I have a 91 F150 I-6 with a 5 speed trans. The gears have begun grinding pretty bad, especially when you downshift. I'm not extremely familiar with transmission problems but I think my best bet will be to replace this one.

I have considered replacing the manual trans with an automatic for a couple of reasons: 1. although I LOVE a manual trans, I plan to sell this truck and I am thinking that it will probably sell faster and for more money if it is an automatic. and 2. I sometimes borrow my moms van for family trips (about twice a month) and she does not know how nor willing to learn to drive either of my manual trans equipped vehicles, so while I have this truck, until it sells, it would be very helpful for her to be able to have something to drive when I borrow her van. and putting an automatic in my Merkur XR4Ti which I have put a T5 in is OUT of the question...

So my questions to y'all are these:

How much trouble is it to swap an auto into this truck in place of the 5 speed? I swapped a C3 out of my Merkur and put a T5 in and it wasn't difficult at all. but in this truck will there be any electrical / computer issues?

What auto trans would you recommend?

If I decide to stay with a manual trans. which one would you recommend?

Thanks for all the input!
Doug

 

You have a few options to choose from.

With a manual trans, there's nothing to worry about with the computer.

So, you can put in either a C6 or an AOD. Both are vacuum operated, so it's just a matter of removing the manual and putting the auto in. The C6 is tried and true and tough as nails. I've heard multiple opinions on the AOD, but ultimately don't really know what the final verdict is, but have heard it's a good transmission.
Either way, it's overdrive, which always helps with gas mileage.

There's also the E4OD, but that's computer operated, so that would need to be addressed.

For manual transmissions, a replacement with the same you have (Mazda M5OD), or the ZF5. The ZF5 is a lot more robust, but if you have a 4x4, it can be rather expensive since they're sought after.

Then, there's always just a good ol' NP-435. You'd lose overdrive, but it's a tank of a transmission.


One thing to keep in mind is that transmissions are different lengths, so if you get a longer or shorter one, you'll need to move your transmission crossmember and/or lengthen/shorten your driveshafts.

 

Swapping to an auto would also mean changing the pedal set as well as a steering column with a gear selector. Your state may require a shift indicator as well.

 

Can also use a floor shift with an automatic C6.
"Speedway" has a kit that bolts directly to the automatic transmission for a floor shift option.
Have a 300/C6 laying in the dirt and the transmission kickdown linkage mechanism is rather crude on the 300 engine.
Would opt for a cable operated kickdown rather than stock style linkage.
The stock linkage style also requires a plate with adjustment screw on the carburetor throttle shaft to activate the kickdown linkage.

Another option is the manual 3 speed or 4 speed Ford top loader style with cast iron case and cast iron bell housing.

Would guess that the 5 speed manual in the 91 is a Mazada M5R2.
One problem with the Mazda M5R2 is the dimension from the drive center line to the top of the shift tower is much greater than the T18 or T19 tower shift manuals.
So ,on an older body style retor fit conversion a large cutout hole in the floor is required to accomodate the shift tower. The internal hydraulic clutch throwout bearing is a plus.

Currently replacing 390/C6 with a 300/ Ford 4 speed top loader with hurst shifter with CI bellhousing and internal hydraulic clutch throwout bearing release.