I have a 2003 Expedition with 252K Miles on it. 5.4 EB. bought it in March of this year. This spring I replaced Both axle fluids, Tranny and Transfer case fluids. In the past couple weeks I've started to hear a "popping" noise coming from the rear I believe. Checked my wheel bearings and no movement, The only thin I noticed up front is I can turn the front wheels have about a 1/2" of play in them when I rotate the tires. In the back my Toe rods have a bout 1/16th to 1/8th in play. Everything else seems tight. Do any of you know what the popping noise could be?

 

Is it a limited slip rear axle and if so did you add friction modifier along with the new fluid?

 

It is Limited Slip. I used Synthetic with FM and added about 4 ounces. I've been trying to figure out if i added to much FM. Some say you can, some say you cant.

 

You can't add too much within reason. Over 100k miles my dealer always used two per change. I did the same when I had LSD and never had an issue.

 

I know its been a while but just wanted to update on what this issue was or at least I believe what it was if some one else starts noticing this. After checking fluids, adding FM eventually the noise went away however a vibration started. Took me a while but i noticed that my front drive shaft u-joints were bad. I have since replaced them and have not noticed the noise and vibration is gone. I believe the popping noise was the U-joint beginning to fail.