rplst8 posted:I don't know if it helps you 2R guys, but put in a reservation for 2 W&LE 3R SD40-2 in 3R. I found this thread very helpful in learning about the other SD40-2 models out there. I'm glad I didn't buy any of them. One question though, what exactly is a tank drive?
A tank drive is a common name for a horizontally mounted motor with a worm gear that powers all axles. The Sunset / 3rd Rail drive is a roughly center mounted can motor in the body with a geared belt similar to some timing belts in cars that connects to the worm gear inside the fuel tank.
From a performance standpoint the drive has more torque than the vertically mounted "China drive" as it is commonly referred to. Atlas has used a tank drive in the AEM7 and the early SW units. My AEM7 is an outstanding puller for its size. Also slow speed performance without command is a little better and with command the tank drive can run right at 1 smph.
From an aesthetic standpoint the worm being exposed visually in a few spots at the level of the fuel tank can be distracting on locomotive with smaller tanks. The benefit it that it does allow for a complete cab interior with control stands and other interior features.
Hope that helps. I should take some photos.
