they indicate your transmission has failed?
Sounds like you need a second opinion.   
 
JR

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

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« Reply #6 on: June 20, 2007, 08:47:28 PM »

Sorry you hid your e mail from us or I'd try to help a little more.
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