I have a 2005 F250 Fx4 with a limited slip rearend. It makes a vibrating noise when going around corners when it is warm. I added fords friction modifier and it helped some. I have heard I have to change the "clutch packs" in the rearend. Is that true and if so how hard is it to do?

Thanks

 

How many miles are on the rear end? Have you tried replacing the fluid? And you MUST know what your doing to properly replace clutch packs on a limited slip diff, its not something the average shade tree mechanic could or should do.

 

I have not changed the fluid in it. The trucks got 41000 miles on it. It started doing it about 5000 ago. I was going to change fluid, but 75w 140 is $20 a quart. I figured I better find out if that was going to make it better or if I should just have them chaged out. I figured it would probably be over my head to do it.

 

That's pretty low mileage, your diff shouldn't be giving you any problems. Are you 100% sure this "vibrating noise" is coming from it? Just about any differential work is going to cost you a pretty penny.

 

I am pretty sure. It doesn't do it when the truck is cold. If I have driven it about 20 miles it will do it. When I slightly turn it will start vibrating the whole truck. It feels like it is in the rearend when you sit in the back seat. I don't know what else it would be.

 

[QUOTE=1966Ford;3882844]I am pretty sure. It doesn't do it when the truck is cold. If I have driven it about 20 miles it will do it. When I slightly turn it will start vibrating the whole truck. It feels like it is in the rearend when you sit in the back seat. I don't know what else it would be. Also I have put one bottle of friction modifier from ford and it did help quiet it down some.

 

I changed the fluid in the rearend, and put two bottles of friction modifier in. I drove it about 250 miles this weekend and it does it worse now than it did with the original oil and one bottle of modifier.

 

Of course it will. You can't just dump in any old amount of friction modifier, there is an exact amount that needs to be in the oil to make it perform right. The friction modifier does just what the name says, it modifies the fricition coefficient of the gear oil. It essentially increases the friction so the clutchs can grab and not just slip. The more you add the harder the clutches will grab making the vibration worse. You're going to need to drain out the oil and refill with the right amount of modifier in it or else you will for sure fry your clutches.

When you drained it did you see any traces of clutch material in the oil? If the clutches are going bad you're going to see it in the oil.

 

The amount of modifier required in that particular axle is 8 oz, so if you put in two 4 oz bottles, you did it right.

 

My F150 did the same thing. I was told to do some figure 8s in an open parking lot to clean off the clutches, then change the fluid, then do the figure 8s again. Did that and it cleared it right up. After I did a few figure 8s it was a little better, once I changed the fluid it cleared it right up.

 

I put 8 oz's of modifier in. That is what the mechanic at the Ford garage told me to do. I put royal purple 75/140 in. The mechanic also told me the modifier would wear out after 30,000 miles so you have to dump the oil and put new modifier and oil in. I suppose I should have put motorcraft oil in.
I couldn't tell if there was any clutch traces in the oil. The magnet on the plug had some material stuck to it.

 

I put royal purple in instead of motorcraft. The royal purple says it has a modifier in it for limited slip differentials. I prabobly should have just stuck with the motorcraft oil.