Replaced my front actuator last year with a Dorman 600-300. It was a 1/16" off of the Motorcraft it replaced, and I shaved it a bit if I recall, but seemed to work fine (fully disengaged on start up and fully engaged 4x4 as required).

Noticed vibratation start a week ago at above 65 mph (105 km/h), seemed quite similar to previous experience of actuator fail. Solenoids on firewall and vacuums (-16") at actuator checked out fine, but notice there is no disengagement movement at all on start up. It still engages 4wd fine.

Before I replace again, does anyone have insight on what might make the actuator fail so soon?

 

Because it's a Dorman...............

 

x2 on the Dorman.

I found that most of Dorman's parts are cheap, just to get you to replace it then be able to sell your vehicle as "working" to the next poor chap.

 

That Dorman part says it has a "lifetime" warranty so maybe you can get it replaced for free?

Dorman is one of the few companies making that part, the Ford replacement part is $335 vs $100 for the Dorman.

 

You can try.

Here's Dorman's LLW: http://ecx.images-amazon.com/images/I/81KyTMCOkwS.pdf

There is a reason the MC part costs more -- OEM compatibility. No 1/16" shaving req'd....

 

Tough to put up $300 for that part, maybe I'll try a junkyard first

 

Try the warranty first.

 

As I understand you to say...…..there is no disengage at startup.
There is not supposed to be if the Actuator is already in the released position,.
Next, 4wd engages fine..
The Actuator vacuum diaphragm is the same for both in and out and likely has no fault.
Are you sure the fire wall solenoids are not sticky or frozen.
They have a small cap on top that allows air to enter for release.
The filters get hard and crumbles ending up around the internal pistons causing an operational problem.
Be sure before you replace the Actuator on a hope..

 

Vaccuums both -16", 4x4 engages fine, seems to disengage fine. Started new thread on vibration.

 

I have a similar problem here My truck seems to be stuck in 4wd but the 4X4 light on the dash is not on but I can feel it when turning because of the dragging feeling, and when I took the 4X4 actuator off the transfer case it said it was in 2H and when I manually put it in 4L it jerks a little like it engages and when I put it back in 2wd it is still stuck in 4wd

 

It sounds like the Vacuum Actuator in the front has not released. Might be the Vacuum line fault between the firewall solenoids and the Actuator..
If the Transfer case motor is in the 2wH position, the dash light will not be on, as you observe and no transmission drive to the front but the wheels will still be locked together.
You need to take the cover off and look at the position of the Arm to verify this.
If it is off normal, manually move it back to disengage the front lockup. What the ARM does is move an internal Splined Collar to hook two axles parts together on the passenger side.
Then find out why.
It may be as simple as the Actuator needs to be replaced, or the internal Yoke that moves the Spline has broken or worn.
Verify before just changing parts.
.
Note: If 4L works, the case motor works and the Transfer case goes into low range Ok. Leave then alone if that is the case.
Good luck.

 

I believe for 97-03, the vacuum actuator requires vacuum in 2wd and 4wd, Easy check with gauge, should be ~15" vacuum. The solenoid can be checked with multimeter, resistance across both sets, and or vac checks at solenoid when switched.
Easy check, grab your cell and put it under the actuator and record (or have buddy watch), should pull slightly one way on startup (assuming in 2wd), then move the other way when 4H is engaged.