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Old 05-17-2020, 05:09 AM   #1
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Ongoing hard shift issue

Hello! Looking for some advice in troubleshooting a consistent hard shifting issue. It's a 1999 American Dream, with a Cummins ISC and an Allison MD3060. Here's the symptom:

When starting from a complete stop, engine needs to rev past ~1800 RPMs to shift into 2nd. This is always consistent, no matter the throttle input. Then, the shift into 3rd is always BANG! Super hard. Once in 3rd, it's smooth sailing through the rest of the gears. It has been like this since I've owned it - purchased in November 2019. Previous owner said a shop told him that's normal - will smooth out when towing. It can't be normal, though - and it didn't improve when towing. I've tried varying throttle inputs, but the hard shift just can't be avoided.

Here's what I've done for troubleshooting. I initially checked transmission codes, and there was a 22-14 - Speed sensor error. So I checked the sensors - ohmed them out, and both were in spec. Swapped the front and rear, cleared the code, and it did not return. Didn't improve the issue, though.

I've changed the fluid and filters to Transynd - no improvement.

Changed the diff oil.

Did a 200 mile trip, towing 6,000 pounds, and a code 66-00 appeared - serial communication interface fault. I checked the connections at the ECU - all clean and tight. I have been unable to reach and take apart the connections on the engine computer yet.

Also took apart and cleaned the ground lug and connectors.

Checked the throttle position sensor behind the throttle pedal - checked out fine.

I contacted the guy at Transmission Instruments, thinking my ECU could be flaking out, but he told me they don't diagnose hard shifting issues.

I've done a lot of searching on this issue, but haven't come across a similar post. I suppose the next step is to get it into an Allison repair shop, but all of the ones nearby have terrible reviews - if you're in the South Florida area and can recommend a shop, I'd appreciate it! Or, if you can suggest another troubleshooting step, I'm all ears! Getting ready to do a 6,000 mile trip in a few weeks, so would love to get this issue fixed! Thanks so much.
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Old 05-17-2020, 05:29 AM   #2
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Forgot to mention that I have no engine fault codes.
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Old 05-17-2020, 05:34 AM   #3
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Try calling Allison's help line. They were great when we had a transmission failure while on the road. They not only correctly diagnosed the problem, but they recommended a shop that was qualified to handle the repair. The technician I spoke with also warned me not to take it to "just any Allison shop that just performs fluid changes", but to a particular dealer shop that had the expertise to handle the problem in my transmission.
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Old 05-17-2020, 09:55 AM   #4
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FWIW FDDA is the Allison distributor in Florida. I'd take it to one of their shops.

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Old 05-20-2020, 05:25 AM   #5
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Thanks for the replies. I did call Allison, and was told that the help line is more for oil changes than to diagnose shifting issues - he referred me to a service center, which is about an hour away! It is a FDDA.

Soooo, any other ideas out there?
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Old 05-20-2020, 05:35 AM   #6
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Quote:
Originally Posted by castlemusic View Post
Thanks for the replies. I did call Allison, and was told that the help line is more for oil changes than to diagnose shifting issues - he referred me to a service center, which is about an hour away! It is a FDDA.

Soooo, any other ideas out there?
Well that is a surprise. When I called the tech spend a considerable amount of time getting me to press several 'secret' key combinations to get into a place where more codes are stored. Then he had me clear them and drive the motorhome again a short distance to see if they reappeared. They did. That was when he knew where the problem was and recommended a shop that was 52 miles away on the opposite side of St Louis from where we broke down. We had to be towed to that dealer.
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Old 05-20-2020, 06:45 AM   #7
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I'd take another look at the TPS and your Throttle linkage. Make sure there is no slack in the cable and linkage. I know Mine is much older than your but my TPS is located in the Engine compartment and is activated from the Linkage.
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Old 05-20-2020, 10:34 AM   #8
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I'd take another look at the TPS and your Throttle linkage. Make sure there is no slack in the cable and linkage. I know Mine is much older than your but my TPS is located in the Engine compartment and is activated from the Linkage.
On mine, there's an electronic sensor on the throttle pedal (Williams Controls) which sends the throttle signal back to the engine. I'm calling that the TPS, but maybe that's not the right name for it. I have not checked the throttle linkage on the engine - will snoop around for that.
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Old 05-21-2020, 12:06 PM   #9
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Anybody know where would I find this box on my coach? (99 American Dream) It's called a Vehicle Interface Module (VIM), and I haven't come across it yet to check connections there.
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Old 05-21-2020, 05:32 PM   #10
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You to to an Allison service center and get that Diagnosed !
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Old 05-23-2020, 07:14 AM   #11
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The DD-Allison Service Center in Fort Pierce is an excellent shop.


That is where I would take it.
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Old 05-28-2020, 07:14 PM   #12
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Just to follow up, the Allison tech reset my tcm, clearing all saved shifting data, so it would relearn all shift points. I had my doubts that this would help my problem, but sure enough, after paying my $187 and heading out, I'll be darned if the hard 2-3 shift was gone! It's nice and smooth right up through all gears! Downshifts seem to be a little harsher than before, but will probably smooth out as it relearns.

I'm a happy camper! Thanks for the advice.
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Old 05-29-2020, 05:01 AM   #13
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Quote:
Originally Posted by castlemusic View Post
Just to follow up, the Allison tech reset my tcm, clearing all saved shifting data, so it would relearn all shift points. I had my doubts that this would help my problem, but sure enough, after paying my $187 and heading out, I'll be darned if the hard 2-3 shift was gone! It's nice and smooth right up through all gears! Downshifts seem to be a little harsher than before, but will probably smooth out as it relearns.

I'm a happy camper! Thanks for the advice.
Interesting! Thanks for getting back to us, and please keep us posted.
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Old 05-30-2020, 12:31 PM   #14
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Anybody know where would I find this box on my coach? (99 American Dream) It's called a Vehicle Interface Module (VIM), and I haven't come across it yet to check connections there.
My VIM is mounted to the right of the genny (as you face the genny from outside) on the firewall.
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