2002 f150 auto, with the mnual shift and the 5.4L engine.

There is a clunking sound when shifting into 4wd when going down the road. It sounds like when the 4wd engages, only its making it repeatedly. Mechanic guy said that it needs a new front differential and its a common problem.

Here is what I have gathered from doing some searching on forums. I am leaning toward it not being the front differential at all, but a problem with the shiftfork or the vacuum system that activates the shiftfork. I think the 4wd is engaging and disengaging while driving. I just don't know what is causing it. What tests can I do to see if this is the problem? Thanks in advance.

 

Just from my experience, I had the same problem when placing into 4-hi, it would clink. Come to find out, the driver side cv axle was TOAST! Took the driver side cv axle off, and the bearings dropped right on the floor. Once I replced the driver side, I went ahead and replaced passenger side cv axle as well. No clink anymore and 4wd works outstanding with the recent snow! Hope this helps.

 

I would be extremely cautious with the guy who says its a common thing for the front diff. to go out. You said you had manual shift, is that the tranny or for the transfer case (4X4)? I guess it could be neither, either or both. Perhaps the vacuum front locking hubs are at fault, seems to be lots of write ups about it. Good luck and keep us posted.

 

Thanks guys, I'm going to try and check it out this weekend. Hopefully on Sunday. I'm not sure if its the shafts, but I'll check. Really think its a vaccum problem, or shift fork problem. I don't think its the differential, which is why I am no here asking for advice.

Oh, by the way, its an auto tranny, manual 4wd. Sorry.

 

I'm going to jack up the front end, put on the park brake, and put it into 4wd and see what it wounds like, I'm going to turn the drive shaft by hand and see how that goes, and then the wheels and see what happens there. Does the engine need to be running so the vacuum system works?

 

Front wheels off the ground with the engine running to create vacuum shift into 4Hi and tranny in P. Get under the truck and try to turn the front drive shaft. It should not turn. If it does you have a t-case problem. Rotate one of t he front wheels. The opposite should rotate in the opposite direction. If it doesn't the front axle is not engaging. If everything checks out you have an intermittent problem. It could be the shift fork in the front axle, weak shift actuator motor, vacuum leak, faulty shift solenoids on the firewall or finally a faulty transfer case. Post up your results of the test.

 

thank you JMC, you seem to be the guy that knows the most. I have read plenty of your other posts about this issue but wasn't sure of the exact steps to take. I will jack up the front tomorrow and follow the steps. I'll let you know what the deal is. Thanks a ton, at least now I can try and diagnose it a little better.

 

Jacked up the front of the truck and started it in park, and shifted into 4wd HI using the manual shift lever. Could not move the drive shaft to the front differential by hand. Got our from underneath and turned the driver wheel, the passenger spun the opposite direction. Everything felt smooth and I didn't hear any grinding. Turned the stearing wheel all the way to the right, and spun the wheel, went good at first, then reversed direction and I heard a clicking noise and the opposite wheel quite spinning. You could feel it when the opposite side disengaged. The wheel spun much easier and there was a very noticeable clicking noise coming from the transfer case. Straighten the wheels, and it works good, turn hard right or hard left, and the clicking noise starts and the transfer case seems to disengage. Sound like a bad shift fork?

 

Sounds more like the CV joint. Were the ½ shafts turning when the wheel stopped turning?

 

Do you mean the CV shafts as half shafts? Originally, when I heard the clicking noise, my first thought was CV shafts. The Clicking was definitely coming from the transfer case and the short drive shaft that goes to the front differential was turning when the wheels were spun. The clicking was quite loud and obvious it was in the transfer case, even with the truck running. I can't be 100% sure of the CV shafts, I am only 100% sure that the clicking noise was coming from the transfer case. Its my father-in-laws truck, I'll be able to get another look at it on Wednesday if you think I need to do more.

However, wouldn't it be safe to say the CV shaft was not spinning if it was in 4wd and the wheel quit turning in the opposite direction? Wouldn't it be impossible for that shaft to be turning and the wheel not moving? Why the clicking noise in 4wd?