Need Overdrive Trans - Any such Beast???

[GYShah]

Thanks guys!
I'm getting a solid 11.5 mpg in town which is 90 percent of my driving
And I'm ok with that
(if I wasn't, I'd drive a Prius like my dad, lol)
I was asking because I was wondering whats going to happen when I go from 3.5 to 4.11 and from 33" MTs to 35" ATs

 

[Broncobowsher]

I got 16 once...I had the bronco stripped down hardly anything inside,no doors,no top, and we even strapped it down on a trailer!! Finially we lashed the trailer to my 96powerstroke with a gear vender overdrive....Then I reached 17 mpg and imedate success!!

I like it...;D

You might be able to hit 18 if you start with a full tank on top of a mountain and fill upagain at the bottom.

 

[broncnaz]

Things will probably stay about the same with those changes. So you should maintain current power level RPM's will go up slightly but on the lowend take off should improve a little so overall you may gain a little especailly driving in town.

 

[markperry]

Thanks guys!
I'm getting a solid 11.5 mpg in town which is 90 percent of my driving
And I'm ok with that
(if I wasn't, I'd drive a Prius like my dad, lol)
I was asking because I was wondering whats going to happen when I go from 3.5 to 4.11 and from 33" MTs to 35" ATs

You may already know this but when you change gearing from a 3.5 in the front to a 4.09 to match the 4.11 in the rear, it takes a different carrier, or a thicker ring gear. I learned the hard way!

 

[bighoss22r]

I will chime in,
I am currently running a 289- 3 speed-3.50 gears and 31"tires, I get a consistant 14.5 mpg on the freeway @65-70mph. That is only freeway driving, no in town stuff. 80 miles round trip to work. I will be putting in an AOD at the end of January. I am hoping to increase to 17ish mpg with the OD. But i could be completely wrong about that, only time will tell
I am only gonna be into the tranny for about $550 so I figure it will take less than a year to pay for itself plus it will make for a much more comfortable and quieter commute.

 

[broncnaz]

Most likely you wont gain squat with the AOD tranny swap alone. Just due to your gearing and tire size. As the engine will be lugging to push the bronco when in OD the engine needs to be in its torque range 289's are not lowend torque monsters they need to rev to maintain the torque. Also when in OD it takes more power to keep the tires turning than it does with 1-1 gearing if the engine doesnt have that power it lug. If you had 4.10 gearing and 31in tires you might see a actual gain. Also any speed below that 65 mph mark and the tranny may constantly shift out of OD.
I could be a little off in the math but swapping in a OD tranny would be like going from 31in tires to 40 in tires without regearing the axles. of course this is only when you are in OD but the effect is the same a almost 30% reduction in RPM's it just takes more to keep the vehicle moving.

There's a reason that OD equipped trucks have the gearing and tire sizes they do from the factory as its usally very close to the optimum setup. Even going back to the non OD days gearing and tire size was based upon the engines torque range and where it could loaf and not struggle while cruizing down the road.

 

[DirtDonk]

...Do you have a wind tunnel, Paul?
I think we need to put a bronco in a wind tunnel

Definitely!
Don't have one myself unfortunately, but I'm just down the road from a huge one at Ames Research Center at Moffett Field.
A REALLY big one too.

Wonder if anyone here has any connections to get one in for testing?
Of course, we can probably just do some real-world testing and find out most of what we need to know, but it's fun to think about.

Paul

 

[Broncobowsher]

There was an article in Hot Rod 4-5 years back about wind tunnel rental. It was more of a Bonneville thing, but there are tunnels that you can rent. Makes dyno time look cheap. The ones we rent at work are all in Michigan.

 

[nvrstuk]

So if the coefficient of drag formula that some use for racing at Bonneville says that it takes almost 9 times as much horsepower to drive a Bronco at the same speed as a sports car computes to pretty much the same thing as saying that a Bronco looks like a BRICK WALL in a wind tunnel. ;D

The bigger and wider the tires, the more lift, the bigger the wall...

 

[GYShah]

Still, it would be cool to plot out a curve of drag vs speed for different setups (lift, tires, etc.) so you could know where the "brick" hits the "wall"
I'm pretty certain Ford never did any wind tunnel tests on an off road sports vehicle in the pre-gas crunch era...

