Overdrive

[Sterling]

Have I missed something here? The original poster was asking about the overdrive switch on his '91 F-150. Why would he care how the transmission works on an '02 Sonoma, '03 Corolla, or a '99 CRV?

[Bodin]

soo... currently I turn the OD off in the city(50kph-60kph) and when I hit the highway(90kph-100kph) I turn on the OD correct?

[barrie1]

Yes. The owners manuel will give you the best answer of all on your model. The early designs were all different from each other so read up on the one you own.  

[neil]

A lot of import cars used to have a "sport/eco" button associated with the tranny.  These are rare now but this used to change the shift points.  I suppose your vehicle has combined the OD button to this function.  
Chryler and Hyundai I know of as fact employ fuzzy logic, which makes the button redundant.  The fuzzy logic adapts to your driving style, if you are agressive the computer adapts the shift points to your driving style after a few minutes.

Sterling is correct that the OD button simply does not allow the vehicle to enter top (4 or 5) gear.  It does not change ratios, but may put the tranny into a sport mode.  Certainly not a factor on a 91 Ford.

Most imports today, and GM products have full selectability on the shift lever.  GM's read in the indicator P R N OD (D WITH A CIRCLE) 3 2 1
Fords of this vintage would have read P R N D 2 1, "D" being either 3 or 4 depending on the OD button selection.  Dodge read P R N D 2 L.  Now for Hyundai product, the Accent's 4 speed auto reads P R N D 2 1, with an OD button, and the Elantra has P R N D 3 2 1, and no button.

Barrie mentioned the early 4 speed autos at GM had problems.  My brother had an S-15 with this transmission, and the problem.  This was very acute and noticeable where at normal in-town speed 50-60 km the tranny would very noticeably hunt 3-4-3-4-3-4-3 constantly.  I'd say pay attention to your vehicle.  If at speeds you normally drive you find your tranny hunting, shut the OD off.  If it doesn't leave it on, you'll save fuel.  Common sense should prevail eh?

[Bodin]

Thanks Barrie, Neil and others for clearing that up. Before I always thought that with the OD off I would save gas. Now I am just gonna leave it on because it has never had any trouble with shifting between 3rd and 4th.

Thanks again,
Bodin

[ovr50]

Actually in most cases, with OD on you will be more gas efficient. With modern electronic trannys, just leave it in OD and let the tranny decide. The only exceptions would be towing or maybe very steep downslopes. On my RAV, the OD is 4th gear and with it off, the tranny will be in 3rd and not shift into 4th. I'm late in here so this is probably old news.