Gearing Options
Early Bronco 66-77
Transmission & Gear Page
Guide to 4WD Gearing
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Stick Trans Conversions
NV3550 5 Speed Conversion
NV4500 5 Speed Conversion
Auto Trans Conversions
C6 "Bad Boy" 3 speed automatic
AOD "Bad Boy" Automatic/Overdrive
700R4 "Bad Boy" Automatic Overdrive
NP435/T18/T19 "Granny Tranny" 4 speed co
Transfer
Case Options
Bronco Dana 20 transfer case
3.15 gearset for Bronco Dana 20
4.88 gearset for Bronco Dana 20
Atlas Transfer case
NP205 Transfer Case
"Ultimate" Compound transfer case gearing
Klune-V Extreme Underdrive
With Bronco Dana 20 Tcase
With Atlas Transfer case
With NP205 Transfer case
"Doubler" Dual transfer case systems
"Ultimate" transmission-compound transfer case systems
NV4500 - Klune-V - Atlas system
NV3550 - Klune-V - Bronco Dana 20 system
AOD - Klune-V Bronco Dana 20 system
700R4 - Klune-V NP205 system
1966-77 Early Bronco Vehicle Overview
The Early Bronco was manufactured by Ford from 1966-1977. They came with either a 6 cylinder or a small V8. early V8s were 289s, all others were 302. Up until 1973, the only transmission available was a 3 speed manual. In 1973 the C4 three speed automatic was offered as an option
All of these Broncos were supplied with a version of the Dana 20 transfer case. This case is NOT interchangeable with the Jeep Dana 20, it really should be considered a related but different unit. From 1966-1972 this case had a 1:1 (Direct) high range and a 2.46: 1 low range, and was shifted with a "T" handle shifter with a straight line shifting pattern 2H-4H-N-4L. From 1073-77 the transfer case had a 2.34: low range ratio. It was shifted by a shifter stick that operated in a "J" pattern.
The 3 speed manual is not supported in any of our conversions, we do not consider this transmission to be useful in any vehicle that is attempting top have optimal gearing options.
The C4 automatic is a decent trans, and as long as overdrive is not an objective, it can be quite satisfactory. It it is reliable in stock form with a stock 302 engine, and can be built to hold the power of most any Ford small block. High impact offers a "Bad Boy" buildup version of this transmission.
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Stick Transmission Conversion Options
General Info: Stick Trans conversion info
converting from auto to stick, etc.
NV3550 5 Speed Conversion
For general drivability considerations, this is the best stick-overdrive conversion for the vehicle. I will easily handle the power of the 302, and should be adequate for a mild 351. It has a 4.0 ratio first gear, which is very drivable. When used in conjunction with a Klune, it has all the gearing anyone needs
The NV4500 is a light truck transmission, conservatively
rested to hold 500 ft-lbs. We have seen them successfully used behind
engines producing over 800 ft lbs. The wider ratio (5.61 or 6.32 1st Gear)
is useful to get lower gearing off road when a Klune or Doubler is not
used. It is also the transmission of choice where one is expecting extreme
offroad abuse: In a vehicle the size of a Bronco, it should be pretty much
indestructible
NP435/T18/T19 "Granny Tranny" 4 speed conversions
These are the tried and true manual tranny upgrades for the Bronco. 4 speeds, no overdrive, drive it like a 3speed around town using gears 2-3-4. It does drive a bit like a truck, but the granny first of these trannies is real sweet in the rocks, especially if you don't have a Klune-V Underdrive or Doubler.
Automatic Transmission Conversion Options
General Info: Auto Trans Conversions
How to make an auto trans live, General overview converting from stick to auto, etc
C6 "Bad Boy" 3 speed automatic
A C6 is a very stout Ford 3 speed automatic. If you are building a rig that will have gobs of horsepower, want an automatic, and you do not need an overdrive, this trans is probably the way to go.
AOD "Bad Boy" Automatic/Overdrive Conversion
For use with a Ford small block V8, the "bad boy" version of this trans will provide reliable operation with overdrive capabilities both off road and on. It will comfortably handle engines up to around 400hp.
