I've posted some of this before without any resolution but have some more info since we got some snow here lately.

Edit: 1998 Expedition

The other night after some slushy snow I tried to get up my driveway and the rear just started spinning, so I clicked on the 4WD-HI and attempted to continue to no avail. I still could only notice the rear wheels spinning. I then put the truck in neutral and clicked on 4WD-Low, heard the "clunk" as it engaged, put the truck back in Drive and attempted to climb the driveway again to no avail. I had my wife check out the front wheels and they weren't spinning at all. I have LS in the rear and know you're supposed to give power gradually for it to work properly so I didn't gun it at all, just applied some power to attempt the climb. BTW, all 4 wheels were on snow with no dry patches.

Previously I've posted about a problem with the truck not wanting to stay in 4HI. When enabled, it will switch from 4HI to AWD, back and forth every so often but I swear the 4WD works as I've messed around in the snow to see the difference between 4WD and 2WD and notice a huge difference with 4WD. It's a '98 and the switch settings are: 2WD-AWD-4HI-4LO

About a year ago I did the actuator test by starting the truck and checking if the linkage moved at the transfer case when switching from 2WD to 4WD and it seemed to move fine. What other check could I do and for what purpose? I'm a little confused as to how the system should work. Should I get front wheel spinnage in 4WD? (I thought so) From what I know, the 2 solenoids on the firewall near the battery control 4HI and 4LO. If they were bad or there was a leak in one of the vac lines would the drivetrain indicator light on the dash still function correctly? When should I be able to spin the front driveshaft and how exactly do I check this? (Raise front-end only and spin wheels?) Does the front driveshaft always spin and the hubs lockup in 4WD?

Because my drivetrain will intermittently shift between 4HI and AWD I kinda assumed I had a vacuum line leak but I'm not positive. When it switches I can hear a relay clicking inside the truck. Does this relay control the solenoids?

Any help would be appreciated. Thanks!

 

I had the same problem over the last year. My 4x4 would work off and on. I finally found that there were about 10 different places on the original Ford plastic vacuum lines that were leaking between the solenoids on the firewall and the actuator on the differential. My lights on the dash were on showing the 4x4 was supposed to be working, but it wasn't. I tested the 4x4 by jacking up the rear wheels with a floor jack and putting it in 4x4 and the truck didn't move. I finally got smart and replaced the Ford plastic lines with 3/16 rubber vacuum hoses all the way from the firewall to the differential. PROBLEM SOLVED !!!!
No problem since and it has been over 6 months.

 

Cool, I'll try that first.

Was it a big job to do? I wouldn't expect it to be a big deal but I noticed the vacuum lines enter a wire loom near the solenoids and couldn't tell if they would be difficult to change.

Thanks for your help!

 

First things first... what kind of vehicle are we talking about here? Sounds like an Explorer? Could be a few different things, but it depends on what specific vehicle it is and what model-year.

-Joe

 

I have a 2000 F150 and I too just found out that my 4wd is not working. Same situation, I could not get up my driveway last snow storm. I checked underneath and when you engage 4wd the front driveshaft does rotate. The split axiles seem to rotate weather or not 4wd is on or off. I'm not sure if the front wheels lock to the split axiles or the split axiles lock to the drive shaft. I stomped on the emergency brake and tried to spin the front wheels in the snow but they would not move. Is there a better way to check to see if 4wd is engaging, if I jack up the front and try rotating tires by hand while in 4wd will I be able to see the front driveshaft spin? I have not been able to crawl under to check the actuator to see if I have a vacuum leak. I am trying to find a service manual on the location of the actuator and vacuum hoses, any help in pointing me in the right direction would be appreciated.

 

It's a '98 Expedition.

Last night I was at my parents house (in the boonies) and their driveway was full of mud/snow. As I tried to climb up a small incline I was slipping on snow/ice/mud and again only the rear spun when I set it in either 4HI/4LOW. It's supposed to warm up in a few days so I'll definitely get to working on it this weekend.

I haven't used the 4WD much at all (just on occasion to grease everything up) so I pray it's not the auto-hubs or anything in the transfer case.

As far as mileage I have 65,000 and have changed the tranny/transfer case fluid.

Thanks again!

 

Today I replaced both vacuum lines (pink and blue) from the solenoids to the vacuum motor and the front wheels are still not turning.

When I shift into 4HI I don't really hear anything but when I shift into 4LO I'm still getting that "clunk" like it's engaging.

The front axle was worked on for a small leak once and I'm wondering if they could've messed something up in there. Or, maybe they swapped the lines at the vacuum motor on accident? (What would that do?)

