Allison Transmission upshift problem

[DanK]

I am having a shifting issue with the Allison Transmission and I thought I would post it here to see if anyone had any insight on what it could be. The coach is a 2003 Newmar Kountry Star with the ISB 300HP motor and the Transmission is the 3000 series. The issue is that when I'm towing a vehicle behind the coach and I'm climbing a steep grade the coach downs shifts properly, but will not upshift properly. Example would be driving half way up a hill and the RPM will go to about 2400 after down shifting and would normally start to upshift at at around that RPM, but it goes in between gears. So the transmission tries to upshift, but doesn't actually upshift (I hope that makes sense). I have taken to coach into our Allison dealer and they could not simulate the issue, so they did not know what the issue is. The issue only happens when towing and only on very long grades. The other thing to mention is that when it tries to upshift is tries to do it every 1-2 seconds until I back off the on the gas pedal and then it will upshift. The problem is also starting to occur more frequently. I have owned the coach since new and it only started about 1000 miles ago. Coach have 67K milage if that is a factor. I would appreciate any insight you may have.

[Mike_Hohnstein]

Manually selecting ranges is the correct strategy, engine 'governor' has nothing to do with the transmission shift program, that input is from the forward drum sensor, front curb side of the unit.

[DanK]

Ivylog wrote:
Not sure how much more money I'd throw at this possible problem until it gets worse... if it does.

The problem is it is getting worse and happening more often. The plan is to take it to Cummins to see if they can simulate and hopefully find a solution.

Thank you all for your informative responses.

[Ivylog]

While I agree things out of the ordinary are troubling I almost always manually select a gear on a long up/down hill. Seems like I end up behind a car that brakes for every turn requiring me to get out of the gas enough that the Allison will up shift otherwise. Not sure how much more money I'd throw at this possible problem until it gets worse... if it does.

[wolfe10]

usersmanual wrote:

DanK wrote:

wolfe10 wrote:
Assume you have checked the Allison for diagnostic codes with the shift pad. Any codes?

Yes I have, and when it was at the Allison service center they had a computer hooked up while driving the coach and that didn't turn up anything.

try and drive it as I do mine. On a long loaded uphill pull I manually select the gear that works best and leave it there till I get near over rev and then manually select the next gear
or I back off a bit and just maintain constant same RPM

I do exactly the same-- it totally prevents "hunting between gears" which is hard on any transmission.

[DanK]

rgatijnet1 wrote:
Have you taken it to the Cummins shop to see if the engine control module is sending the proper signals to the transmission?

I spoke to Cummins today and will try to get it in there shop this week or next. They said they had a Dyno and could try to simulate it that way, but if it didn't have the shift issue on the Dyno, it would be hard for them to find the cause.

[DanK]

usersmanual wrote:

DanK wrote:

wolfe10 wrote:
Assume you have checked the Allison for diagnostic codes with the shift pad. Any codes?

Yes I have, and when it was at the Allison service center they had a computer hooked up while driving the coach and that didn't turn up anything.

try and drive it as I do mine. On a long loaded uphill pull I manually select the gear that works best and leave it there till I get near over rev and then manually select the next gear
or I back off a bit and just maintain constant same RPM

Yes, that is what I end up doing to get around it, but that is just a work around. I want to make sure it operates correctly and find the root cause.

[rgatijnet1]

Have you taken it to the Cummins shop to see if the engine control module is sending the proper signals to the transmission?

[usersmanual]

DanK wrote:

wolfe10 wrote:
Assume you have checked the Allison for diagnostic codes with the shift pad. Any codes?

Yes I have, and when it was at the Allison service center they had a computer hooked up while driving the coach and that didn't turn up anything.

try and drive it as I do mine. On a long loaded uphill pull I manually select the gear that works best and leave it there till I get near over rev and then manually select the next gear
or I back off a bit and just maintain constant same RPM

[DanK]

wolfe10 wrote:
Assume you have checked the Allison for diagnostic codes with the shift pad. Any codes?

Yes I have, and when it was at the Allison service center they had a computer hooked up while driving the coach and that didn't turn up anything.

[wolfe10]

Assume you have checked the Allison for diagnostic codes with the shift pad. Any codes?

[usersmanual]

DanK wrote:
It's doesn't feel like an injector misfire because it feels like the trans is going through the motions of trying to shift, but wont. Your theory of the engine governor telling the trans to shift, but the trans is saying no because it still feels the load is logical to me, and would fit what I'm feeling.

Ok it was just a idea that crossed my mind.

[DanK]

It's doesn't feel like an injector misfire because it feels like the trans is going through the motions of trying to shift, but wont. Your theory of the engine governor telling the trans to shift, but the trans is saying no because it still feels the load is logical to me, and would fit what I'm feeling.

[usersmanual]

DanK wrote:
Thanks all for your input. I'll try to answer all your questions in hopes to find out what is going on.

1. Yes I have followed the recommender service intervals and have changed out the fluid to Transynd as well as both filters. I also checked the fluid and it is correct.

2. I would agree that the transmission should stay in the lower gear until I reach the top of the grade, but what happens is it tries to upshift but doesn't actually upshift. So it goes into that range between normal shifts, but doesn't actually shift up or down. When it get's in that range it tries to shift every 1-2 seconds, so it jerky (my technical term) while it's in the mode.

3. Pedel is completely compressed when it happens, but also will do it if not completely depressed.

4. Correct that the Allison service center was not able to diagnose, but they were also trying to simulate it and because they could not get the conditions right, were not able to track down the issue. The one thing they said was that they thought it was because the engine was not powerful enough, but the power has not changed since I purchased the MH and again this is a new problem that came up about 1000 miles ago.

Ok that's helps me to understand whats up. Just a off the wall thought here? maybe its a injector misfire? maybe its not the trans
at all? it will be a real jerky feeling like you describe

[DanK]

Thanks all for your input. I'll try to answer all your questions in hopes to find out what is going on.

1. Yes I have followed the recommender service intervals and have changed out the fluid to Transynd as well as both filters. I also checked the fluid and it is correct.

2. I would agree that the transmission should stay in the lower gear until I reach the top of the grade, but what happens is it tries to upshift but doesn't actually upshift. So it goes into that range between normal shifts, but doesn't actually shift up or down. When it get's in that range it tries to shift every 1-2 seconds, so it jerky (my technical term) while it's in the mode.

3. Pedel is completely compressed when it happens, but also will do it if not completely depressed.

4. Correct that the Allison service center was not able to diagnose, but they were also trying to simulate it and because they could not get the conditions right, were not able to track down the issue. The one thing they said was that they thought it was because the engine was not powerful enough, but the power has not changed since I purchased the MH and again this is a new problem that came up about 1000 miles ago.