Mostly due to operator error. Using toggle switches or any configuration other than stock makes it a one person driver.
By forgetting to disengage the solenoid and starting off with it engaged puts an undue load on the overdrive components.
Think about moving a two ton truck from a dead stop with three one inch pinion gears. That's the size of the pinions that make up the planetary. The same situation applies to the teeth on the sun gear & control plate.
Also, when shifting into reverse the overdrive is disengaged in normal operations. If it is possible for it to become engaged in reverse
it will destroy a whole bunch of expensive components.
I see the referenced diagram uses the governor but quite frankly I don't see the need for 2 power sources to complicate something that is relatively simple.
A guy called me a while back and he had installed an OD with the aforementioned wiring configuration. He could not get it to work correctly.
I offered a couple of suggestions to see if I could help him but I'm not sure if he ever got it to work.
Fred
