I have a strange popping/rubbing sound coming from my 99 expedition when I place it in 4H or 4L. It made the sound right from the get go either in a straight line or turning. I thought it was the cv joints but after looking at them figured it wasn't.

I have replaced the transfer case oil and the rear diff plus put in 3 tubes of friction mod. This has seemed to help some but the sound still shows up under hard acceleration in a straight line or once the truck gets up to speed, then it sounds like a pretty constent knock until i let off the gas. When I let off the gas it makes a erratic knocking sound then will go away until i build up speed or turn. When in 2 wheel I have heard the sound maybe twice but it was while turning and that was it. Mind you this has all been in the snow/ice so far to date.

Is there anyway to determine if its the transfer case or just a crappy diff? I am out of ideas so any input would be great, thanks guys!

 

Remove fuse #104 from the under hood power box. Then see if the popping goes away. If it does it could mean that your tires have not worn evenly. If it doesn't go away then you might have an issue with the drive chain inside the transfer case.

 

I should have mentioned it has the brown wire mod, so the clutches are not being used. If it is the drive chain how can I go about checking that and what is the parts breakdown. I have a haynes but that dont say crap about the transfer case! Thanks, I am really hoping it isn't the transfer case, but who knows!

 

You're going to need a factory service manual for information on the t-case.