First off, let me state that my truck has been offroaded a bit in the past, so the 4x4 has gotten a workout.

Last year I ended up having to use 4WD HI for the first time in a while. Everything worked fine until I went to disengage it. About 200' after switching back to 2WD, there was a big clunk along with a bump in the front end, then everything was normal.
Now every time that I switch to 4WD HI it goes right in, however when I try to go back to 2WD it clunks and bumps when disengaging. It doesn't matter if I'm stopped or moving when I turn the switch over, I go 200' and it happens.

Does anybody have an idea of what I can be dealing with? After searching, it looks like it could be the 4x4 module or maybe low transmission fluid in the transfer case... that seem right? More importantly, is it ok to drive like this? We're in for a bit of snow here and I'll probably be using the 4WD a bit this weekend. I don't want to crash, but I can't afford any unnecessary expenses either if I can let this slide.

 

Well, a serious mechanical malfunction aside, the solenoid driven clutch that allows "shift on the fly" to 4HI could be sticking. I don't know that the 200' thing has much to do with it -- probably it just eventually jars loose.

The relay in your controller could even be sticking on I suppose.

The controller for the system activates the brown wire that goes into your transfer case. If you look closely you'll see that wire all by itself goes through a grommet into the body of the case.

When that brown wire is powered up, a solenoid engages the front driveshaft. The idea is to get the driveshaft up to speed using the clutch before the full hard engagement happens. That way the front part of the drivetrain is spinning when full power gets applied.

It's possible that the solenoid is sticking somehow keeping that clutch engaged and then suddenly releasing.

The other problem is more sinister and would involve the shift fork not releasing when the motor tries to retract it. Not sure enough about the mechanicals inside to comment on that.

Hows the lube look in it? Have you checked the level?

Also, after driving in 2WD for awhile get under there and carefully feel the tcase temperature. If it's getting very hot it could be that the lube pump isn't working right and that's inducing the other problems.

On all of this, I'm just guessing.

 

I'll check the heat of the transfercase next time I get the chance to crawl under. As far as the fluid levels, I changed out the fluid in the transfercase some time last year, which makes me worry, because I've never done it before. The front seals have been leaking for quite a while, so it is possible that there is not enough fluid in the front diff.

 

Sorry for bumping a thread that is almost 2 years old. But I am trying to search an issue I started having with my truck last week, and it has the identical symptoms to what the OP stated.

I have a 2003 FX4, a short time after I shift out of 4WD back into 2WD the whole truck will shudder/clunk like going over a sharp bump in the road. I crawled under the truck and checked the u-joints etc, there is no fluid leaking either so everything looks normal on the outside. Also everything operates fine....except of course when I disengage 4WD.

winks.....did you resolve the issue and if so what was the problem??

Any help is appreciated, thanks in advance.

--Joe

 

How are your tires? Do you rotate them? Are they all the same size? Not rotating them will cause a slight binding in the driveline while on dry roads and in 4wd. Also check your case fluid.

 

Joe, I did resolve the issue. Quite a while after I created this thread, I noticed gear oil leaking like crazy from my front axle housing. It turns out that the front driveshaft managed to elongate the housing to the point where it started leaking fluid. The result was that I had to get a whole front axle setup installed. After I changed it out, I haven't had the bump anymore when switching back into 2wd.

 

I am religious on maintenance, rotate tires every oil change (5,000 miles). Aside from that I just put 4 new tires (all identical) on the truck 2 weeks ago.

I will double check the case fluid, thanks.

--Joe

 

Oh man, that is not what I wanted to hear. Although I do not have any leaking at all under my truck (knock on wood). I will keep a close eye on things.

--Joe

 

Just checked the fluid level in the transfer case and it was perfect, exactly at the bottom of the fill hole, and the fluid looks fine and there is next to no slop in the front driveshaft. I am going to check the front diff fluid level but I can't see that being an issue since the problem only occurs as 4WD disengages.

One thing I did note on my drive home though, is that when I turned off 4WD, I could still hear the transfer case exactly up to the point where the thud/clunk occurred, then it was silent. Almost as if the truck is "stuck" in 4WD until the episode occurs.

Also I will note there is a very small amount of fluid on the driver front axle shaft hub, there is so little that none is even "slung" off of it. In my opinion, with 140,000 miles on the truck that is perfectly normal and is a non issue.

Could this issue be a vacuum problem (not releasing 4WD).

--Joe

 

01 and up trucks have live axles. Meaning no hubs. Nothing on the 4wd system runs off of vacuum. Have you ever changed the case fluid?

 

its not abnormal every 4wd truck ive owned has done it from time to time. hell my 05 F-150 just did it the other day. it even says in the owners manual you may experience a clunk or ratchet sound when engaging/ disengaging 4wd. it wouldnt hurt to give your drivetrain a good once over just to be sure but i wouldnt be alarmed by it.

 

The more I think about this, can you explain what was involved with your resolution?? What exactly was damaged in the front axle? I don't see how the front driveshaft can elongate the housing, causes an entire front axle to be replaced.

That cast aluminum has very little strength, so instead of elongating I would think it would just crack.

Just trying to understand the issue better, thanks.

--Joe

 

Good to know, thank you. I have not changed the fluid, although in light of the situation I might as well. I seldom use 4WD, only in winters when needed due to snow, so while the truck has "high" mileage, the 4WD system does not. The truck has never been off road or even in deep water....just a pavement pounder.

--Joe

 

I checked the front diff fluid and it was spot on as well, although I still think this is a transfer case issue.

So reading what n3elz and whippersnapper are saying........is it correct that the mechanism which engages the transfer case is that electronic module on the rear of the transfer case, next to the damper??

If that is the case, I called and spoke to my buddy, who I buy all my parts from at the local dealership, he said they sell the **** out of those units come winter time. He said it is a very common issue for those to fail.

Thoughts??

--Joe

 

I'm not sure exactly what happened in my situation, I did a lot of wheeling in mud/sand, so I'm sure that did not help. I was told that there was nearly 1/4" of play where the driveshaft came into the axle housing. The truck has been to two trusted mechanics since, one of which actually pulled the front driveshaft, sent it to a place that specifically works on driveshafts, and got a bushing or something like that replaced near the transfer case. Nobody has said anything about the driveshaft being worn or cracked. So what actually transpired, I have no idea. All I know is that there was a major leak, I changed out the entire front axle, and it's all good now -no more leak and no more clunk.

 

When you replaced the axel was it the axel shaft or the gears inside the front differential, im having the same issues with my ranger

 

Hi,
I am experiencing the same problem with my ranger. 140000 km's. A couple of things have come together to make me speculate what the problem is. Just did a long drive and havn't used 4x in awhile. Then i put new tires on the back same size and i checked the circumference of them same size but they are different by 1/10 of a ft, so really that should be in the parameters of wear for the the shift on the fly to work. Also it just snowed here and I am in and out of 4X all the time now. I just changed the fluid in the Transfer case and without taking it apart im not gonna know. Any way the situation is the same as the first post goes into 4X fine but comes out with a loud clunk after being locked in for 200 to 500 ft down the road. The only time this doesn't happen is when I carefully stop and take it out of 4X i think with no pressure on the train or find some big potholes while it is locked in 4X

has anybody had this situation before...
was it different tires, wear
or was it BS with the transfer case?

Erik