Limited Slip Additive

Discussion in 'Got gears?' started by Carcrazy, Mar 14, 2017.

  1. Carcrazy

    Carcrazy Dan Whytock

    If your running a factory 3.64 axle should I be adding a 4 oz. bottle of limited slip additive when I change the oil?
    No one has ever mentioned this to me before. All I've been told is don't use GL5 or synthetic oil
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I always use the additive in a Posi.
     
  3. BrianTrick

    BrianTrick Brian Trick

    Use conventional oil,not synthetic,unless you are running a unit like the Tru-Trac. Yes,cone & clutch style posi units require one bottle of additive.
     
  4. Smokey15

    Smokey15 So old that I use AARP bolts.

    I put Royal Purple in the new (haven't driven yet) Auburn posi 12 bolt in wife's Z/28. I've heard both "Don't use it!" and "It'll be fine."
    I do add Ford or Chevy posi lube to diff's with regular gear lube and to all 3 and 4-speeds.
     
  5. BrianTrick

    BrianTrick Brian Trick

    There should have been a "warning" tag in the box with the posi unit,about not using synthetics. The synthetics are more slippery,which makes it harder for the posi unit to function properly.
     
  6. flynbuick

    flynbuick Guest

    The same is true for 4 speed trans. Some major rebuilders give warnings to never use synthetics in 4 speed trans.
     
  7. deluxe68

    deluxe68 Well-Known Member

    Could one just use Lucas "non synthetic" heavy duty / high performance gear oils?
    It has the anti wear and limited slip additive already in the bottle. They claim, no extra additive needed.
     
  8. Guy Parquette

    Guy Parquette Platinum Level Contributor

    Which is odd, because that is exactly what the friction modifier does. It helps the clutch packs slip so as not to tear up the fiber material, and keeps it from "chattering" when cornering.

    So, would the cone style not use friction modifier, being that its metal to metal?

    We need a specialist to step in.

    Monzaz, are you out there???
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  10. sriley531

    sriley531 Excommunicado

    I run Brad penn conventional and a bottle of gm performance parts additive in my eaton equipped rear end. I actually run Penn in my muncie as well fwiw.
     
  11. BrianTrick

    BrianTrick Brian Trick

    Thanks for posting that Larry. Auburn has a very similar tag in the box with their posi units. I think theirs also state that the use of synthetics can void warranties.
     
  12. flynbuick

    flynbuick Guest

    We have seen this tried before and the GM additive was still needed before the rear operated correctly. I cannot recall the brands of 90 weight oil used but this has come up several times since this Board has been operational. I had a personal experience with this myself.
     
  13. gstewart

    gstewart Well-Known Member

  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    You're welcome Brian. I bet lots of guys never notice that card.:grin:
     
  15. Smokey15

    Smokey15 So old that I use AARP bolts.

    I never saw the card. A friend set the diff. up. Looks like I pull the plug and replace the lube.
     
  16. BrianTrick

    BrianTrick Brian Trick

    When you,ve been doing it for over 20 years,and built over 1,000 rears,you tend to notice a few things.

    There have been topics about the clutch chatter,and I have responded with some posts,and links on how to properly tune a clutch style posi unit. The clutches chatter because they are trying to disengage,but you have that spring pack in there,pushing them together.They don't need to be engaged all of the time.By tuning the unit,you shim the clutches properly,leaving no play or slop between the side gears and spider gears,and you pitch the spring pack in the can.This allows the clutches to disengage while cornering,and when under stress,the side gears and spider gears push on each other,pushing the clutches together.Eliminating the slop also puts the gears deeper into each other,where they are stronger.
    Tom's Differentials did a good video,showing this.
    If you also notice,the newer clutch units come with stiffer springs.Why? Because the clutches are not as aggressive as the original style,so they need more pressure to get them to work. The original style clutches were all knurled steel,so you had each of them pushing against each other,and could work pretty good,even in production form.Now you have some polycarbonate gimmick that mates against a smooth steel plate.They tried to make something that was smoother for cornering,but lost the aggressiveness,so they stuck a stiffer spring pack in there.It doesn't take a lot of common sense to see which is better. Use the good knurled steel clutches,shim them properly,eliminate the spring pack,and you will have one very nice unit.
     
  17. deluxe68

    deluxe68 Well-Known Member

    I followed this sheet that came with my unit.
    Installed (2014) and currently there are absolutely no problems.
    however, I did not​ use synthetic fluid.
     

    Attached Files:

  18. BrianTrick

    BrianTrick Brian Trick

    What unit did you get from Jim?
     
  19. Guy Parquette

    Guy Parquette Platinum Level Contributor

    Most all later model vehicles use synthetics in there clutch packed differentials...

    I've had synthetic in my Brute Strength 12-bolt Strange carrier in a Ford 9" housing since the mid 1990's. And everything still looks and works fine.
    Granted, it gets little use than a road car, being its a drag only car...
     
  20. deluxe68

    deluxe68 Well-Known Member

    JD Race 10 bolt 8.5 Eaton Detroit TrueTrac posi / 3.42 gears
     

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