4WD auto,hi,lo - binding in auto

[entoptics]

I just replaced my transfer case shift motor on my 2000 XLT (Thanks to this forum). This truck has the AUTO, 4HI, and 4LO dial on the dash. The new motor fixed my problem of no 4LO, but now the truck is often binding up and making whining noises when I turn corners in AUTO mode on dry pavement.

At first I thought it was not returning to the AUTO position from 4HI or 4LO, but upon testing, there is a VERY CLEAR difference in the amount of binding/noise when turning. 4HI immediately binds around sharp corners every time. When the truck is in AUTO, it is more intermittent, and less pronounced, but still very noticeable. I should add that prior to the replacement of the shift motor, the binding only happened VERY rarely, and the whining noise NEVER happened.

Any suggestions for what the problem could be? It seems to me that the transfer case is being WAY over zealous about applying power to the front wheels when it's in AUTO mode.

 

[gijoecam]

It's not the transfer case, it's the control system. The GEM monitors the wheel sensor inputs from the axle speed sensor and the front ABS sensors (Or the front output shaft speed sensor... dpeends on the year). When it detects a significant difference in axle speeds, it ramps up the duty cycle on the transfer case clutch until it sees the wheels turning the same speed again.

As for what's causing yours, it's a tough call. It could be a sensor on its way out, or it could be a bad wire or connection causing the signal to drop out when cornering. Without hooking up a monitor and taking it for a drive, it's tough to know what the system is seeing and, therefore, why it's engaging the transfer case when it shouldn't.

-Joe

 

[entoptics]

I got underneath and disconnected the brown wire from the wiring harness at the shift motor. This caused the truck to lose 4WD completely. No binding or hopping in AUTO, 4HI, or 4LO (definitely went into low range, just no power to the front wheels).

I was under the impression that the brown wire only affected the AUTO setting, but apparently not.

Any suggestions on troubleshooting from here?

 

[gijoecam]

The brown wire is what feeds power to the transfer case clutch coil. Without it, the t-case cannot lock.

Without seeing the GEM Inputs and outputs (PIDs) it's impossible to guess what's causing it. The most common cause, in my experience on these boards, is a failing rear axle speed sensor (on teh differential) but there's no guarantees there. For $10, some opt to give it a shot, and often times it works.

Personally, I'd find a shop with an NGS or WDS tester and have them monitor the GEM PIDs while it's happening. That'll usually make it apparent what's causing the system to think it needs to engage.

Sorry I can't really be any more help...

-Joe

 

[IZwack]

Bwm?

 

[entoptics]

I've considered the brown wire mod, but for now I would like to get everything working properly in stock form. Also, the Mrs feels "more secure" with the AUTO mode (don't ask me why).

After a bit more research (saw some pictures and descriptions), I suspect maybe the speed sensor is bad. The reason I suspect this, is that I likely tore it up myself when trying to remove the shift motor the first time. I thought it was a wiring harness connector, and buggered it up trying to pull it out. I broke off the bolt tab, twisted the sensor a bit, and tugged vigorously on the wires.

I damaged the one on the passenger side of the T-case. Is that the rear speed sensor? And are the part numbers different for the two different sensors?

I'm thinking I'll replace that before I take it in to have it professionally diagnosed.

 

[entoptics]

I replaced the sensor ($55 from Ford stealership) and that seemed to cure my problem. I'm not positive yet, as I haven't been anywhere were the AUTO 4x4 engaged, but it's certainly NOT engaging all the time now. No more binding and popping on corners.

4x4 works in HI and LO now, and it seems to stay in 2HI when left in AUTO position on dry pavement.

Thanks for the suggestions. I spent a total of $160 and 4 hours of labor, so you folks helped me save $350-$450.:notworthy