Every since i had a mechanic at the local Amoco i ALWAYS go to change the rear differential fluid, the limited slip locks up way too early. I had him change it again and make sure he had the special additive the limited slip needs. But it still does it, the tire doesn't jump up the ground but i locks up pulling out of parking spaces. Any advice is REALLY appreciated. thanks

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1998 Black F-150 5.4L Lariat with ORP
GTS Blackouts Front and Rear, GTS Wind visors on windows and bug deflector

 

Ford did issue TSB for a "tightly" gauged clucth pack within certain limited slip rear ends mfg for 98 models. My suspicion: your local mech did not add the required 4 ozs of friction modifier. I would go to dealer and buy two bottles and pour them in your self. Ask for the nipple cap that can be cut and add small rubber hose to it for easy servicing.

Bob

 

If it was fine before the change, and messed up after, your first place to look should be what they did. What was the "exact" type and amount of oil and friction modifier used? If you don't know for sure, drain and refill with "exactly" what is specified first.

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2000 F-150 XL, RC, LB, 5.4L, 4R70W, 3.55LS,
Class III tow, Payload #3, & Convenience pkgs.,
4-wheel disc/ABS, Chestnut/Parchment 40/60,
Ford bedliner w/Paintsaver & gas/wheel/spare locks,
K&N F.I.P.K. w/Outwears pre-filter, Superchip,
Dynomax ultra-flow welded 3" cat-back w/ 3" Y-pipe,
Hellwig front & rear anti-sway bars, Rancho RS 9000s,
Mobil 1, K&N oil filter.

 

I had a similar problem with my LS. It turns out that the clutch packs were assembled wrong from the factory. I had a shudder from off the start (0-5mph).

The fix was to replace the clutch packs, back lash, and back face (according to the work order). Luckily it was still under warranty, so I got it fixed for free.

I hope that can be of some help.


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1998 F-150 XLT 4x4 SC/SB 4.6L, Auto., 3.55LS, TTP, blah, blah, blah
All the info is at http://www.fordf150.net