Last night I had the fluid changed in my front and rear diffs, the fluid they used (75 90 syn.) SUPPOSEDLY has the friction modifier in it already. I guess I'm just paranoid but, if it doesn't whats the worst that will happen? Also, if I were to add some friction modifier to the rear and it really does have it will it cause any problems?

 

Friction modifier is not necessary for the operation of the Traction-Lok L/S diff. It is installed to reduce customer complaints about clutch chatter while turning.

Many synthetic gear lubes claim that the FM is not needed with their lube. I would try it like it is and if it starts chattering while turning, then put it in. I don't think there would be a problem with adding it to the syn lube in your axle but you should read the label to be sure that there are no compatibilty issues between the synthetic gear lube and the friction modifier (natural or synthetic whale oil).

 

Thanks for the quick reply, it really put my mind at ease! I'll just leave it alone for now then. If I do notice any chatter then I'll try some FM.