92 EB 4x4 broke - no clicks from rear

[DrkPony]

4x4 button does nothing, I do not hear any clicking from the rear of the car. Any suggestions? Thanks

 

[Burns]

check the fuses and relays.

 

[Bwana Bob]

Mine failed too!

Mine is doing the same thing. I was all set for the big snow, punched the 4X4 button and... nothing.:roll:

Maybe we can troubleshoot this together. Here is what I did so far. It was too cold yesterday to do anything more:

I unplugged and checked the connectors at the transfer case and sprayed them with contact cleaner. This worked in the past, but this time, no go.:thumbdwn:

20 amp fuse for the transfer case in in the power distribution box, under the hood, passenger side fender: Checks OK.

I get one click from a relay in the 4X4 control module ("computer") in the driver's side rear (behind the jack access panel), but no lights, and no action from the shift motor.

At the control module, I pulled the large connector on the left and checked for proper continuity from the sensing switches on the shift motor. I verified that the sensors are saying its in 2WD mode, so the control module should know where it is.

Pushing the white test button on the control module produced a steady red light. I'm not sure what this means.

I have the Ford and the Haynes wiring diagrams, which are a big help. There are some excellent threads here on the shift motor. Check out the Singleton info in the Explorer Maintenance Tips section. Also, see the excellent sticky in the Drivetrain forum.

From what I've read, 99% of the problems can be fixed by overhauling the shift motor, but I'm not sure this is my problem. There are two possibilites in my case:

1) Shift motor isn't working, or
2) Shift motor isn't getting voltage from the control module.

I'm good with electronics, but I haven't seen any info on troubleshooting or repairing the control module. I know it senses the transfer case position, has some logic and relays in it, and presumably a power transistor or a big voltage regulator, judging by the heat sink on it. Anybody familiar with the guts of this unit? Also, what is the function of the clutch solenoid in the shift motor assembly? Does it operate independently from the motor?

Thanks.

Bob

 

[Bwana Bob]

Update: Weekend troubleshooting. I didn't have much time and it was too cold to do much, but I did a little troubleshooting.

Position sensor appears to be sending the right info.

Control module is sending voltage to the motor, but voltage is dropping to 8.5 V (vs. 12 V, engine off). May be a poor connection between the power ditribution box and the control module. I don't think so, but I'll do a load test anyway.

It really looks like the shift motor is not running but is drawing excessive current. Possible causes: Shift motor commutator is shorted with carbon tracks, or shift motor is jammed hard against the stop.

Its not likely that the transfer case itself is jammed (I hope) because it hasn't been abused in any way.

So, this weekend when it gets a little warmer, I will pull the shift motor assembly. Fortunately, there are excellent shift motor overhaul threads on this site, better than any shop manual.

Does anyone know the function of the magnetic clutch (brown wire) that is inside the transfer case? Can I turn the shifter to 4H without energizing this clutch?

Bob

 

[TedJ]

You won't have any problem shifting the 'case manually. Just grab that shaft with something that won't mess it up and turn it to whatever mode you want. I've heard of many people doing this without one mention of the brown wire. You can rule out the mechanical part of the 4x4 system if it works when you shift it manually.

edited, did some research because I wanted to know what the brown wire & clutch really did

From the ford service manual:

Electronic Shift Operation

The transfer case is equipped with a magnetic clutch, similar to an air conditioning compressor clutch, which is located inside the transfer case adjacent to the lockup sleeve. The clutch is used to spin up the front drive system from zero to vehicle speed in milliseconds. This spin-up allows the shift between 2-high and 4-high to be made at vehicle speeds listed in the vehicle owner's guide. The spin-up engages the front lock hubs. When the transfer case rear and front output shaft reach synchronous speed, the spring-loaded synchronizer sleeve (7106) mechanically engages the mainshaft lockup hub to the chain-drive sprocket and the magnetic clutch is then deactivated. Shifts between 4-high and 4-low can only occur with the transmission safety switches closed. The vehicle's speed must also be within specified limits as determined by the transfer case speed sensor (3 mph or under).

In english:

The brown wire powers a clutch that allows the front drivetrain to be spun up before it is engaged so that you can shift into 4H on the fly. If it did not have this clutch, you would have to come to a stop before shifting, or you would grind the gears in the 'case.

Since you're not going to be shifting on the fly (unless you can drive and crank the selector on the case at the same time. I'd pay to see that lol.....) the drivetrain won't be moving so the clutch isn't needed to synchronize the front and rear while shifiting

REALLY SIMPLE: Unless you can manually crank the selector while the vehicle is moving, you don't have to worry about the brown wire & clutch.

-Ted

 

[Bwana Bob]

Thanks, Ted. I wondered when that clutch comes into play. I have manual hubs, so if they're locked and I'm moving, the front drive is turning, but I presume that you need the clutch anyway to get front and rear synchronized.

This weekend I will pull the shift motor off and overhaul it and let you guys know what I find.

BTW, new and rebuilt shift motor assemblies are available from NAPA. New ones are $120; rebuilts are $82 minus a $30 core credit. Not a bad price.

Bob

 

[TedJ]

Yep, you still need the clutch/brown wire with manual hubs. Rebuild it and you should be good to go. Hope it works out for you.

-Ted

 

[redneck2725]

I think i have the same problem. I will be looking to re-building the same part

 

[Marv]

I had the same problem with my 94 Explorer,
Shift motor quit working, the problem was in the sensor circuit on the shift motor.
Sensor unit was sealed and had to cut plastic ring on the inside to open it up. The wheel had fell off the shaft that rotates it, figured out the alignment and glued it back on with super glue. Works fine now.
That small rubber bumper on the gear that had been mentioned in serveral write ups in other post is not needed, if the gear travels far enough for the gear to hit the stop, then the sensor wheel was out of alignment to let it travel that far.

 

[Bwana Bob]

Share my joy!

Well,she's fixed! I overhauled the shift motor assembly on Sunday. The plastic bushing was shattered into little pieces. Some of it was even embedded in the teeth of the drive gear.

In my case, the controller was sending voltage to the motor, but the motor wasn't turning. It must have been either jammed against the stop or the overtravel caused by lack of the plastic bushing confused the controller into trying to run the motor in the wrong direction, hard against the stop.

I noticed on the gear housing that there are some index marks cast into the housing and the sensor cover. Presumably these are used to align the switch contacts. It looked sort of like an interpolation scale.

I got it all tested and buttoned up just as the first few snowfklakes appeared.

Thanks to all who shared experience, especially to Brain for his excellent overhaul procedure, better than any shop manual.

Price of Torx bit: $5.00. Price of rubber fuel line: $0.00. Sound of tranfer case engaging (click, click, clunk) and sight of "4X4" light on the dashboad: priceless!

Bob