RFCRD wrote:
Cowcatcher wrote:
Seriously I would like it too when I start towing. When I see some here talking about towing with the OD locked out all the time I am wondering what that is doing at 65/70 MPH that they are also posting. I would likely only tow in OD until I got into hils then I would be turning it off and on not just locking it out for the duration.
If you want to get really technical with this stuff, start looking at the performance chart for this engine, final drive ratio, and transmission gear ratios (1:1, 0.75:1, and 0.67:1). Detroit Diesel/Allison does the exact same thing in a heavy bus application. Ratios are spaced perfectly to provide optimal efficiency (fuel economy) at 45, 55, and 65 mph (3rd, 4th, 5th gears) and optimal performance (max usable power) at 55, 65, and 75 mph (3rd, 4th, 5th gears). The efficiency peak of one gear is the performance peak of the next lower gear. The short of it is that if you are towing under load @ 65 mph with any amount of hills, you want it locked into 4th or it will go likely go "hunting." The little bump in RPM will also keep your fluids moving and fan turning faster to prevent the overheating some are reporting.
Driving this combination in a bus application @ 55-60 mpg (urban expressway or rolling hills), you actually have to manually lock-out the deep overdrive or the transmission will be contantly "hunting" for a gear which will trash a $15K Allison in short order. Starting to sound familliar???
Boy, does it. That is why I would like more control over my CRD tranny. Of course, I could always lock out the OD and then never drive over 55.
Even with the new autoshift tranny setups in some semi's, I like to lock the shifter then hit the button when I want to shift up when in certain situations. The programming for them is along the same line as for the full auto trannys. Sometimes, it is not always a good thing to have the equipment, be it Semi or CRD, to take over too much from the driver. Oh well, welcome to the 21st century.