Towing Hi RPM problem

[SF Jakey]

I posted this on the drivetrain forum and didn't get a response, so I'm trying here.
I've got a 02 2500 4x4 ccsb D/A w/285's and tow a boat that is about 10,500 on the trailer. When in tow haul mode, the tranny likes to stay out of OD, so I'm turning hi rpms to go 65. Is there any modification to make it stay in OD and use the existing torque in the motor to travel at 65. I'm stuck going 50-55 to keep the rpm's low enough, and with the high rpms, the fuel consumption really sucks, like 7-8 mpg. I've thought about the juice box, but I don't know if it helps with the shifting. Are there any tranny upgrades to keep it locked up in 5th? On long flat stretches, I take it out of tow/haul because I seem to be able to control the shifting better, am I frying the tranny doing this? I also watch the trans temp, and it never goes over 200. Any suggestions?

[Inspector]

I tow about 14000lbs. Before I juiced I could tow in OD. I would check to make sure that your trailer brakes aren't dragging. Maybe have the dealer check for upgrades to your PCM or TCM. Doesn't sound right to me. 10500 is pretty light weight for these trucks.
Denny

[OC_DMAX]

I am wondering if part of your troubles are the 285 tires. I have no trouble with 10K pound loads (travel trailer plus load in bed) that are higher profile than a boat. This is with factory ECM programming.

Anyway, the Juice/Attitude (run on level 1) will definetly help your situation. From a towing perspective, the difference between night and day. Make sure you hook up the Pyro. It will stay in 5th much better and drag down in rpm instead of shifting into 4th so quickly.

When in Tow/Haul, the shift points are raised and the torque converter gets locked in gears 2-5. Plus, there is a more aggressive use of the grade braking feature. As long as you are at freeway speeds and in 5th gear, there will be no problem not using Tow/Haul (torque converter is locked). However, if your speed slows down (like winding through a mountain road or city driving) and you end up in other gears, you could overheat the tranny fluid. So keep an eye on it or engage the Tow/Haul feature.

[Kennedy]

A box like the Juice will help with the transmission by allowing you to make more power with less pedal position therfore running with earlier upshifts, and delayed downshifts.


Like OC said though, the tires do mess with the shift points. The shift speeds are dictated by the transmission output shaft speed so if you mess with the final ratio by say 8%, your mph for each action will be increased by the same 8%.


I've stuck with 265's on my trucks, and find that they tow very nicely. My lone bad towing experience was with a 17k stack of trailers standing over 13' high, and running an old style psi box. Since the pulse boxes have been released, towing capability has been greatly enhanced for me:

http://www.kennedydiesel.com/photogal/images/Trailer%20stack.jpg

[BlackMax 2001]

I pull a 5K (loaded) horse trailer. I always pull in the Tow/Haul mode. Mine never hits 5th gear until I reach 60-65 mph, but when it hits 5th, it rarely downshifts. And I tow in WV. I have had mine since 8/2001 and I still grin every time I drive it.

[BozDMAX]

I pull a 14K+ trailer quite often, in TOW/HAUL and notice that it will shift into OD at about 58MPH (stock tires - 215's) and then settle into a nice 1700 RPM cruise and 12.5-13 MPG.

Since I am retired and have more time than money, it works for me. I think the torque curve peaks around 1800 RPM anyway, so I have plenty of passing power when I need it to stay out of people's way. Drive much faster and the aerodynamics will really drop the mileage.

Can't explain why yours won't shift at 60-65 but my chip may have something to do with it. Where does it shift when you are NOT towing?

[SF Jakey]

When I'm not towing, it shifts and locks up fine. It's just when I try to tow over 60 that it tends to downshift and stay there. With the 285's I think 60 is more like 63or 64 though. The boat is a very tall pilot house style offshore fishing boat, my profile is actually taller than most travel trailers so I have quite a bit of wind resistance. I'd like to be able to cruise @70 without turning 3000 rpm, that's why I ask about mods. Sounds like the juice may be in order

[OC_DMAX]

I know you'll be happy towing with the Juice on Level 1. Report back on what eventually happens.

[lburks]

Do a search on "OD lockout switch".

My 02 shifting problems were solved.

Lock out is not available on the 01 and 02, you have to install a switch. 03 and later came on the T/H switch.

Happy towing

[SF Jakey]

I'm actually looking for a way to keep the truck in 5th, not lock it out. 2000 rpm is plenty of torque to hold that gear, I see no need to downshift. Is there a way to "lock in" 5th gear?

[OC_DMAX]

There is no convenient way to hold the Allison in 5th. The Juice in Level 1/2 will hold 5th gear a lot longer, but it will eventually downshift.

Kennedy in his post above presented a good explanation of why the Juice hold 5th gear longer. The Allison controller is looking at throttle position, gear selection and vehicle speed (transmission output shaft rotation rate) to determine how to control the transmission. For a given throttle position, the Juice applies more fuel than the stock ECM programming, thus more torque. However, the transmission does not know this. The end result is the engine pulls a lot harder before a downshift is commanded by the transmission controller. Which is exactly what you want for your towing application.

[Diesel Crat]

Have experienced same problem in Tow/Haul with my 02 4-door short bed.

Even after reaching 65-70 mph and easing off the pedal she still won't upshift on the flat.

Never had a problem until this winter towing in the cold. Motor and tranny were fully warmed up at time of incident. Pulling a 7000 lb v-nose at 9'-10' tall which should be a walk in the park for this truck. Truck is bone stock...

Has there been any issues with the TPS units?