The vacuum motor seems to be working fine as it pushed the rod in/out (which switches a lever) about 1/2" when switching between 2WD and 4WD.

Anybody have any ideas?

 

OK, here's what you need to do:

Put the truck up on two sets of jack-stands. Start the truck, put it in 4 wheel drive, and look to see what's not turning. It's possible that the Center Axle Disconnect is still not functioning. It's also possible you have a busted CV joint internally, and the boot is slipping around the shaft (typically the boot clamp holds it tight enough that it will twist the shaft around and tear the boot.) It really sounds like something mechanical to me... if the front driveshaft turns, that eliminates the transfer case. If not, that's the root of the problem.

Let us know what you find.

-Joe

 

Ok, I jacked up the truck and the front drive shaft does spin in 4WD. The following is a what I've found so far:

- In park, truck running, 2WD selected, there is vacuum on the pink line all the way to the vacuum motor.
- In park, truck running, 4WD selected, there is vacuum on the blue line all the way to the vacuum motor.
- The vacuum motor seems to be working as I can see the plunger moving in/out of the motor which in turn moves a lever on the front universal. Previously I replied that it was about 1/2" which I think may be a tad more than what it actually is. I removed the vacuum motor and moved the lever on the universal and it does only move so much so I think the vaccum motor is working correctly.
- Truck jacked up and running, 4WD selected, in Drive, the front drive shaft from the transfer case to the universal spins when the rear wheels spin, but movement stops there. The front axles (whatever they are called - from the universal (pumpkin?) to each wheel) do NOT spin. So it seems the problem is at the universal.

I mentioned previously that I had the front universal/axle repaired by Ford under warranty as it developed a small leak. I rarely get to use 4WD so I'm not really sure if it's been working since.

 

I worked on my truck this weekend and this is what I found out. The blue vacuum line is used to lock the front split shafts or wheels to the front axial. The red vacuum line is used to disengage the front wheels. With the front of my truck jacked up I applied vacuum to the blue line at the connection just below the battery on the fender wall. I then spun the tire by hand and I could feel the wheel lock to the front axial. I then applied vacuum to the red vacuum line with the vacuum pump and then spun the tire and it spun freely. This proved to me that the vacuum actuator on the front axial was working. I then traced the vacuum lines up to (2) vacuum solenoids located behind the battery. One has a white vacuum line, (always active with vacuum) on the bottom and a blue one on top. This one is used to engage 4wd. The other has a black line, (always active with vacuum)on the bottom and a red vacuum line on top. This one is used to disengage 4wd. They both have an electrical connection on top to activate the solenoids. When I disconnect the electrical connection and checked the voltage I was reading 14vdc with the truck running. The problem is I cannot get the solenoid to activate to apply vacuum to the blue line to activate the actuator locking the front wheels. I also found out that the 14v was always on. I tried shifting my floor shifter in and out of 4wd but the 14v stayed constant. I tried looking under the vehicle for a micro switch that would turn the 14v on and off but the only sensor I could find was on the transfer case and it went to the dash 4x4 light. I would like to know if anyone knows what turns the voltage on or off to the vacuum solenoids. I removed the solenoids and I cannot get them to activate. I really think I have two problems. 1. The voltage to the solenoids stuck on and 2 it over heated the coils in the solenoids and they are stuck. Still trying!!

 

Here's what I found so far for Aycardus,

PINPOINT TEST A: FRONT AXLE WILL NOT ENGAGE


A2 CHECK THE FRONT AXLE


1 With vacuum applied to the outboard shift motor port, rotate one of the front axles and observe the other.

l Do the axles rotate?

è Yes

INSPECT the vacuum hoses for leaks, kinks, etc. REPAIR as necessary. If OK, REFER to «Section 308-07A». TEST the system for normal operation.

è No

REPAIR the front axle. REFER to «Section 205-03». TEST the system for normal operation.

Not very helpful, I'm sure... sorry. All roads lead back to removing and repairing the front axle, a tedious process to boot. I've got some diagrams of the axle assembly if it might help, but couldn;t find much more than that... sorry.


