ok 2003 Lariat SC. 165,000KM. I have been stuck twice with the front diff not locking in? With the truck in the air (yes on jack stands), The truck will not shift into or out of 4WD on the fly (OTF). I am under the impression that there are two solenoids on the firewall? Where are they and how do I check them?

 

Front wheels off the ground, the key on and the truck in park does the front drive shaft turn? It should not.

JMC

 

The 2 silonoids are right behind the battery. If you go under the front diff. and remove the plastic cover you will see the the actuator. There are 2 hoses on it. One has vacumm on it in 2 wheel and the other in 4 wheel.
If you don't then one of the vacumm silonoids is bad or the hose from the silonoid to the auctuator has a hole in it.
bullseye670..................

 

You're not too clear on what you mean by, "shift into or out of 4wd on the fly".... Is it not engaging the transfer case? Are the light(s) on teh dsah coming on or not? We need more info... manual or electronic t-case? When it fails, are the lights coming on or not? The quick check JMC mentioned will narrow it down to being either a t-case issue or a front axle issue. Nobody can jump to any sort of a diagnosis with the information given.

-Joe

 

OK .. Yes the transfer case is engaging. the light on the dash is showing the truck is in 4X4. Electric transfer case (Supercrews didnt come with a manual). At this point, when the truck is in the air and I enguage the 4x4 all four wheels turn, disengaging the dash switch and only the rear spin. I have left it in 4x4 with thte wheels turning, put it back on the ground and taken it out on the road. The 4wd seems to fail when there is resistance (vehicle wieght and road surface). I would assume it may be the transfer case electomagnetic clutch?

 

For the record, some supercrews did come with a manual t-case. I've driven one personally. It depended on the trim level. ESOF was optional on teh XLTs, MSOF was standard on the XL and XLT, ESOF standard on the Lariat and King Ranch (IIRC).

The electromagnetic clutch on your truck is only used to synchronize the driveshaft speeds when shifting on the fly. Once the lockup collar engages, the electromagnetic clutch disengages, as you have a mechanical link at that point.

A few possibilities come to mind, but none of them will be easy to troubleshoot. It's possible that the transfer case chain is slipping, and that could be due to a worn or damaged chain, gears, etc. inside the case. It's also possible and, IMHO, more likely, that the center-axle disconnect is damaged or not fully engaging and being forced to separate under load. It's also possible that you still have a sticking solenoid and the system isn't fully engaging the front axle. You need to troubleshoot the vacuum solenoids that engage and disengage the front axle.

-Joe

 

I have checked the vacumme operated switch which moves the lever on the front Diff. when the truck is in the air and the 4x4 is engaged the vac switch moves the lever side to side to engage disengage the (shift fork in the front diff I assume - I dont have a break down or schematic) lever.

 

I have heard on one instance of the shifter fork being bent and causing issues? Again, I dont have a schematic so I am at a loss on this one?

 

the shifting fork can flat be broken off too. I've had to replace a shifter fork in a 2001 f-150. not too hard of a job, take all the drive shafts loose from the front diff, then take all the mounting bolts out, drop the diff out the bottom and from there it's a piece of cake, split it apart on the passenger side of the pumpkin, and the shifter fork is right there, flush out the old fluid and refill w/ new and away you go. about like 130 for the kit to do the shifter fork. probably around 200 for labor at the dealer.

 

Ok .. Just got the truck into the dealer and the issue is as such:

The front diff shift fork has lost a plastic (Delrin) nub off of one of the fork fingers. This causes the 4x4 to engage and disengage on its own (although the dash lite says 4x4). More specifically, when you turn the front wheels to the right, it causes the shift fork to bind and disengage the locking collar in the diff. So, as your cruizin down the highway, assuming your in 4WD, and go to pass another vehicle you have issues when you go to return to your lane and the rear of the truck breaks loose. Heads up guys!!

BTW.... parts on order.... minimun of 10 days to get them!!!