Attention: TDR Forum Junkies 
OK, no biggie, but three days from Hershey, PA area to near Terre Haute, IN, 715 miles.
Not mountains, but lots of hills and mostly interstates 76 & 70. Flatter in Indiana.
I've been retired and towing for 14 years, and for the last 5 years tow a 2007 Excel 28 RTW 5th wheel camper at 15,000 lbs. The last 12 years I towed with my 2002 6 speed! So I'm used to and expecting to manually shifting and I guess I'm treating my new 68RFE as a manual too. I suspect I'm driven to keep it in lockup and minimize torque converter heat. So keep that in mind as you read on and that I have a 3.42 rear end.
Here is what I learned and post here to learn more from your experiences
After a bunch of experimenting, I ended up driving with the Exhaust Brake and the Tow & Haul both on, as many of you have reported doing. Here is what I found: Note that I most always used manual shifting of the ERS (Electronic Range Select) control. (After reaching close to desired speed, I down-shifted from 'D' to '6th' gear... or lower if needed.) AND I used speed control for 95% of the time on this trip. I rarely exceed 60 (OK 65 around towns where the locals drivers and the speed limit encourage me to speed up! And getting a run at a hill.) After all I'm retired and trying to save fuel and sooth my nerves (and my wife's)!!!
1. The transmission (68RFE with 3.42 rear end) (Exhaust Brake with T&H on) seems to like 4th gear around 40-45 MPH, 5th around 50-55 MPH and WILL shift into 6th at 60+ if not climbing. (Don't shoot the messenger for the approximate speed ranges I observed... after all I was driving too!) But MY truck WILL enter 6th with the EB & T&H on under the right conditions. Only occasional I did have to 'trick' the transmission into 6th by turning T&H off, then back on again. I seem to recall some discussions on the boards that the T&H will lock out 6th gear. Not so for me... but the conditions have to be right. Eg around 60+ MPH and not much of a climb.
2. When in 6th at about 60 and I see a 'modest' grade coming (what ever that means...) I could play the old trucker game and increase the speed control and get a run at the hill. It would stay in 6th as long as the differential between the set point and the road speed was less than 3 MPH. I would watch this differential and manually drop the speed control set point, bit by bit by bit to keep it at 2 or less. Problem here is that the peak torque curve is about 1500 RPM, so I had to get a run at the hill to keep the RPMs up a bit. Realize that my goal here was to prevent the transmission from down shifting and stay in 6th!
3. Now if I was at 65 and a better torque point, it might pull the entire medium grade...
4. When I saw a 'steeper grade' and guessed that 6th would not hold up, I looked for the flat spot just before the beginning of the grade, and down shifted to 5th gear. My aim was to do this so the transmission SMOOTHLY went into 5th lock up with out any jar or jerk. Once in 5th, with the speed set anywhere between 55 and 65, it would smoothly power up the hill without more down shifting, running at 1500 RPM or higher. Now realize I wasn't in the Rockies yet! (But that's where we're heading!)
5. Braking: I was delighted to discover that with EB & TH on, when exiting from an interstate or what ever, it only took a very light , but continuous pressure on the brake peddle, for the transmission to automatically begin a series of automatic down shifts to reduce my speed... all the way down to 2nd. BTW it does appear the exhaust braking kicks off at about 20-25 MPH. Not like my old manual EB that I could use almost to stall! Sometimes on a country road, just letting off of the accelerator, caused the transmission to being to down shift.
6. Speed Control on a down-hill run will automatically down shift and/or use EB to maintain speed to about a maxim of about 2 MPH above the set point.
7. And of course, manually down shifting would activate the EB as expected if de-accelerating.
Tom
Not mountains, but lots of hills and mostly interstates 76 & 70. Flatter in Indiana.
I've been retired and towing for 14 years, and for the last 5 years tow a 2007 Excel 28 RTW 5th wheel camper at 15,000 lbs. The last 12 years I towed with my 2002 6 speed! So I'm used to and expecting to manually shifting and I guess I'm treating my new 68RFE as a manual too. I suspect I'm driven to keep it in lockup and minimize torque converter heat. So keep that in mind as you read on and that I have a 3.42 rear end.
Here is what I learned and post here to learn more from your experiences
After a bunch of experimenting, I ended up driving with the Exhaust Brake and the Tow & Haul both on, as many of you have reported doing. Here is what I found: Note that I most always used manual shifting of the ERS (Electronic Range Select) control. (After reaching close to desired speed, I down-shifted from 'D' to '6th' gear... or lower if needed.) AND I used speed control for 95% of the time on this trip. I rarely exceed 60 (OK 65 around towns where the locals drivers and the speed limit encourage me to speed up! And getting a run at a hill.) After all I'm retired and trying to save fuel and sooth my nerves (and my wife's)!!!
1. The transmission (68RFE with 3.42 rear end) (Exhaust Brake with T&H on) seems to like 4th gear around 40-45 MPH, 5th around 50-55 MPH and WILL shift into 6th at 60+ if not climbing. (Don't shoot the messenger for the approximate speed ranges I observed... after all I was driving too!) But MY truck WILL enter 6th with the EB & T&H on under the right conditions. Only occasional I did have to 'trick' the transmission into 6th by turning T&H off, then back on again. I seem to recall some discussions on the boards that the T&H will lock out 6th gear. Not so for me... but the conditions have to be right. Eg around 60+ MPH and not much of a climb.
2. When in 6th at about 60 and I see a 'modest' grade coming (what ever that means...) I could play the old trucker game and increase the speed control and get a run at the hill. It would stay in 6th as long as the differential between the set point and the road speed was less than 3 MPH. I would watch this differential and manually drop the speed control set point, bit by bit by bit to keep it at 2 or less. Problem here is that the peak torque curve is about 1500 RPM, so I had to get a run at the hill to keep the RPMs up a bit. Realize that my goal here was to prevent the transmission from down shifting and stay in 6th!
3. Now if I was at 65 and a better torque point, it might pull the entire medium grade...
4. When I saw a 'steeper grade' and guessed that 6th would not hold up, I looked for the flat spot just before the beginning of the grade, and down shifted to 5th gear. My aim was to do this so the transmission SMOOTHLY went into 5th lock up with out any jar or jerk. Once in 5th, with the speed set anywhere between 55 and 65, it would smoothly power up the hill without more down shifting, running at 1500 RPM or higher. Now realize I wasn't in the Rockies yet! (But that's where we're heading!)
5. Braking: I was delighted to discover that with EB & TH on, when exiting from an interstate or what ever, it only took a very light , but continuous pressure on the brake peddle, for the transmission to automatically begin a series of automatic down shifts to reduce my speed... all the way down to 2nd. BTW it does appear the exhaust braking kicks off at about 20-25 MPH. Not like my old manual EB that I could use almost to stall! Sometimes on a country road, just letting off of the accelerator, caused the transmission to being to down shift.
6. Speed Control on a down-hill run will automatically down shift and/or use EB to maintain speed to about a maxim of about 2 MPH above the set point.
7. And of course, manually down shifting would activate the EB as expected if de-accelerating.
Tom
