My truck is a bone stock 6.7L auto with the exception of an aftermarket stereo. I've been doing some heavy driving the past couple of days in the Northern Arizona/Southern Utah area (no towing) where temps are between 25 degrees and 40 degrees farenheight and I average 75-80mph while driving. I noticed the other day that when I was picking up speed, my truck didn't shift into 6th gear for a while. I was at about 2300-2400rpm driving around 60-65 mph where normally, it would be somewhere around 1500rpm at that speed. It would drive like this for about 2 minutes, and then it would shift. I also noticed that when the temperature needle reached normal temp, thats when it would shift into 6th gear. I checked the transmission fluid level later at a gas station and saw that it was normal. Is this shifting behavior normal?

BTW, driving through this beautiful countryside, I noticed that approximately 7 out of 10 trucks are DODGES!!! Awesome!

 

Tranny wont shift into 5th or 6th until it reaches operating temp, its designed to do that.

 

Blake.Clark, thanks for the quick reply. I find that pretty interesting. I don't understand why it would be designed that way. This is my first diesel and I'm learning a whole lot about the Cummins (especially through this site). What's the rationale for not shifting into 6th gear until the engine reaches operating temp??

 

Sorry for the misunderstanding, it wont shift into the higher gears until the tranmission fluid reaches a suitable operating temp, not engine temp.

 

Not sure exactly why, but this is not just for diesel trucks. Many auto transmissions on different vehicles will delay shifting until it is warmed up enough. I think it has to do with the high viscosity of the cold fluid.

 

Case Number K00053751
Vehicle Issue No 5-6 Upshift when Cold;Trans will not shift beyond 5th gear, and TCC will not engage, until trans warms up. Monitor the target gear, target TCC state, and trans sump temperature while operating the vehicle. If the target gear does not advance beyond 5th gear, and the target TCC state remains as "Unlock," then the transmission controller is deliberately inhibiting TCC engagement (and 6th gear). This is probably because the trans sump temperature is 55°F or below. See detailed explanation below.
System or Component Transmission / Transfer Case Engagement / Shifting Issues,Upshift / Downshift Issues,Late Upshift / Upshift is Delayed,No Shift / Will not Shift Up or Down;Customer Concern (No DTCs);Group 21 - Transmission / Transfer Case / Power Transfer Unit ( AWD );Cold Start (After 8 hour Soak),During Warm Up;6th Gear,5-6 Upshift;Higher Speed / Greater than 50 MPH ( 80 KPH );Yes - Intermittent,Yes - Continuously
Recommendation No 5-6 upshift when cold is NORMAL for the 68RFE transmission. Engagement of the torque converter clutch (TCC) is inhibited when trans sump temperature is below 55°F or engine coolant temperature is below 120°F. Normally, the transmission engages the TCC in 5th gear, and the TCC remains engaged during the 5-6 upshift. The 5-6 upshift will not occur until the TCC has engaged. Therefore, when TCC engagement is inhibited (due to cold temperatures), the 5-6 upshift is also inhibited. Once the trans sump temperature exceeds 55°F, and the engine coolant temperature reaches 120°F, normal TCC engagement (and 5-6 upshifts) should occur.

Modification Date 01/22/08 3:55 PM

 

Awesome! As long as it's normal that's all I need to know. At least I know to warm up the truck for a little bit and not to try to exceed 60mph until the gears shift. Thanks for the info!

 

My old Dakota would do the same thing. It was a 92. It wouldn't shift into second as soon cold as at op temp.