Bruski13

99 xlt sport, shift on the fly 4wd. Worked off and on for a while. The light would come on in the cluster but wouldn't shift into 4hi or 4low. Would let sit for 30min or so and would work. Then it eventually stopped. Any suggestions?? My vacuum lines have vac from the solenoids and to the actuator but nothing. Im thinking either actuator its self is bad or maybe the shift motor on the tcase. I've heard the front shaft shouldn't spin when the 4wd isn't engaged but, mine does. Im sure there is already a thread on this but I searched and couldnt find it. Need 4wd with retarded ky weather and a long, steep dirt drive.

Cdn Paratrooper

Mine is acting up as well...these years of F150 have the worst 4X4 system going I believe..it is far too complicated a system and is always failing...there are days that I could just get rid of the truck in a minute because of the crappy 4X4 system..

Tomorrow it goes in again to see why it isn't working, it is really embarrasing to have a 4X4 that isn't...

If this doesn't fix the problem, perhaps I will look at what truck has a better system and buy it based solely on that fact.

Bruski13

What are the symptoms of yours?? Im not for sure what's wrong with mine so im trying to find out as much as I can. Its getting annoying and like you said, embarrassing having a 4wd that doesn't work. That's what I bought it for...

2003XLT

First things first check and see if your front drive shaft is spinning when in engaged if it is next step

Check all vacuum lines make sure nothing is cracked broken or missing if that's good

next step is to watch the 4x4 linkage on the left of the front diff cover the oil filter drain or big black cover held on by three 10mm bolts comes off and there is your linkage if that moves in when engaged and out when disengaged next step ( lube that pin that moves it loves to seize up)

Two the left of the diff on the drive axle there is your shift fork it's 4 bolts I forget the size and you can either separate the axle from the diff or take it out I recommend you just separate it there a few 12mm 12 pt that hold it together (MARK IT WITH A SCRIBE OR CHISEL)

Check the shift fork there are two plastic tabs on the ends and if they are sheared off then it won't engage one of those few things is all I've seen go wrong with these trucks with there phenomenal SOF 4x4

I personally hate it I would rather lock t hubs and manually pop it in 4x4 but hey that's just me...

I'm sure I missed something I'm at work let me know how it goes if you need any help let me know

I posted a few pics of everything and the last one is a picture of what the shift fork looks like new those are an upgraded brass tab I believe someone in this forum did but stock tabs are square white plastic ones they sit on a thrust bearing

Cdn Paratrooper

"Bruski13-What are the symptoms of yours?? Im not for sure what's wrong with mine so im trying to find out as much as I can. Its getting annoying and like you said, embarrassing having a 4wd that doesn't work. That's what I bought it for..."

The main symptoms are the lights are on and no 4X4 is home...when I switch it to 4H, the lights come on, all the clicking goes on in the dash but there is no 4H...I found out it is the differential vacuum actuator-the diaphram is done....

Very annoying system but I also found out Ford isn't the only one using this system....I mean what company in their right mind would use plastic bits in a system like this?

I am with tugs90, I like manual systems-they rarely if ever leave you stranded like this system has the potential to do....

Bruski13

My front shaft spins but my 4wd isn't engaged, well the turn dial and dash light say its not. When I turn the dial nothing happens, no movement by the actuator, not clicks from solenoids, nothing. Im thinking my shift motor on my tcase is out and my front shaft and front diff are still engaged but my hubs aren't, thus not giving power to front wheels. I tried tapping the shift motor and nothing happened. I sprayed the s*** out of the actuator with PB blaster and let it soak in nice and good and nothing. Worked fine when I got it then gradually started acting up. Turn the dial, nothing would happen. let it sit for a while then would work, or unplug the solenoids in the engine bay and plug back in and it would occasionally work. The solenoids in the bay have vacuum but the actuator does not. Don't know if vacuum is applied only when the shift motor says to engage 4wd.

Triton-SAS

When you engage it at the switch the solenoid it activated and sends vaccum to the front diff to lock it in. Are you sure the solenoids are good? Check the lines and connectors that run to the diff for leaks. Glad I don't run that setup anymore. Love manual hubs. Never swapped the t case actuator but have had mine completely apart before and reinstalled so if you need help I might be able to help you out with that.

Bruski13

When I take the lines off the solenoids there is vacuum on one of the two lines coming from both the engage and disengage solenoids. Could I use a compressor and shoot a little bit of air in the actuator and check to see if the diaphragm is bad?

Triton-SAS

That I wouldn't really know I removed the system completely from my truck before I ever experinced a problem with it.

2003XLT

If the linkage is moving then the diaphragm is moving if it's engaging an the front shaft is spinning and you have vacuum then I would say your right Replace it and see what happens I would pull that motor out of a scrap yard just to see if it is the weak link before you go ahead and spend big money on it I have never replace mine but everything else with this 4x4 I'm selling this thing it's just or headache after another and the funny thing is when I was wheelin it and givin it a good beating nothing broke just after I started driving it normal I had a shock blow out... Just one like wtf who has ever had that happen I've replaced both front hubs passenger side twice all shocks rear end front end re geared it at that time upper control arms lower ball joints I've under coated 3 times and bought some wheels and tires and a tonneau cover a programmer an auto start bull bar fog lights 3 sets strobe lights just endless money pit haha now it's gettin mileage on I think I'm gonna get a 250 maybe a 350