 

[Broncobowsher]

So if the coefficient of drag formula that some use for racing at Bonneville says that it takes almost 9 times as much horsepower to drive a Bronco at the same speed as a sports car computes to pretty much the same thing as saying that a Bronco looks like a BRICK WALL in a wind tunnel. ;D

The bigger and wider the tires, the more lift, the bigger the wall...

I actually think the brick wall would be more aerodynamic. That's not a joke, I really do feel a brick wall would have less drag then the typical lifted Bronco.

 

[broncnaz]

Still, it would be cool to plot out a curve of drag vs speed for different setups (lift, tires, etc.) so you could know where the "brick" hits the "wall"
I'm pretty certain Ford never did any wind tunnel tests on an off road sports vehicle in the pre-gas crunch era...

Probably because its pointless to do so as the brick kinda hits the wall in stock form anything else you do just makes it worse. You dont do wind tunnel testing on vehicles that are not meant for economy or speed. You basically know the outcome on any lifted vehicle. kinda like testing a piece of plywood then adding more wood to the edges drag just increases.
Now if your a rich eccentric person with nothing better to do go for it.
I'd probably venture to guess that few production vehicles actually see any wind tunnel testing.

 

[Bronk]

This will be my next major project , I don't know if anyone brought this one up yet but if your not a rock crawler it maybe what your looking for.

http://classicbroncos.com/tech/nv-3550-install

 

[Idaho Slim]

This will be my next major project , I don't know if anyone brought this one up yet but if your not a rock crawler it maybe what your looking for.

http://classicbroncos.com/tech/nv-3550-install

That is very VERY interesting ............. I see wherer they address being able to handle the added power of my built 351. That might be my only resistance to doing this. ;D;D Thank you for the link!!

 

[Bronk]

I have seen other posts with them bolted up to 351's and they seem pretty happy with the set up, I'm thinking 400 hp would be handled , these are a truck tranny so they where made to take some torque.

on whole other note one of my buddies has a 3 spd with a electric od tranny out of a 78 ford truck that would be a real easy swap. it looks like the typical ford three speed with a od attached.

 

[broncnaz]

.

on whole other note one of my buddies has a 3 spd with a electric od tranny out of a 78 ford truck that would be a real easy swap. it looks like the typical ford three speed with a od attached.

That tranny is probably way older than the late 70's mostly likely early 50's to early 60's. to the best of my knowledge there were no electric OD 3speeds in the 70's. in the 70's they did have what is called a 4sp OD and many call it a 3sp with OD it looks very similar to the toploader 4speed and stock 3sp and can be swapped in easily.
No sure how easy it would be to swap in a electric OD tranny you may run into issues with the adapter housing. Still it would be a interesting swap if it could be done easily.

 

[Bronk]

That tranny is probably way older than the late 70's mostly likely early 50's to early 60's. to the best of my knowledge there were no electric OD 3speeds in the 70's. in the 70's they did have what is called a 4sp OD and many call it a 3sp with OD it looks very similar to the toploader 4speed and stock 3sp and can be swapped in easily.
No sure how easy it would be to swap in a electric OD tranny you may run into issues with the adapter housing. Still it would be a interesting swap if it could be done easily.

So is the 4sp OD electric or mechaniclly shifted ?

 

[broncnaz]

Mechanically shifted. Basically looks exactly like the stock bronco 3sp with one extra shift lever or a toploader 4speed tranny but has a OD gear. They also have a lower first gear and worse spacing between the other gears.

 

[Bronk]

Thanks for the info Now i'll have to go there and see what he really has.

and after hearing that they had worse spacing between gears . that would be a BiG downfall of that tranny

 

[broncnaz]

Well you figure lower first gear usually 3.25-1 which is good 2nd is is about the same as 2nd in a 3sp and 3rd is 1-1 leaving 4th as a OD So that kinda leaves a wide gap between 2-3. kinda why a lot of people dont like the gearing in 3speeds as it is.
Some of the 4sd OD in trucks had a top mounted shifter or a tail housing mounted shift while they still look like the orginal toploaders they wont have levers out the side.