My 04 4x2 5.4 Lariat was getting about 15mpg on average. This was a mix us HIGHWAY & CITY driving. Recently my clutch packs went bad in my rear end, ford replaced them and now with the same driving condition my truck has dropped to 12mpg. Any help?????? or ideas???????????

 

In your "city" driving, turning corners now tries to sprag the inside turn tire on the turns due to the clutch packs trying to keep the drive to both axles. Same actions that happens on a 4x4 engaged on a dry road causes the wheels to intermittantly break loose when making a turn.
This uses extra engine power to overcome the resistance encountered at those times. The wheels turn at different speeds in a turn and the clutch paks try to keep this from happening so somthing has to give. Either tire traction is lost or the clutch paks slip and wear..
You will probably see shorter rear tire life.
Not saying there could not be other problems but just to address that traction control costs power when not running in a straight line.

 

More likely, they assembled the rear end wrong. Drive for a few miles down relatively straight road. Crawl under the truck and see if the diff is hot. It should be warm but you should be able to leave your hand on it.

If you have jackstands, raise both rear tires off the ground. In neutral, see if you can turn the rear wheels. There should be a fair amount of resistance but you should be able to put both hands at 3:00 and 9:00 positions and turn it quarter turns left and right.

If it is hot or binding, ask the shop to check their work.

 

Not to sure of everything that you are saying. My truck is 4X2. And not sure why I would have problems now with my gas mileage...before the replacement clutch pads were put in I got 15mpg and after the clutch pads were replaced the mpg dropped to 12. I don't understand the drop in gas milage.

 

It would probably help them explain in a little more depth if you specified which parts of their posts you're having trouble understanding. I'd take cantrma's advice and feel the pig (large round part of the axle) after driving it for a while to see if it's warm, and try out the binding check.

 

I had a friend of mine ask a guy that works for a local dealer and he told me to give it a few hundred miles because gears need to break in. Does this sound right?

 

Technically there is a breakin to new gears.
They are ground in and have to slide across each other.
If they over heat at the rubbing surfaces, the hardening process will be uneven with various results.
They should have told you about the breakin.
Usually light load accelerations for about 10 miles several times, then let cool and do it again a couple more times with cool down between. After about 50 miles it should be safe to load the gears with WOT acceleration or pullling without a problem.
All the previous post are applicable to your situation.
My first post is fully valid for any traction lock and somthing all have to live with to get the benifits of increased traction.
If the shop made a huge mistake of putting it togather with no back lash, then you can end up with a problem as it gets hot and makes thing even worse.
You just have to do some thinking and relating.
Good luck.

 

After drving about 70 miles today I got under the truck and checked the rear end for heat. Could put my hand on it and leave it there as long as I wanted...it was warm but that was about it. I have noticed that when I let off of the gas the truck does not seem to coast as free as it did before the clutch packs went bad. It also seems like I have top be in the gas a little more with the motor sounding louder.

 

That's exactly what I was suggesting. They had to do brake work too. They could have adjusted the drums too tight or the e-brake too tight. Do the same thing but stop with only light braking and this time see if either rear wheel smells hot. There is always a faint odor. If there is enough of a problem to feel it slow down, require more power, or have worse milage, it should be very noticable if you stick your nose under the wheel well.