700R4 "Bad Boy" Automatic Overdrive Conversion
Installing a 700R4 "Bad Boy" in a Bronco is more costly that installing an AOD. The transmission itself is more expensive, plus you need an adapter to bolt the GM trans up to a Ford engine. The reasons to consider a 700R4: It has a 3.06 1st gear compared to the 2.40 1st gear of the AOD. We are also more comfortable building these for high HP use, there are more aftermarket parts available with which to further approach true "bulletproof" status. Another benefit is the electrical control of the torque converter lock up: It is possible to manual-lock the converter in gears 2,3 and OD. Then when climbin an extended hill, the converter stays locked and the tranny runs just as cool as if it were on level ground. And the converter can be un-locked in 3rd and OD - sometimes this is preferable.
Transfer Case Options
Stronger output shaft for the Bronco Dana 20
In most cases, the stock tail shaft holds up fine. If you have been having trouble with bending or breaking them, or know that you are building such a monster, I would either consider this upgrade, or swapping to a stronger Tcase (i.e. Atlas stronger, NP205 strongest).
3.15 gearset for Bronco Dana 20
Deeper low range gears for the Bronco Dana 20. When the budget is limited, this can be provide a relatively low-buck improvement in rock-crawling capability. Used with a Doubler, this gearset begins to approach "Ultimate" class capabilities.
Atlas Transfer case
Tougher
than a Bronco Dana 20, available with 3.0, 3.8, 4.3 and 5.0 gear ratios.
Fully synchronized gears allow shifting "on the fly". Twin stick
operation allows 2-lo operation, or FWD-lo operation for better maneuverability
NP205 Transfer Case
This transfer case was designed for 1 Ton trucks, and short of huge commercial cases, this is the last word in "Strong". It has the drawback of being large (It barely fits between the Bronco frame-rails when clocked in stock position. In order to clock it up, the frame needs to be notched and reinforced). Its other drawback is its meager low range gear ratio of only 1.96:1.
If you are building a horsepower "beast" with huge tires and plan to abuse it BAD, this is the case to choose. If the gear ratio is not enough, combine it with a Doubler or a Klune-V Extreme Underdrive. Both the Doubler and Klune-V Goliath are in the same league as to strength.
"Ultimate" Compound transfer case gearing
Benefits of having up to four different Tcase ranges to choose from are discussed in the "Ultimate" gearing section of the Guide to 4WD Gearing
The Klune Underdrive is the Premium such product.
With the Atlas, we usually use either the 3.8 or 4.3 ratio Atlas in conjunction with the 2.7 ratio Klune. This allows for a similar 4-range distribution of useful ratios.
With NP205 Transfer case
The 4:0 Klune coupled to the roughly 2:1 NP205 allows 1:1, 2:1, 4:1 and 8;1 compound Tcase ratios available. Use the 4:1 and 8:1 when rock crawling, use the Klune in direct (the power does not pass through the gears, only the shafts) with the 205 in "Lo" for the hammer down wheelin'
The 2,7 ratio "Goliath" Klune becomes the item of choice in cases where extreme duty trannies such as the C6 are required: The Goliath supports the larger output shaft diameter of these transmissions.
"Doubler" Dual transfer case systems
A Doubler uses the 1.96:1 ratio reduction unit from an NP203 Tcase, to "double" the ratio of the Tcase behind it. Doubler systems are available for Bronco Dana 20, NP205 and Atlas applications. A Doubler used with a 4.3 Atlas would qualify for "Ultimate" classification. Doubler systems can be very economical in cases where you already have some of the key parts of the system. The Adapters used from the trans and Tcase are all factory adapters, and are getting hard to find (people are buying them up to use in doublers). If you already have a C6 or NP435 with the adapter and an NP203 attached to it, you already have half of the system. Then you buy the Doubler adapter kit to the Tcase you want to use, and you're in. If you do not have these parts on hand and will have to buy it all, it starts to make more sense to just buy the Klune.
"Ultimate" transmission-compound transfer case systems
NV4500 - Klune-V - Atlas system
Stick application for the extreme multi-use rig, built to the hilt
NV3550 - Klune-V - Bronco Dana 20 system
This is the ultimate stick setup for a weekend warrior. Use a nice streetable torquey V8, really nice drivability in the trans ratios, overdrive, and with the Klune, all the gearing you could need going out on the weekend to run the Rubicon or the Hammers or Tellico.
AOD - Klune-V Bronco Dana 20 system
This is a real "Ultimate" Type system, all the benefits of an automatic with overdrive, plus all the gearing flexibility of a Klune.
700R4 - Klune-V NP205 system
Add the benefits of a 700R4, and the strength of a 205. Of course, Ford purists might cringe at the idea of a GM trans in there...
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