I have an 05 Lariat Supercrew 4x4 with 70k. One year ago I had problems with the rear differential clutch packs.......changing the fluid did not help so the clutch packs were replaced at a local Ford dealership. Not Cheap! 13 months and 8000 miles later, I am experiencing a similar problem, and the dealership wants another $800.00 to "fix" it again. I am considering having a local mechanic change the rear end to an Eaton locker.........any thoughts? I have searched the forum and can find no related topics, so I appreciate your help and/or suggestions...............

 

What type of problem have/are you having with the clutch packs? Have you looked at the Powertrax Lock-Right Lockers?

 

The problem is a rear end chatter when starting from a stop, mostly if there is steering input (which I presume causes each of the rear drive wheels to turn at a different rate of speed). I have not noticed the symptoms in reverse, only when driving forward. I did not know about the locker differential you suggested, thanks much for the lead. When I did my Internet search all links and discussions lead to Eaton, and an on line discussion with a technician at Jegs suggested the Eaton was my solution. Obviously, I want to have the problem resolved, but expense is a concern and I thank you again for suggesting an alternative to research and consider!

 

The chatter your hearing (some people may experience a groan noise) is due to "Stick-Slip". While it is annoying, typically there is no mechanical damage done to the differential. It's a "That's annoying" sound. My 1988 Ranger with front and rear TRAC-LOCs would groan about every 25,000 miles (made a lot of left & right turns everyday to and from work) as I had the pre-load set up pretty tight on the axles. I would drain the gear lube, add new w/modifier and it would be quiet for another 25,000 miles. The clutch packs were still tight when I sold the truck with 196,000 miles on it 13 years later. Never had a tire slip on me.

Anyways...Stick-slip is basically the buildup and release of energy between the clutch packs during turning when torque is transferred between the clutch packs when speeds between the rear tires change. During the stick-slip phase, energy is built up to a point where contact between the clutch plates changes between static friction (stick) and dynamic friction (slip), resulting in noticeable vibrations. It's the vibration that causes an audible chatter or ratcheting to be heard within the differential.

Friction modifiers are normally used for a smoother transition between the two states of static and dynamic friction.

I normally soak new clutch packs for 24 hours in gear lube before installing. I also tend to increase the pre-load tension a little.

You should always make sure that friction modifier is added to the gear lube to help control the clutch slippage.

After buttoning up the rear-end, I take the vehicle for a ride to an empty lot and do about a dozen slow figure 8's to work the clutch packs.

 

Good advice, thank you very much....................I will try that first opportunity I have.

 

No problem...

On a side note...Most people with a L/S axle will never hear any noises because years ago, the MFGs started setting them up with a lighter pre-load because people were complaining about chatter or groaning from the rear on turns. That basically eliminated that problem. So since yours is doing it at such a low mileage, I would consider myself lucky to have a good "Working" L/S axle as most these days are almost an open diff with clutch packs just going for a ride.