clunking noise in 4wd in a 02 f150

[96trigger]

Hi all,

My father in law has a 2002 f150 with the triton 5.4L, manual 4wd shift. Upon shifting into 4wd, the 4wd locks in but upon acceleration, there is a clunking noise in the front end. He took it to a mechanic that told him the front differential had metal in it and was shot. He told him this was common problem in the f150 and would run him about 1,000 to fix replace/rebuild it. I did a search for the "common problem" and couldn't find any other complaints with this problem. All the problems with 4wd in the f150's seemed to be vaccum related.

CV shafts and seem tight, problem only occurs in 4wd. Left my driveway in 4wd, went down the highway a hundred yards, took a left turn, accelerated and had 3 clunks. Thought maybe it was 4wd binding on the pavement. Got on a gravel road covered in snow, tried it again, same problem at low speeds going straight and while turning. Seems like the 4wd is jumping. Any ford experts out there have any ideas on this? I am having a hard time believing its the front differential when there is absolutely no other web information on this "common differetial problem"

[spearchucker]

Sounds like maybe a hub isn't engaged properly.

[96trigger]

Yeah, my first thought was that it was a bad shaft. Apparently they are fine. I have not had time to do a thorough check. When he took it in, I really didn't think they would come back with the differential story. I want to do some preliminary diagnostics on our own to see if theirs plausible, but so far, I haven't come up with much on any of the ford sites.

[spearchucker]

There is no way they could come to that conclusion without opening the differential up. My guess is a bad hub.

[96trigger]

Doesn't have locking hubs, has a front differential and cv shafts, they always turn, but don't always have power. The differential is turned on using vaccum lines and selenoids. I think they pulled the plug on the differential and saw some metal, which is common. Does anybody have any experience with the vaccum system on the fords? I really think it is a vaccum problem, not a transfer case problem.

[jeffreyd]

but it should still use a spring in the hub to lock up. sounds like the hub is bad or has a broken spring in it. one thing to try is have someone walk along the truck to see if they can hear what side and a location. good luck

[96trigger]

Jeff, I'm not sure, I am a chevy guy and am not too familiar with fords, which is why I am here, from what I have gathered, there is no locking in the hub. The cv shafts always spin with the hub, but don't have any power until the differential is engaged by the vaccum system. The differential locks, not the hubs. Again, I could be wrong. For what its worth, the clunking seems to be coming from the differential, not one of the wheels, but I plan on jacking up the front end and doing some more inspecting.

[spearchucker]

I know you don't have a manual lock hub, but there is still an auto locking hub on your truck that is probably the problem.

[Macgyver55]

Correct me if I'm wrong, but I thought the 97 to 03 didnt have the auto hubs. Maybe I'm getting senile....

[fishing tech]

They have a vacuum operated shift fork on the right side axle. There was an update on them I think for not engaging.

[96trigger]

Everything that I am reading is saying that they do not have a locking hub. The CV shafts always spin, but don't have power until the shiftfork, that is vaccum operated, allows power to the cv shafts. The manual shift lever locks in the transer case, and an electric switch at on the case sends power to the vaccum selenoids, engaging the shift fork for 4wd. The shift fork seems to be a common problem as there are plastic tabs/guides, that break off of the fork. Right now, I am betting that his shift fork has broken tabs/guids, and its slamming in and out of 4wd, but its not the front differential. I'm thinking the question is whether or not the shift for itself is bad, or if there is a vaccum problem causing the shift fork to engage and disengage repeatedly while driving in 4wd.

[spearchucker]

Correct me if I'm wrong, but I thought the 97 to 03 didnt have the auto hubs. Maybe I'm getting senile....

You are correct sir. As previously stated the vacuum operated shift fork might be bad on the front differential. You could manually apply vacuum to the line and see if it bleeds away to check for leaks.

[mechanico]

Hey!

I have an '03 f150, and it had a lot of these problems. I was afraid I'd have to replace the infamous shift fork in the front differential,but turned out to be bad vacuum hoses. The solenoids are on the fire wall, same side as the batt. The vac. resivoir is behind the battery. So you have to take the battery and battery holder out, then unbolt the resivoir and you can trace the small plastic hoses. The one to the vac motor on the differential goes under the engine, but it's not too hard to see. BE CAREFUL with the one going truough the fire wall. If you break it off you have to take part of the dash out to get to the other end of it. As for the clunking noise, my book says that some of that is normal, but I wouldn't expect it to be very much, or very long. Mine just does it when turning on mixed dry, wet, and ice conditions. The worst problem is how hard it is to shift it into 4wd, so I'm gonna try the suggestion about spraying it down with penatrant.

Good luck!