The motorcraft. It's like 6 bucks at the dealer and from what I've read it's the best stuff. Even Chevy guys use it.

 

Good deal! Thanks a lot , I'll stop by today and pick some up , and add it in

 

Picked up a Mag cover also, 113K on the truck so it is time. Did you guys really pay $20 a bottle for Mobil 1 75/140 and use 2 bottles of the modifier? I thought all of these new synth gear oils already have modifiers in them. I am gonna keep at my research because it isnt worth doing this and not being happy but I guess worse case scenario is add a bit of FM if I am not happy with it.

 

I hate to tell you but it's more like $17 a quart at the dealer for 75W90. The 75W140 is about the same price. And I get employee pricing at Ford.

Wayne

 

Uh, I think he was talking about the Motorcraft Friction modifier at 6$ a bottle...make sure you get the pointy bottle cap too, makes it easier to squeeze into the rear diff.

 

If you buy the mobil 1 online at advanced you can use the coupon code and save 15% and pick it up at the store. It was 18.99 to start minus the 15%. And yes I added the 2 bottles of the friction modifier also. From what I've read even if the oil says it is included guys have had issues so I talked to my friend at Ford and he told me to just add the 2 bottles it can't hurt it. No problems since the cover change.

 

I developed some chatter in my 3.55LS diff so I changed to RP 75w140 and did not add any FM. I did not have any chatter at first after the change, but it came back. I added on bottle of FM and it went away for a while, but is beginning to do it a little bit again. If folks are adding 2 bottles I guess I can add another one. Don't know why RP says it's not required when it appears to definitely be required.

 

I used Valvoline 75/140 full synth for $13 a quart and 8oz of Champion FM. I avoid the dealer for everything. Same aholes who told me I needed a new long block for $8grand when a simple electrical fix was needed.

 

Chatter is essentially the buildup and release of energy between the differential clutch packs during operation. This phenomenon often occurs when torque is transferred between the clutches or when rotational speeds change. During the stick-slip phase, energy is built up to a point where contact between the clutch plates change between static friction (stick) and dynamic friction (slip), resulting in noticeable vibrations. It is this vibration that causes an audible chatter or ratcheting to be heard within the differential. While certainly an annoying characteristic, there is typically no mechanical damage occurring to the differential. It is most often noticed in parking lots or slow driving while turning where the outside wheel turns faster than the inside wheel.

In an effort to control this chatter, friction modifiers are often used. These additives result in a smoother transition between the two states of friction: static and dynamic. Static friction occurs when the clutches physically lock together, while dynamic friction occurs as the clutches are slipping, ergo Limited Slip Differential.