This is provided for information purposes only and is not intended to be a service manual or guide of any type. The author does not accept responsibility for any problems caused directly or indirectly by this document.

Electronic 4WD Switch Motor “Re-Build”

1988 Ford Bronco II
4WD
2.9 L

Recently I purchased a Bronco II with shift on the fly 4WD. The vehicle would not switch into 4WD when I purchased it; because of this I was able to get a significant reduction in the asking price.

The root of the problem was the 4wd switcher motor. I had read on the ford-trucks.com forum that the motors simply got dirty and stopped working.

Tools Needed:
8mm Socket or wrench
10mm socket
6” extension
Ratchet
Wire Cutters
Wire Strippers
Gasket Scraper
Scribe
Tamper Proof T20 Torx Wrench

Materials needed:
Gasket material to form new gaskets, I used 1/16” cork.
12g weather proof butt connector
Electric Contact Cleaner
Degreaser that does not attack insulation or plastics
¼” long 3/16” fuel line

Work site prep:
1. Pick a 100 degree day
2. Make sure your work area has been exposed to the sun for at least 5 hours prior to starting the project
Optional your work area should be a gravel driveway
Optional liberally sprinkle cholla cactus thorns in your work area. These suckers are sharp and will painfully penetrate your skin with ease.

Switch Motor Assembly removal


Figure 1 Installed Switch Motor Assembly

Disconnect the negative battery lead on the battery.
Block the right side wheels to prevent the vehicle from rolling
Jack up and support the left side of the vehicle using jack stands
Locate the 4wd switcher on the transfer case. It is on the left side of the vehicle about ½ way back.
Carefully disconnect the wiring harness to the motor. Be careful; do not break off the connector locking tabs like I did.
Remove the wiring harness connector bracket from the vehicle. (2 - 10mm bolts)
Cut the BROWN wire that runs from the connector to the transfer case at the midway point.
While supporting the motor remove the 4 – 10 mm bolts (3 on switch housing, 1 on bracket on back of motor) that fasten the motor assembly to the transfer case.
While supporting the motor, carefully remove the magnetic sensor from the transfer case.
The motor assembly can now be removed from the transfer case.
Take note of the position “Drive” selector.

http://worleybird.com/bronco/selector.jpg
Figure 2 "Drive" selector

http://worleybird.com/bronco/back.jpg
http://worleybird.com/bronco/front.jpg
Figure 3 Motor Assembly On the bench

Motor Disassembly

Clean the grease and dirt from the outside of the motor assembly using a degreaser that does not attack wire insulation or plastic.
Scribe a mark showing the position of the selector

http://worleybird.com/bronco/posit.jpg
Figure 4 Mark showing position of selector

Remove the bracket from the back of the motor (2 – 8mm nuts)
Remove the 2 – 8mm motor bolts from the back of the motor, these are long bolts.
Remove the back plate of the motor
Remove the motor “can”. The magnets in the can are quite strong and will cause the armature to be removed with the can. Be careful not to loose the brush springs when the armature is removed.

http://worleybird.com/bronco/motor.jpg
Figure 5 Disassembled Motor

Switch Disassembly

Scribe an alignment mark between the Switch Cover and Switch Body. This is a very important item as the selector logic depends on the alignment.
Remove the 3 – Tamper Proof T20 screws that secure the Switch Cover
Carefully Remove the Switch Cover
Remove the Selector Gear
Remove the Selector Gear Bushing

http://worleybird.com/bronco/switch.jpg
Figure 6 Disassembled Switch - The "Chunks" in the lower left are from a disintegrated rubber bumper mounted on the selector gear

Motor Cleaning

Degrease the armature
Clean the contacts on the armature – I used a well used brown scotchbrite pad

http://worleybird.com/bronco/armature.jpg
Figure 7 Cleaned armature

Clean the brush holders
Clean the Switch Housing – make sure to remove the old grease
Clean the motor can
Clean the back plate

Switch Cleaning

Finish cleaning the switch housing
Clean the switch fingers using contact cleaner
Carefully degrease the selector gear – Take care not to damage the selector circuit board riveted to the gear
Clean the selector circuit board riveted to the gear using contact cleaner
Clean the selector gear bushing

Motor Assembly

Grease the drive end of the armature shaft. I fully packed the worm gear.
Lightly grease the armature shaft between the worm gear and contacts.
Re-install the brush springs and brushes
Install the armature into the switch housing while holding the brushes and brush springs in place. It’s not that hard to do, and took me about 30 seconds to install the armature.
Re-install the motor can. I temporarily installed the selector gear with the stop positioned to prevent the armature from being pulled out of the housing.
Lightly grease the short shaft on the armature.
Re-install the back plate
Re-install the 2 motor bolts

At this point I bench tested the motor to make sure it ran in both directions (Solid Orange and Solid Yellow Wires)

Switch assembly

If needed replace the rubber bumper on the selector gear using a small piece of 3/16” fuel line. I trimmed the sides of the tubing to get a bit better alignment.

http://worleybird.com/bronco/gear.jpg
Figure 8 Selector Gear with fuel line bumper

Install the selector gear bushing
Lightly grease the teeth on the selector gear
Install the selector gear making sure that it is aligned with the mark you scribed earlier
Install the switch cover making sure that is aligned with the mark you scribed earlier using the 3 – Tamper Proof T20 screws

At this point made the electrical connection to the Selector assembly and hooked up the neg battery cable. I then checked to make sure the selector worked with the key in the run position. I had success.

Re-install the Selector Assembly in the vehicle using a reverse order from removal.
Repair the brown wire using a weather proof butt connector, or some other water proof means.

I did fabricate replacement gaskets, where needed and also used RTV.

PDF VERSION - http://worleybird.com/bronco/rebuild.pdf

 

THANKS FOR SHARING!!!! Info like this is why I keep coming back to this site. THANKS!!

 

Good job keep passing the info!

 

I have a 1987 XLT Manual with the same problem not going into 4wd anymore, and don't know where to start looking to fix this problem. I notice motors on the transfer case but wonder if it could be something minor to start with first. I have had it since 1987 and never a problem with 189K miles.

 

Hey Staplegun,

You did a great job documenting a fix for that electronic 4wd hub shifter. The only thing i would add on the rquirements is that the weather should be above 70% humidity and 75% chance for rain! Otherwise we all love the challenge of finding that screw or nut that popped off and landed in the gravel someplace and we really don't know what it looked like! lol Although I have manual hubs on my 86 4wd EB, i will think there will be lots of people in need of this info. The links to pics don't work correctly but that's a Ford-Trucs.com issue. ANyone can copy each link and paste it in a new window and they will work. I downloaded the pdf and it works fine, i will share it with credit to you!