Front Diff Disco Actuator...Baffled! | Ford Explorer Forums - Serious Explorations

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Front Diff Disco Actuator...Baffled!


New Member
August 8, 2017
Reaction score
City, State
Burnaby, BC
Year, Model & Trim Level
1996, Explorer, XL
First of all, this is my first post here...seriously, the knowledge you guys have has gotten me through most of my repair question.
My apologies in advance...This is gonna be a long, but an issue I've been having since January has taken me on a wild ride, and today just got stranger. I've searched tons, and never found a resolution, but maybe this post may trigger an a-ha moment for someone else.

I have a 96 Explorer that has been absolutely an awesome vehicle for my the heck out of it, do most maintenance myself, but anything I can't do in my lot, I get it routinely inspected for.
We had a pretty rough winter this year, and one night after needing to use 4 low, (which i rarely do) I started getting a rhythmic thump in the driveline while in 2wd. About once per second regardless of rpm and vehicle speed up to around 50mph, especially after a left turn. Thought for sure the spider gears might be acting up in the cold.
More scary, was at highway speeds, I wouldn't get the thump, but it felt like my wheels were locking up, like quick little spikes on the breaks....enough to see my speedo and tach twitch with each "spike".

If I cranked the wheel a little to the right, it would dissipate. I knew I was going to be rebuilding the rear diff as it previously had signs of spider gear damage after a careless mishap by an inspector at our local smog check facility.
I repaired it, and the rear was smooth, but that thumping noise continued off and on.
Worst possibility was a transfer case. Transmission was rebuilt earlier in the year. Been perfect.

One morning the thump was real bad. On a lark, I switched it from 2wd, to 4auto. Noise was gone instantly.:dunno:
Hmmm..then while coasting, put back into 2wd, noise resumed. Quickly shifted into neutral to rule out tranny...noise persisted.

Ok...searched all over here and every other Ford forum, and some threads were about the same issue. Rhythmic thump, same timing, and speed range but most ending in a wasted case. A mechanic i went to confirmed my suspicions that the 4405 was prone to failure issues in their case design, and he had to repair a number of them this Spring, and many that were made for my truck are long gone from our local wreckers.
I searched high and low....not one available for well over 3 months.
I've been luck...driving in 4auto, all has been well, but real nagging doubt about how long the case would hold was getting louder, didn't want it to grenade on the hwy. Which I take to work daily.

My local Trans shop was helpful, and found some rebuilds Stateside, but asked me to bring my Ex in for a check of anything else that may be needed when ordering the TC.

Now it gets weird.
I dropped off the truck this morning, and 2 hours later, I got a call from them asking if I had removed the vacuum lines, and sensor harness from the front disco actuator.
I said I hadn't of course.
He said everything from the solenoids to the vacuum reservoir, and down to the disco diaphragm had been removed, and the thumping was not the t case but the slip collar in the front diff was partially engaging, and bouncing in and out of 2wd/4wd lock.:frown:
So.good news...Don't need a new case, bad news...what the hell has this done to my front diff?
At any rate, he pulled vacuum to actuate 2wd, but said it could drift back without constant vacuum, but he didn't have anything on hand to get it done today.
The truck drives a lot better. Felt a couple little thumps, but 95% better.

Now, over to you guys.
Can any of you think of any reason at all these lines would have been removed?...maybe an interfernce issue during a repair? I had some ball joints done around January, and while it was apart, had them throw in my Rancho shocks, but can't see those lines getting in the way.
Is there a possibility they just degraded and slipped off the diaphragm? Maybe dangling, they got pulled off the solenoid harness?

Can any of you think this may have been done intentionally to hide some other issue? If 4wd was throwing codes for the previous owner, maybe he or his mechanic pulled the whole deal, and none of us ever noticed them missing. 4wd worked during this whole tranny guy said that 4wd was definitely engaged somewhat...all the driveability issues were in 2wd only.
Again...apologies for the long post, but I have been through a lot of stress over this....think I'll go to a dealer to go over the missing parts, but is there any known issues with 2nd gen front diffs that pulling the vacuum lines and sensor cable would somehow half a$$ed fix or hide?

Thanks all!