Wierd 68 rfe shifting

[TJJEEPER]

Just returned from a 2600 mile trip through the west. During the trip, in the morning everything worked just fine. Down shifting properly on grades like it should. After the outside temps warmed up or a couple hundred miles it wouldn't properly downshift on grades.

Details: 10' slide-in camper, pulling trailer @ about 3,000 lbs, signature truck with 3.73 gears and under 28,000 miles. Running between 65 and 70 on the cruise control. When working properly it would downshift after losing around 4 to 5 MPH. When not it would lose over 5 mph and continue down before I'd manually downshift, usually from 6th to 5th. Sometime this shifting was due to a grade and sometime due to a strong headwind.

Just curious... Trans was services less than 5,000 miles ago because the truck is 95% used for towing a 5th wheel or loaded with camper.

Thoughts?

 

[Cummins12V98]

TH and EB on all the time?

 

[TJJEEPER]

TH and EB on all the time?

Yes

 

[Cummins2014]

TH and EB on all the time?

I know you seem to stress this, but yes the tow haul does hold the gears longer, but his shifting is something besides having the tow haul on. I don't see any change in shifting other then holding the gears longer in tow haul.

 

[Cummins2014]

Just returned from a 2600 mile trip through the west. During the trip, in the morning everything worked just fine. Down shifting properly on grades like it should. After the outside temps warmed up or a couple hundred miles it wouldn't properly downshift on grades.

Details: 10' slide-in camper, pulling trailer @ about 3,000 lbs, signature truck with 3.73 gears and under 28,000 miles. Running between 65 and 70 on the cruise control. When working properly it would downshift after losing around 4 to 5 MPH. When not it would lose over 5 mph and continue down before I'd manually downshift, usually from 6th to 5th. Sometime this shifting was due to a grade and sometime due to a strong headwind.

Just curious... Trans was services less than 5,000 miles ago because the truck is 95% used for towing a 5th wheel or loaded with camper.

Thoughts?

You are saying in cruise control, after it gets warmer it won't downshift out of sixth when pulling a grade or in a head wind? You have to do it manually ?. How about when not in cruise, and you are on the throttle does it downshift, or are you having to manually downshift ?

Although I normally run locked in fifth when towing my fifth wheel, It usually doesn't take a lot of grade or whatever to downshift to fifth, so I just leave it in fifth most of the time, so its not hunting gears. Good flat road I will leave it in sixth, but thats not often.

 

[TJJEEPER]

The point is it exhibits two different characteristics when hot or cold. Works like I'd expect when cold and doesn't when hot.
It'll pull just fine in 6th and I get better mileage. When it doesn't downshift it will continue bog to the point where when it does downshift it'll go to 4th OR will drop the cruise.

BTW The trans temp is "normal" when this happens... between 180 and 190

 

[Cummins2014]

That sure isn't normal, you do have some problem. Mine will lose 5 mph or so, and then downshift to fifth , if I am not locked in fifth when towing. Never in fourth unless there is a pretty steep grade, but at that point I am on the throttle. I get out of cruise on the steep grades. I want to control the speed, throttle, etc.

 

[transe]

I don't think the problem is the trans itself, but rather the controls. If the PCM was commanding the trans to downshift (and it didn't), it would blow a fault code. Since you apparently have no faults, I imagine the PCM is never commanding the downshift (or TCC unlock). Why that would be, I have no clue, but don't go chasing the wrong thing. The problem is likely in the controls somewhere.

I would get some kind of scan tool where you can monitor the current gear, target gear, and TCC state. That will show you what the PCM is commanding. You might also check the throttle opening (and output speed) under the downshift conditions, cold vs hot. Downshift points are based on output speed and throttle, so maybe when truck is fully warm you're running at lower throttle level than when cold (so it has to open the throttle further from the cruise state to hit the downshift point).

 

[Cummins12V98]

I know you seem to stress this, but yes the tow haul does hold the gears longer, but his shifting is something besides having the tow haul on. I don't see any change in shifting other then holding the gears longer in tow haul.

Really don't care to hear from you as all you do is criticize. Stick to commenting to the OP.

 

[Cummins2014]

Really don't care to hear from you as all you do is criticize. Stick to commenting to the OP.

I fail to see the criticism on my reply to you on THIS thread, seems you are getting a little thin skinned. I don't see where the tow haul or EB would have anything to do with his problem, but who knows until he gets it looked at.

