Converting Your Bronco II From 2WD To 4WD – Overview

 

Almost all 2WD Bronco II’s came with a BW1359 dummy transfer case. This means you probably already have a 4WD transmission and the rear driveshaft is already the proper length. 

To Do This Conversion, You’ll Need:

1) A transfer case (Manual or Electric). 

a) If you use a manual transfer case, you’ll need the transfer case shifter, linkage and bolts (you must get the correct linkage to fit the transmission you’re using), shifter boot and floor plates, and harness that runs from the plug on the driver side inner fender to the transfer case. 

b) If using an electric transfer case, you’ll need the main harness behind the dash, harness for the transfer case, 4WD shift switch for the dash and the electric shift control module that mounts behind the drivers seat interior panel. Make sure you get the harness and grommet that goes through the drivers floor board.

2) You’ll need a transfer case to transmission gasket. 

a) If using a manual transfer case, inspect the bushing for the shifter linkage. If it’s wore out, now would be the time to replace it. You’ll have to pick one up from your local Ford parts counter.

3) If you plan on keeping the stock suspension and not lift it, you’ll need the mounting bracket for the passenger side axle beam. The 4WD bracket mounts the pivot point behind the rear flange of the engine crossmember. The 2WD bracket mounts to the same holes but places the pivot point INSIDE the crossmember (See Axle Pivot Bracket 3K090 in diagram below). 

a) If you plan to install a suspension lift when doing this swap, then all you’ll have to do is use the brackets in your lift kit.

4) 4WD front axle assembly.

5) Front driveshaft.

Manual Transfer Case Conversion:

1) Remove the BW1359 dummy case.

2) Clean the gasket surface on the transmission tail housing, replace the gasket, and bolt on the new transfer case.

3) Remove the front seats and pull the carpet back to reveal the transmission hump. The hole for the extra shifter is already cut out of your truck. There is a metal trim piece under the carpet on the transmission hump that bolts to the floor to cover up unused portions of the hole (so a truck with an auto transmission and electric shift transfer case would have a solid plate, etc.). 

a) If you have a manual transmission, remove the shifter and floor plates. 

b) If you have an automatic transmission with a column shifter, remove the plate covering the factory hole in the transmission hump.

c) If you have an automatic transmission with a floor shifter, remove the shifter and floor plate.

4) Install the transfer case shifter and linkage. The linkage bolts to the two holes on the drivers side of the transmission tailhousing (see diagram below). Do not fully tighten them for now.

5) Trim the carpet JUST enough to clear the shifter. install the shift boots and trim.

6) Linkage adjustment: 

a) Put the transfer case into the low range position.

b) Then move the cam plate rearward until the bottom chamfered corner of the neutral lug just contacts the forward right edge of the shift lever. The lever linkage should be engaged in to the shift linkage on the transfer case.

c) Hold the cam plate in this position and torque the larger bolt first to 70–90 ft. lbs. and torque the smaller bolt to 31–42 ft. lbs.

d) Move the transfer case in cab shift lever to all shift positions to check for positive engagement. There should be a clearance between the shift lever and the cam plate in the 2H front and 4H rear (clearance not to exceed 3.3mm) and 4L shift position.

e) Install the vent hose. The cam plate has a notch for this that the hose slips in to.

7) Reinstall your manual transmission shifter (or automatic transmission floor shifter if so equipped).  

8) Plug in the harness that runs from the driver side inner fender (below the brake master cylinder) to the transfer case. There are (4) plugs. You want  the one closest to the engine. This connection isn’t necessary for the 4WD to work, it’s just to trigger the 4WD indicator on the dash.

9) Turn on the key, place the transmission in neutral, and check the transfer case 4HI and 4LO positions to ensure the proper 4WD dash light comes on.

Electronic Transfer Case Conversion:

The electronic transfer case conversion is much like the manual case conversion with a few exceptions:

1) Remove the rubber grommet in the floor under the drivers side seat.

2) Run the transfer case harness with the grommet (from your donor vehicle) through the hole on the floor in front of the drivers seat. 

3) Install the electric shift module behind the interior panel that’s behind the drivers seat and plug in the harness. The gray connector follows the transmission hump and goes up in to the dash.

4) Install the 4WD switches. In the 1989-1990 Bronco II, the 4WD switches mount where the left vent is above the radio. Other Bronco II models had the switches in a small console on the headliner.

5) Remove the dash and replace the main harness with the new dash harness.

6) Plug the harness in from the electric shift module and connect the 4WD switches.

7) Test the 4WD switches to see if the transfer case is working.

Below are diagrams of the electric shift control.

 

Electronic Shift Control

Wire Color

Purpose

Black Wire Ground
Black With Orange Stripe Wire From Electric Shift Control Module To Ground
Black With White Stripe Wire Hot At All Times To Electric Shift Control Module
Brown Wire Electric Shift Control Module To Transfer Case Assembly Shift Motor
Brown With White Stripe Wire Electric Shift Control Switch (4-Lo) To Electric Shift Control Module & Instrument Cluster. Also Electric Shift Control Switch To Transfer Case Magnetic Clutch Coil
Dark Blue Wire Electric Shift Control Switch (4-High) To Electric Shift Control Module
Gray Wire From Electric Shift Control Switch (4-High) To Electric Shift Control Module And Instrument Cluster
Light Green Wire Electric Shift Control Module To Transfer Case Speed Sensor
Light Blue Wire From Electric Shift Control Switch Gray Wire (From 4-High) To Instrument Cluster And Rear Anti Lock Brake Module
Orange Wire Electric Shift Control Module To Transfer Case Assembly Magnetic Clutch Coil
Orange With Light Blue Stripe Wire Electric Shift Control Switch (4-Lo) To Electric Shift Control Module
Orange With White Stripe Wire Electric Shift Control Module To Transfer Case Magnetic Clutch Coil
Pink Wire To Transmission Neutral Safety Switch
Purple With Yellow Stripe Electric Shift Control Module To Transfer Case Magnetic Clutch Coil
Red With Light Blue Stripe From Neutral Safety Switch To Starting System
Red With White Stripe Wire Neutral Safety Switch To Electric Shift Control Module
Red With Yellow Stripe Wire Hot In Start Or Run Position To White With Purple Stripe Wire To Electric Shift Control Module
White Wire Electric Shift Control Module To Transfer Case Magnetic Clutch Coil
Yellow With White Stripe Wire Electric Shift Control Module To Transfer Case Assembly Magnetic Clutch Coil
Yellow Wire Electric Shift Control Module To Transfer Case Assembly Shift Motor