I dont think i need any friction modifiers in my 23x,xxx k`s old diff, i have given it a fair old hiding and done a bit of towing with the car as well, and its parts move around very freely in diff casing...... the special fuel efficient gears
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lsd was on strike doing union rules about 5 year ago , its been a single wheeler in my bus for a long time ,
im just about due for rear wheel bearings as well, probably suspension bushes etc as not one thing has been replaced in the back end other than one set of wheel bearings(love my old falcon ).
i have some of the lucas oil stabilizer (the sticky stuff) that im going to wack in it soon just to see if it quietens down the back lash a bit, surprisingly the diff itself as far as gear noise still sounds not too bad for 15 year old car, but the back lash in the diff on gear changes is noisier than a mother in law in the passenger front seat.