This may sound like a stupid question. Does the friction modifier in the dif oil add friction or remove friction? I talked to two Chevy service techs and one said it added friction, the other said it removed some of the friction in the clutch packs. I think it removes some of the friction to allow the clutch pack to slip while making a sharp slow corner. Don't respond unless you know for sure.

 

reduces friction...

 

i changed rear gear oil without modifier and did peg leg burnouts and launched straight, i changed to royal purple with modifier and added a tube of modifier and now both wheels burn and fishtails

 

Okay, here we go again. Devilish34 says it reduces friction. Dennis50NJ says it increased friction to his clutch pack and kept both wheels turning together. Before he added the friction modifier one wheel would spin as one of the clutch packs sliped. It can't be both, increase friction and decrease friction. I need more input on this. I'm still confused.

 

Decreases friction so the car can make tight turns. Had this issue with an older car with Posi. After long drives the rear axle would become locked and when I pulled off an Interstate the car wouldn't turn without the inside rear wheel hopping up and down. Adding friction modifier solved the problem.

Bill

 

To much friction and you will get chattering in the differential on tight turns.

Tom

 

Does anyone else have an opinion on this subject? I think the general consensus is that it reduces friction to stop clutch pack chatter. If you have a way to confirm this please step in and voice your opinion. Thanks for all your input.

 

Not real proof, but...

Like Bill D, we had older cars with Posi that would act like the rear wheels were fighting each other in tight turns. Adding the GM Friction Modifier would eliminate the problem.

Starting in M.Y. 2009, the Corvette comes with a different diff lube that does not need any additives, in fact using them can cause other problems according to GM. We now have 52k miles using the 2009 lube, changed at 7k and 50k just as a precaution, never any noise or chatter from the diff.

 

I had the chatter problem with my 07 and changing the fluid out with gm dextron ls #88862624 which has the proper friction modifier solved the problem. Based on the characteristics of the chatter where when turning one wheel spins faster than the other causing the wheels to transition between slip and lock creating the chatter I've been of the opinion that the modifier reduces friction. AMsoil has a pretty good write up about their product and how it works which might be of interest. Also, this is what wiki says: http://en.wikipedia.org/wiki/Friction_modifier

Pretty sure the answer is reduces friction.

 

Decent discussion here:
AMSOIL Slip-Lock Differential Additive (Product Code ADATB)

Diff chatter is caused when the diff clutch plates grab and release (chatter) vice sliding smoothly over each other when there is relative motion between the plates, such as would be experienced in a tight turn when the outside wheel, and hence the diff clutch plate on that side, is spinning faster than the inside wheel (clutch plate). When the fluid doesn't allow smooth sliding of the diff clutch plates, adding more friction modifier should reduce the friction and allow them to slide smoothly over each other.

For the street, this is probably a good thing as most do not like to hear the diff chatter. At the track or drag strip, this is counter productive as in high performance situations the limited slip diff will work best (most torque to the tire with grip) when there is more, vice less friction, between the plates. For example, when coming out of a hairpin corner where the outside tire is loaded and thus has all the grip, in a completely open diff all the torque would go to inside unweighted tire and you'd see the typical inside tire burnout which doesn't help move the car down the track. In a completely locked diff, equal grip would go to both the tires, thus the outside tire with grip would get half torque vice about no torque as in an open diff. So to keep your limited slip diff more like a locked vice and open diff, you'd want the least slip possible (e.g. most friction between the plates). Trade off of performance vs. daily driving suitability.

Not sure about the spec on the C6 diff, but in my C5 the limited slip diff spec is 75 lb-ft, or only about 25% of the torque on my 02 Z06. This is something I check fairly often on my track car. I left one rear wheel and with the car out of gear put a torque wrench on the axle nut and see how much torque is needed to spin the wheel. If it is well below 75 lb-ft, time for me to rebuild my diff.

 

Went through a lot of clutch discs, pressure plates and a flywheel on an older GM car years ago because the Posi was chattering and I could not get smooth starts without slipping the clutch. Finally a mechanic friend suggested I drive it in a circle slowly and you could feel the car wobble as the posi grabbed. Added GM Friction modifier,(think it had whale oil in it in those days), and no more problems. Funny how some things just never change.

 

My concurrence. Too much friction modifier disables the positraction functionality.