What exactly is the purpose of the overdrive off button on dash ? I can't understand why OD would be selected off, maybe for towing ??

 

Frequent shifting is hard on an auto trans(generates heat) so any situation where you find it is constantly shifting up and down from 3rd to 4th for whatever reason you can lock out OD with the button. Some of these trucks were equipped with high(numerically low) axle gear ratios and that combined with relatively weak motors can create a situation where the trans is constantly hunting at highway speeds.

 

Thanks that explains allot

 

The AOD shift dial quadrant: P R N 0 D 2 1 / AOD introduced initially in 1980 LTD/Grand Marquis/Lincoln 302, 1981 F100/150 & E100/150 300/302.

There was no lock out button, owners manuals said to use 0, didn't mention a peep about not towing in 0. Car/truck salesmen were (as usual) clueless, told their customers the same thing.

So people drove in 0 instead of in D in heavy stop and go traffic. The constant shifting up/down - in/out of O/D fried the AOD's guts, and it didn't take too long for this to occur, either.

People towed in 0 instead of in D .. the AOD's guts fried faster than driving in heavy stop and go traffic.

IMO, the AOD was the 2nd worst A/T that FoMoCo foisted on mankind. The A4LD used in Rangers and Bronco II's, was even worse.

 

Yep. Not sure how it's predecessor (C3) or the newer variants of it (5R55S) are but the A4LD itself is the worst transmission I ever owned!