Ford 150 Over Drive

[nickcrowhurst]

I'll make a couple of points that relate to the overdrive issue:

1. If you ride a pedal cycle with gears up a hill, and you are in too high a gear, you will feel a huge strain in your legs. Change down, pedal faster and you will feel less strain. That is a rough and non-scientific analogy which shows the extra strain you are putting on a transmission by risking using the overdrive.

2.By definition, in overdrive, the output drive from the gearbox is turning faster than the engine. If you strip down and dismantle a simple manual gear box, you will see that in top gear (not overdrive), the engine is coupled solidly and directly to the prop shaft connected to the back of the gearbox. There are no intermediate toothed gears which can break, or whose bearings can fail. When overdrive is engaged, the power is transferred across to a parallel shaft in the gearbox. The receiving gear has less teeth than the transmitting gear, so it rotates more quickly, and at the other end of this shaft, the drive is transferred back to the output shaft by another pair of meshed gears. You can see that in top gear, there is far less to fail. Overdrive units are inherently weaker because they introduce a complex path for the power, and this path is weaker than the direct physical connection in top gear. That has been the case in the simple manual gearboxes I have overhauled.

Those two reasons cause me to avoid towing in overdrive.
Nick.