PG633, here's what I have for you so far:

PINPOINT TEST C: THE FRONT AXLE IS NOT ENGAGING CORRECTLY (TRANSFER CASE MOTOR MOVEMENT OK)
² C1: CHECK THE VOLTAGE OUTPUT FROM CJB FUSE 23 (10A)
² C2: CHECK CJB FUSE 23 (10A) AND BJB FUSE 104 (30A)
² C3: CHECK CIRCUIT 1052 (T/BK) FOR VOLTAGE
² C4: CHECK THE IGNITION STATES
² C5: RETRIEVE THE RECORDED GEM DTCS FROM BOTH CONTINUOUS AND ON-DEMAND SELF-TESTS
² C6: CHECK THE HIGH LAMP INDICATOR — TRIGGER THE GEM ACTIVE COMMAND HIGH LAMP ON
² C7: CHECK THE FRONT AXLE ENGAGEMENT
² C8: CHECK THE FRONT DRIVESHAFT ENGAGEMENT
² C9: CHECK THE FRONT DRIVESHAFT DISENGAGEMENT
² C10: CHECK THE FRONT AXLE AND THE FRONT DRIVESHAFT DISENGAGEMENT
² C11: CHECK 4X4 AND 4X2 CENTER AXLE DISCONNECT SOLENOID CIRCUITS — MONITOR THE GEM PIDS 4WDSOL AND 2WDSOL
² C12: CHECK 4X4 AND 4X2 CENTER AXLE DISCONNECT SOLENOIDS — MONITOR THE GEM PIDS 4WDSOL AND 2WDSOL
² C13: CHECK CIRCUITS 145 (GY/BK) AND 605 (R) FOR SHORT TO POWER
² C14: RECHECK THE 4X4 AND 4X2 CENTER AXLE DISCONNECT SOLENOIDS — MONITOR THE GEM PIDS 4WDSOL AND 2WDSOL
² C15: CHECK THE VOLTAGE TO THE 4X4 AND 2H CENTER AXLE DISCONNECT SOLENOIDS — CIRCUIT 294 (W/LB)
² C16: CHECK THE 4X4 CENTER AXLE DISCONNECT SOLENOID FOR CONTINUITY
² C17: CHECK THE 4X2 CENTER AXLE DISCONNECT SOLENOID FOR CONTINUITY
² C18: CHECK CIRCUIT 145 (GY/BK) FOR OPEN
² C19: CHECK CIRCUIT 605 (R) FOR OPEN
² C20: CHECK CIRCUIT 145 (GY/BK) FOR SHORT TO GROUND
² C21: CHECK CIRCUIT 605 (R) FOR SHORT TO GROUND
² C22: CHECK THE VACUUM AT THE 4X4 AND 4X2 CENTER AXLE DISCONNECT SOLENOIDS
² C23: CHECK THE 4X4 AND 4X2 CENTER AXLE DISCONNECT SOLENOIDS — CLOSED
² C24: CHECK THE 4X4 AND 4X2 CENTER AXLE DISCONNECT SOLENOIDS — OPEN
² C25: CHECK THE VACUUM FEED LINES TO THE VACUUM MOTOR
² C26: CHECK THE VACUUM MOTOR

Looks like aside from the basics you have already done, it's gonna mean (I hate saying this!) taking it into a dealer for an hour of troubleshooting. Sometimes instead of beating our heads against a wall trying to find out what the skinny is, it's just easier to pay someone who cahn tell you right off the bat what the problem is.

Sorry I couldn't be more help to you tow...

-Joe

 

Joe,

Thanks for the input. I have checked all the fuses. No problem with voltage. I tried looking in Chilton's manual but they do not cover 4x4 problems.

Berfore I take it in for service I would love to find out what controls the voltage to the vacuum solenoids. One would think it would be some sort of micro-switch on the 4wd shifter.

Thanks again for your reply. I will keep everyone posted on results.

 

PG633, I think I posted this some time ago, but here it is again... This is all it says in the 2000 service manual for the Manual transfer case:

The mechanical shift on the fly (MSOF) system is a manual shift 4WD system that allows the operator to chose between two different 4x4 modes as well as 2-wheel drive. The operator can switch between 2WD and 4H mode at speeds up to 88 km/h (55 mph). To engage or disengage 4L range, the vehicle speed must be less than 5 km/h (3 mph), the brake pedal depressed, and the transmission must be in NEUTRAL.

Shifts between 2H and 4H can be made at a stop or any forward speed up to 88 km/h (55 mph). At temperatures below 0ºC (32ºF) shifts should not be performed above 72 km/h (45 mph).

The transfer case is equipped with an electromagnetic cluch which is located inside the case. This clutch is used to spin up the front driveline when shifting from 2WD to 4x4 mode at speed. When the manual shift lever is moved, this activates the 4WD indicator switch, 4WD electric clutch relay, and the electromagnetic clutch. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle collar is engaged and the electromagnetic clutch is deactivated.


