Many times on this board I read about people using friction modifier for their l/s rear. One that I found that is very good is Dana part# 43161. It comes in an approx. 6 oz. bottle and can usually be obtained from local truck part distributor that is an authorized Dana, warehouse distributor. I think the bottle usually sells for less than $5.00. Sometimes 1 or 2 bottles will be ample for one diff.

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1999 teal blue f150 s/c
4.6l, xlt, 3.55 L/S
Tow pkg., rhino liner, engine block heater & hard toneau cover. single c.d.
255/75 r16 Generals-owl

 

Gearman,
Just picked some ford FM up for mine. Ford's PN is C8AZ-19B546-A. Yes, it is a 1968 PN. It still $4.50/ bottle.

Tony

 

Fords P# is M-19546-A

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2000 F-150 XL,RC,LB,5.4,4R70W,3.55LS,
Class III tow/Payload #3/Convenience pkgs.,
4-wheel disc/ABS,Chestnut/Parchment 40/60,
Ford bedliner & gas/wheel/spare locks,
3" cold air box modification, Superchip,
Dynomax ultra-flow welded 3" cat-back,
3" exit Y-pipe, Hellwig rear anti-sway bar.