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.

 

could be a few things. if your mechanic has stated you need a new front diff. and its a common prolem/repair, i would probally loose him as an auto mechanic. narrow your problem down by starting with the u joints first. now when you say manual shift you mean 4 wheel shifter on the floor, correct? imo you should not be going down the road when shifting into 4 wheel drive, see if you have the problem shifting the truck in nuetral with the truck not moving.

 

Ive always shifted into 4high (elect) on the fly, even sometimes at high speeds. Never an issue. Have done it in many other vehicles also and have seen it done manually. Some may say different. 4 Low is a different story.

 

This is a shift on the fly 4wd system, as the manual says. I'm going to jack up the front end, put on the park brake, put it in 4wd and try and turn the main shaft from the transer case, and the wheels by hand to see if I can find out whats happening. Does the engine need to be running for the vacuum system to work. Will this work in park, or should it be in neutral. Any thoughts. Thanks again

 

I have shift on floor floor and have engaged at higher speeds. There is allways a clunk of engage. Four low have to be stoped and in N