Now, for the electronic SOTF, there are some things that it would have in common with the Manual because the only physical difference between them is the actuator for the transfer case (the transfer case has the same part number regardless of whether it's manual or electronic. The difference is in the shifter: Motor or Lever).

Transfer Case — Electronic Shift on the Fly (ESOF) Operation

The electronic shift on the fly (ESOF) system is an electronic shift 4x4 system that allows the operator to choose between two different 4x4 modes as well as 2-wheel drive. The operator can switch between 2WD and 4H mode at speeds up to 88 km/h (55 mph). To engage or disengage 4L range, the vehicle speed must be less than 5 km/h (3 mph), the brake pedal depressed, and the transmission must be in NEUTRAL.

The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to spin up the front driveline when shifting from 2WD to 4H mode at speed. When the control switch on the instrument panel is turned, the generic electronic module (GEM) recognizes that a shift has been requested and activates the electromagnetic clutch and the relays which power the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the GEM, power to the shift relays and motors will be removed. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle collar is engaged and the electromagnetic clutch is deactivated.

Shifts between 2WD and 4H can be made at any speed up to 88 km/h (55 mph). Listed below are the inputs and outputs needed by the GEM to execute a change between any of these modes.

Feature Inputs:

l 4WD mode switch (various resistances; go to Table 1).

l Contact plate position inputs A, B, C, D (grounded when closed, open circuit when open; go to Table 4).

Feature Outputs:

l 4x4 shift motor relay outputs (go to Table 2).

l Transfer case clutch relay (grounded when relay is activated, open circuit when relay is deactivated).

l 4x2/4x4 vacuum solenoid (grounded when activated, open circuit when deactivated).

l Cluster indicators (ground when activated, open circuit when deactivated).

When shifting into or out of 4L, the GEM requires that the vehicle speed be less than 5 km/h (3 mph), the brake is applied, and the transmission is in NEUTRAL.

Feature Inputs:

l 4WD Mode Switch (various resistances; go to Table 1).

l Contact Plate Position Inputs A, B, C, D (grounded when closed, open circuit when open; go to Table 4).

l Output Speed Shaft (OSS) Sensor (Sinusoid Signal: 0.7V-20V, 2.2 Hz/mph).

l Brake Input (battery voltage when brake is depressed, open circuit when not activated).

l Transmission Range Sensor (grounded when transmission is in NEUTRAL, open circuit otherwise).

l Start/Clutch Depressed Input (go to Table 3).

Feature Outputs:

l 4x4 Shift Motor Relay Outputs (go to Table 2).

l 4x2/4x4 Vacuum Solenoid (grounded when activated, open circuit when deactivated).

l Cluster Indicators (grounded when activated, open circuit when deactivated).


If you notice, it says that in both cases, the GEM acts as a ground for the solenoids, so what you may try and do is manually run a pair of jumper wires to the vacuum actuator to check their function... put 14 volts in on the input side, and ground the other, and see if the axle lock shifts. If the solenoid works, check and see if the wiring is going to ground when you shift. You can use a continuity tester to see if the solenoid connector is grounding through the GEM. If not, it's possible that the GEM is bad, or there is a bad connection somewhere...

Also, double-check that the unlock solenoid is losing it's ground when you shift into 4wd... both of those things should happen at the same time: the unlock solenoid should lose its ground and the lock solenoid should become grounded. It's possible the unlock solenoid is stuck and it's trying to lock AND unlock at the same time. The solenoids for my truck are about $31, so hopefully that's the problem instead of the GEM!

Good luck! Let us know what you find!

-Joe

 

Thanks for the help, guys. I'm at a loss of what to do next aside from going to the dealer. I guess I was hoping that the vacuum motor just needs to be replaced but it seems to be moving that lever just fine.

If anyone has diagnosed this and could tell me about how far the lever should move I'd appreciate it. I'm thinking maybe the motor is on it's way out and perhaps isn't moving the lever completely to engage but I think I could be reaching for quick (and cheap) fixes.

 

Joe,

Thanks for the info. It is what I needed to know to finish trouble shooting the vacuum solenoids.

Both solenoids were working correctly electrically, but still no vacuum to output of solenoids. I removed both solenoids and sprayed WD-40 in both vacuum ports and blew them out with compressed air. To my surprise I was able to get both working. 4wd is alive.

I’m not sure if this is a permanent fix, but I will try to exercise 4wd once a month.

I appreciate all of the information supplied and if I can offer any more info to other please let me know.

Paul