I had the truck for two months. I really like it. I notice a rear-end roar around 50-55mph. It was pretty loud. Dealer replaced entire rear-end. The noise was gone for about 300 miles. It is back but not as loud as before yet. I drove a 2002 F150 with 3.55 and it had no noise at all. Is there something wrong with 3.73 in this model? I hate to take it back again especially since they replaced it once already.

Thanks!

 

What's your axle code on your door jamb <a href="http://www.motorhaven.com/">sticker</a>? A letter in the first digit indicates it's an LS unit. Could be someone forgot the friction modifier if that's the case. I've got a 3.73 limited slip and haven't had any trouble. What size rear end?

If it's not done right make them fix it until it is. It's your right ,as a consumer, to get what you pay for. Use that warranty.

-Kerry

 

The axle code is B6. I think I read it was a 9.9 rear end. I do not know what a friction modifier is. I know they had to special order the rear before because it took about a week and had to come on a big truck because it is already assembled. I wonder if there are tolerance problems. I have a 3.73 in my Mustang with 8.8 and never had any issues. They may have the wrong lubricant.

 

Well it must be a 7700 package in order to get the 3;73 gears,thats the only way in a 150 4wd.maybe they forgot the friction modifier additive like the above post said..It comes in a little plastic bottle ..ask the dealer if they added it..Its very simple if thats it..I have a 99 7700 with 3;73 gears and its quiet Yhe other thing to remember is are you sure its not some kind of tire noise? I have brdgestone Duellers on mine and they DO make noise at highway speeds compared to the Good Years on my Off Road 2002 4wd 150................By the way I love the 3;73 gears over the 3;55,s in the 2002 ..theres no comparison..To bad we cant get them as an option..

 

B6= 10.25" semi-floating, limited slip, 3.73 gear ratio. Same rear in my truck: a 2000 7700 4x4.

I still have the factory Goodyears on mine (with 50K miles, so they are getting close to worn out). I have never heard a noise as you describe. On occasion I'll feel a clunk as I round a corner, could be the LS sticking and not fully disengaging. I'm certain that it's tire noise or lack of friction modifier. If you still have the problem after a bottle of that stuff, and you haven't changed your tires, then I'd say you have bad luck with rear ends.

Try the dealership agin, warranty them until it hurts.

-Kerry

 

I have heard that clunk sometimes before too. It is definitely not tire noise. The reason I know is when you lightly press the pedal going 52mph it is a whining noise. It stops as soon as you lift off the gas pedal. I will contact Ford dealer to see if they know what I am talking about with that friction modifier.

Thanks!

 

Hmmmm, you got me thinking about other things in the truck might be making noise, not just the rear. Since the dealer changed the rear out last time, then that must be where the problem was originally. I wonder if you don't have a bearing going out somewhere else in the drive train. A bearing that depends on the axial thrust or forward motion. Could be anywhere from the engine back... what tells you it's the rear?

-Kerry