What is Posi additive, what do they mean by "friction modifier"? Why do you need it with Posi rear ends? Can you use to much? Will using more help a worn posi last a little longer? Thanks. -Jeff
It's only used on clutch type limited slip differentials. Posi additive is to make posis quiet. It actually helps them slip, so it won't help a worn out posi & will probably hasten its demise. I don't use it. I do soak my clutch plates overnight before assmbly, but that's about it. Road racers swear by straight gear oil - no additives. They say clutch-type posis last significantly longer. However, most of them burn clutch types up, so run torque sensing lockers like gleason-torsen or auburn(?).
The original GM oil was made from sperm whales. The gov't made them discontinue it in the '70's. Not sure what part of the whale was used, hope it wasn't the sperm.
Like mentioned, it is used on clutch type posi's when they start sticking and making it jerk around corners. It makes the gear oil slipperier (is that a word?) to the clutch discs, so they won't grab and release causing the jerking. Will not help a worn out posi, besides making it slip easier. Has no effect on the gears as far as I know. The GM stuff was made from whale oil, and is not available any more.
GM does make a "limited slip additive" still....p/n is 1052358...it runs about $7 retail...not trying to spam there guys...just what it costs over my counter
Since you are using the term "friction modifier" im guessing you talking late model Ford stuff? If you are, Yes, you do need it. It will make it feel like a tire is rubbing a fender when making tight turns like in and out of parking spaces.
The origional GM Posi additive was developed because owners of positraction equiped cars were complaining of chattering rearends when going around corners. The additive allows the clutch plates to slip thus negating some of the "positraction" effect. The old time drag racing "speed secret" was to drain the rearend and add straight gear lube. You got the chatter back but you also got better lockup in straight line acceleration. Frank
Ford or napa sells it, it comes in a LITTLE bottle and smells really bad, it costs about 5 bucks, it won't hurt anything, try it.......... LUKESTER
[ QUOTE ] what would happen if you used it in a NON posi rear end? [/ QUOTE ] nothing would happen other than wasting money.. like the others said..with out it you will have noise or popping on turns..
[ QUOTE ] Go to Lucas Oil, they have a product that works better, I know. [/ QUOTE ] Are you referring to Lucas' Oil Stabilizer (the thick stuff like honey)? Or another product of theirs?
Ford took away the bad smell . I'm serious. Thats what they told me at the counter last time I bought some, and they were right.
[ QUOTE ] Since you are using the term "friction modifier" im guessing you talking late model Ford stuff? If you are, Yes, you do need it. It will make it feel like a tire is rubbing a fender when making tight turns like in and out of parking spaces. [/ QUOTE ] It only quiets this & allows better slipping of the clutches. It's still less noise & banging than a detroit locker & if you're after traction, I wouldn't run any. Friction modifier = LESS friction. So even in the Ford trak-lok it's only a WANT & not a NEED. If you WANT it to be smooth & quiet, get it. If you NEED traction, bin it.
My understanding is it's more like a break in lube, to get the clutches to seat properly on a new setup. I never use the stuff unless it's a fresh set of clutches, just standard gear lube. I agree with Flat Ernie, using more of it will cause the clutches to slip even more, that's how it cuts down on the noise.
So if I put straight gear lube in my very worn non-rebuildable Auburn cone type limited slip, it might not slip as much, but may make a little noise going around corners? At the very least, it's worth a try and won't hurt anything, right?
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