Move a transmission gear to the transfer case?

[John_parkeriv]

So I'm wanting to put a fourth gear in my bronco as an overdrive, but I also want to keep my three-on-the-tree shifter. Would it be feasible to move my reverse gear to the transfer case? Maybe replacing the 4-High gear set?

 

[73azbronco]

anything is possible, what you suggest is highly unlikely.

 

[Broncobowsher]

No, not possible.

It could be done, but the skills needed to do it would be that of engineering a brand new transmission and transfer case. And if you had those skills, you wouldn't be asking the question.

There is a 4-speed version of a toploader 4-speed, that does have an overdrive. It is done by making it a 3-speed, flipping the linkage on the 3-4 shift. So the direct drive is now 3rd gear (instead of 4th) and what was 3rd gear is now setup as an overdrive 4th gear. And the ratio for 2nd gear is changed to make the spacing correct. 70's Ford engineering taking what they had and re-working it into an overdrive transmission without too much work. I recall the Econoline version is the better one, has a bearing for overdrive instead of a bushing used in cars.

At this point they are a bit difficult to find. Find a 40+ year old transmission that is usable, or for that matter even rebuildable. And you would need that exact transmission case as it has a bulge in the case to fit the larger overdrive gear.

Realistically, there are plenty of better 5-speed options that are way more available.

Now the other question, can you even take an overdrive? What axle gears do you have now? What size tire? Even what engine? Good chance you don't have enough gearing to use an overdrive. Are you thinking you need an overdrive based on engine sound?

 

[John_parkeriv]

Now the other question, can you even take an overdrive? What axle gears do you have now? What size tire? Even what engine? Good chance you don't have enough gearing to use an overdrive. Are you thinking you need an overdrive based on engine sound?

I think it's running the original rear gears, so probably a set of 4.11s. OEM tire size, 235/75R15, and the ol' 170 straight six. It just seem to rev high at about 55-60. The point is for more of a highway gear, even if I can't accelerate any faster. It would make sense to me that it'd be better on the engine (and fuel economy) to run an overdrive.

Of course if it'd just be easier to swap the tranny, I could. I just wanted to keep that original 3 speed look.

 

[Broncobowsher]

Lack of engine size is more of a problem. The 4.11 gears where the fix. Highly doubt that an overdrive will do you any good. To run an overdrive you need more torque at lower RPMs.

Here is a little math. Some numbers stretched a little just to make the math easier.
Lets say you find a .75 overdrive. That is a fairly normal ratio. If the engine was turning 4000 RPM without overdrive and you shift into overdrive it will drop to 3000 RPM. But you would need 33% more torque at that 3000 RPM. Why 33% and not 25%? 4/3rds. Output is at 4000 RPM (driveshaft) but input is 3000 RPM (crankshaft). 133% input to get 100% output. The 170 just doesn't have the torque capacity.

Don't confuse thinking that driving at 3000 RPM currently it feels OK, that higher speed has more wind drag. So you won't have the same feel at a higher speed at that same 3000 RPM.

Now my 3000 and 4000 numbers are probably a bit off. But they get the point across. You can scale the numbers however you like. Multiply all my numbers by 0.9 or whatever it takes to correct to your actual numbers.

As for a column shift 4-speed, it has been done. Gets funky as you have to add a separate divorced lever somewhere else to engage reverse. The toploaders are a different length than the 6-cylinder transmissions, so the transfer case would have to move as well. And that means resizing both driveshafts.

 

[John_parkeriv]

Lack of engine size is more of a problem. The 4.11 gears where the fix. Highly doubt that an overdrive will do you any good. To run an overdrive you need more torque at lower RPMs.

Here is a little math. Some numbers stretched a little just to make the math easier.
Lets say you find a .75 overdrive. That is a fairly normal ratio. If the engine was turning 4000 RPM without overdrive and you shift into overdrive it will drop to 3000 RPM. But you would need 33% more torque at that 3000 RPM. Why 33% and not 25%? 4/3rds. Output is at 4000 RPM (driveshaft) but input is 3000 RPM (crankshaft). 133% input to get 100% output. The 170 just doesn't have the torque capacity.

Don't confuse thinking that driving at 3000 RPM currently it feels OK, that higher speed has more wind drag. So you won't have the same feel at a higher speed at that same 3000 RPM.

Now my 3000 and 4000 numbers are probably a bit off. But they get the point across. You can scale the numbers however you like. Multiply all my numbers by 0.9 or whatever it takes to correct to your actual numbers.

As for a column shift 4-speed, it has been done. Gets funky as you have to add a separate divorced lever somewhere else to engage reverse. The toploaders are a different length than the 6-cylinder transmissions, so the transfer case would have to move as well. And that means resizing both driveshafts.

Yeah, that seems like more effort than it's worth. Thanks for letting me know before I tore my tranny apart!