Okay guys, I'm singing the Ford limited slip blues, again. Bought our truck in April of '12 and got a pretty good deal on it. It had 31,000 miles on the clock when I bought it and I replaced the 3.73 LS gears with 4.30 gears almost immediately following purchase. Since the truck had some warranty left the local dealer warrantied the limited slip clutch pack at the time of the gear swap since the LS with the 3.73's wasn't working at all so the LS clutch pack that went in with the 4.30's was brand new.

Following the break-in procedure I changed the fluid after the first 100 miles following the installation of the new ring and pinion. At that time I put in full synthetic with a half bottle of Ford friction modifier. The full synthetic fluid had friction modifier in it and that's why I only used a half bottle of the Ford stuff. I've put about 4000 miles on it since the differential break-in fluid change following the regear. I broke the tires loose on a tar and chip road yesterday and only the right rear left a black mark.

I can't believe the clutch's are worn already so I'm thinking I may have too much friction modifier in the fluid.

The question is, if I drain the fluid and put in fluid that has no friction modifier in it at all will the new clutch's hold? I figure if they do hold I can add the Ford friction modifier until it quits chattering. Or, did I already screw up the LS clutch's that they will never hold again. In which case new fluid is a waste of money.

Thanks for the feedback.

 

I cant say if your Clutches are bad but i have a hard time believing it...
I will say i do NOT buy into Ford's "snake oil" after what i experienced

I changed my Gear Oil shortly after buying my truck & the Valvoline Full Syn i purchased said it did not need an additional friction modifier BUT the dealer said yes it will. After asking if i could "over treat" w/modifier if it was included in the oil already, i was told NO. So i added 1 bottle & after about 2 months (i drive the truck very little) the Axle started "chattering" while i was backing up (if the 5'er was attached) & also anytime i would really put my foot into the throttle...

After talking to a friend of mine who worked at a Ford dealer, he said they soaked the clutches in that additive to "soften" them prior to installation.
Which got me to thinking that with all that additive i was wrecking my clutches
So i decided to try something....I drained the axle fluid & refilled only with Lucus 75w140 which does NOT require any additives.
I've always had good luck w/Lucus products with half whipped or modified vehicles.
It worked
I have even pulled the 5'er to Michigan & never felt any chatter, nor do i feel it while accelerating under my heavy foot & yes it will still lay 2 healthy black marks on the highway

Short & Sweet....I'd refill w/a quality fluid (ie: Lucus) & forget about the "snake oil" after u get em working
BUT if u dont feel any chatter & it only leaves 1 black line, it seems as if there no good but IDK for sure....Let us know the outcome & Good Luck

 

I was thinking the same thing. Common sense would lead one to believe that in less that 5000 miles the clutches would probably not be worn enough to be worn out already.

One question, did both rear wheels spin on pavement prior to putting the Lucas fluid in the differential? In grass or gravel both of mine spin but on pavement of any kind they don't.

I've read and heard so many bad things about Super Duty limited slip systems that I kinda' wish I'd have spent the money on an after market LS system when I did the regear. At the time letting the dealer warranty the stock clutch pack seemed like the thing to do and it was the cheapest for sure. Not sure it'll be the cheapest in the long run. I pull this truck hard almost all the miles that go on it. I'm pulling loads out in fields, etc., and really need as many wheels pulling as possible.

 

the friction modifier makes the diff "slippier". so you aren't going to damage the clutches by adding too much modifier. you are simply defeating the limited slip

I recommend you change oil out with whatever brand you have locally. I used valvoline 85w145 with the friction modifier already added. my LS is working great at 78k with the new fluid. fluid cost me <$30 as well

 

Yes, mine has always left 2 black marks (so far anyway)
Its just after i put that Aluminum Cover on, changed the Oil (which said it did not require additional FM) & put in Ford's FM anyway.
It chattered while under hard straight line acceleration or if i had a heavy load on (ie: 5th wheel) while trying to back into its spot which is up an incline.
Its been working great w/only the Lucus oil

P.S...Dont know if PowerTrax makes a kit for our trucks but ive installed their kit's in 2 of my previous trucks (supercharged S10 & a 1/2 ton 4x4), those babys stood up to years of abuse & were easy to install.

 

Which is why mine was Chattering so much....Slipping/catching/slipping/catching

 

The limited slip diff was never designed for doing burnouts on dry pavement. It was designed for limited traction conditions to give you more traction, which from your description it's doing just fine because both wheels spin on grass or gravel.

That's why it's called a limited slip differential, not a locker.

 

Crazy, what you're saying makes good sense and I have no doubt that what you say is the case. I only know that our '06 Ranger with limited slip will spin both rear wheels on any road surface. I don't do "burnouts" but once in a while we'll gas it up a bit too much on a hot country tar and chip road with our '06 Ranger and it spins both rear wheels every time, which isn't often. Did the same with the Super Duty and it only spun the RR.

I just thought I might have over done it with the friction modifier which might have rendered the LS clutches too slick to hold.

I'm intrigued by the aftermarket LS systems available if anyone has any first hand experience with purchase and installation.

 

I believe it Ken, but remember the LSD on that Ranger was only trying to break loose tires on a ~1,500 lb axle. Your Super Duty rear axle weighs twice that much, which is an awful lot for a clutch pack to overcome.