Community Forums

pointrow · 06-18-2019, 11:29 AM

Cruising along at 70 mph on flat road and transmission down shifted for about 2 seconds and returned to 6.6. I think it did it once before but this is the first time I caught it.
Any ideas what happened and is it anything to have checked out?
Allison 3000, 450 hp. 47000 mi.
Thanks.

Skip426 · 06-18-2019, 05:52 PM

OK , a little info on Allison shift priorities .

In order to determine the engine's load and downshift , the trans controller , looks at it's program for engine RPM vs Throttle positioning sensor reading .
So anything that restricts engine RPM for the TPS reading can cause the trans to downshift OR restrict up shift to higher that usual speed .

Fuel filters , air filters , anything that can have the slightest effect on engine power can mess up the shifting.

Were you running on Cruise Control at the time?

pointrow · 06-18-2019, 07:04 PM

Quote:

Originally Posted by Skip426

OK , a little info on Allison shift priorities .

In order to determine the engine's load and downshift , the trans controller , looks at it's program for engine RPM vs Throttle positioning sensor reading .
So anything that restricts engine RPM for the TPS reading can cause the trans to downshift OR restrict up shift to higher that usual speed .

Fuel filters , air filters , anything that can have the slightest effect on engine power can mess up the shifting.

Were you running on Cruise Control at the time?

I don’t think I was on cc. Thanks for the ideas.
Fuel, air filters are both fresh.
I wouldn’t have noticed it but I noticed the rpms were high then figured out what just happened.
I’ll keep an eye on it and see if it happens again.
Thanks

dbarton291 · 06-19-2019, 01:42 PM

Quote:

Originally Posted by pointrow

I don’t think I was on cc. Thanks for the ideas.
Fuel, air filters are both fresh.
I wouldn’t have noticed it but I noticed the rpms were high then figured out what just happened.
I’ll keep an eye on it and see if it happens again.
Thanks

What RPM do you cruise on at 70?
What was the "high" RPM you noticed.

pointrow · 08-29-2019, 06:26 AM

Update kind of. On road yesterday and it did it 5 times in 3 hrs. Happened to check trans temp and it’s jumping all over the place and never seems to be high enough to be accurate.
Me thinks I have a loose connection some place.

Skip426 · 08-31-2019, 12:47 PM

First place to check, would be the main trans to chassis connection within 15 " of the trans . The round connector has lock nut to keep it tight and water proof .
If your shifting / trans temp issue is related to road moisture ( worse in the rain) that's the place I'd look .