 

[TJJEEPER]

I don't think the problem is the trans itself, but rather the controls. If the PCM was commanding the trans to downshift (and it didn't), it would blow a fault code. Since you apparently have no faults, I imagine the PCM is never commanding the downshift (or TCC unlock). Why that would be, I have no clue, but don't go chasing the wrong thing. The problem is likely in the controls somewhere.

I would get some kind of scan tool where you can monitor the current gear, target gear, and TCC state. That will show you what the PCM is commanding. You might also check the throttle opening (and output speed) under the downshift conditions, cold vs hot. Downshift points are based on output speed and throttle, so maybe when truck is fully warm you're running at lower throttle level than when cold (so it has to open the throttle further from the cruise state to hit the downshift point).

Thanks, that was kinda my thoughts too. Transmission/throttle would respond fine when shifted manually and left in cruise mode.

 

[Cummins12V98]

I fail to see the criticism on my reply to you on THIS thread, seems you are getting a little thin skinned. I don't see where the tow haul or EB would have anything to do with his problem, but who knows until he gets it looked at.

DUDE, I just asked a simple question with ZERO comment if he used TH and EB. "TH and EB on all the time?"

Don't think that deserved your comment. "I know you seem to stress this, but yes the tow haul does hold the gears longer, but his shifting is something besides having the tow haul on. I don't see any change in shifting other then holding the"

 

[XJman]

Mine 2012 2500 does a similar thing and won’t kick down. My recent trip I had to keep kicking it out of 5th to keep it from lugging down below 1500rpm while pulling a pontoon up a hill. I did some research and saw a lot of complaints about similar things. I think it’s terrible shift logic.

 

[Cummins2014]

DUDE, I just asked a simple question with ZERO comment if he used TH and EB. "TH and EB on all the time?"

Don't think that deserved your comment. "I know you seem to stress this, but yes the tow haul does hold the gears longer, but his shifting is something besides having the tow haul on. I don't see any change in shifting other then holding the"

As said, grow some thicker skin, you are too sensitive.

 

[TJJEEPER]

Guys, take it off line PLEASE...

 

[Cummins2014]

Guys, take it off line PLEASE...

I tried, he likes the abuse public I guess

 

[Cummins2014]

Mine 2012 2500 does a similar thing and won’t kick down. My recent trip I had to keep kicking it out of 5th to keep it from lugging down below 1500rpm while pulling a pontoon up a hill. I did some research and saw a lot of complaints about similar things. I think it’s terrible shift logic.

Thats not right, it should not have to be done manually, pulling a grade with my fifth wheel, it will go as low a gear as needed, been many times in fourth on some steep grades. I don't leave it in cruise on the steeper grades, like to have the input on the throttle. Although it will shift down on cruise to fourth pulling a hill , I just don't let it.

Its sounds like you guys need to see the dealer, could be a flash or something, but that sure is not the norm. Granted its an issue.

 

[XJman]

Thats not right, it should not have to be done manually, pulling a grade with my fifth wheel, it will go as low a gear as needed, been many times in fourth on some steep grades. I don't leave it in cruise on the steeper grades, like to have the input on the throttle. Although it will shift down on cruise to fourth pulling a hill , I just don't let it.

Its sounds like you guys need to see the dealer, could be a flash or something, but that sure is not the norm. Granted its an issue.

Well, there are a ton of people out there with this same exact complaint. From older to brand new trucks.

You are correct in guessing it’s not right, probably off the game if you mean not purposeful.

 

[Cummins2014]

Well, there are a ton of people out there with this same exact complaint. From older to brand new trucks.

You are correct in guessing it’s not right, probably off the game if you mean not purposeful.

Ton of people okay, but what I am saying is its NOT the norm. No guessing involved ,something is wrong.

I see the motive about asking, it won't get fixed on here, but hopefully someone on here has had this corrected, and lead you guys in the right direction, thats all I was trying to say. Have these trucks been doing this since new, been into the dealer on warranty, off warranty , etc, etc ,etc, with no resolution ??????

 

[XJman]

From several of the posts that spanned over some years on several forums only a few had taken them to the dealer and were told it’s normal. If I had to jump out on a limb I would probably guess its emissions related somehow. Emissions are one of those throwing darts at the wall trying to see what keeps them down according to obsolete testing standards.