80W-90 GL-5 differential gear oil questions

Discussion in 'Got gears?' started by buick64203, Feb 20, 2018.

  1. buick64203

    buick64203 Just plum crazy Staff Member

    Once again Im overthinking stuff. I need a sanity check. Im replacing the gear oil in my 8.2 limited slip diff....

    I bought AC Delco #89021669 80w-90 GL-5 Hypoid. Says its for use in conventional type axles. Naturally not limited slip. So I bought the AC Delco LSD additive in addition.

    In the past, Ive always used Valvoline 80W-90 "Limited Slip" GL-5 gear oil and the additive in addition. But the limited slip oil just has the additive built in right? So is it a waste adding additive to the LSD gear oil?

    Is it six 0f one and half a dozen of the other? Does it really matter?
  2. Mart

    Mart Gold level member

    I always use the additive. This combo right here.

    Attached Files:

  3. pbr400

    pbr400 68GS400

    I’ve heard it’s one or the other, not both. Don’t add LSD additive to fluid with it already; it’ll be too ‘loose’.
  4. Mart

    Mart Gold level member

    I've never used the GL-5 already labeled as limited slip. This GL-5 is heavy duty synthetic extreme pressure lube. No mention of LSD.

    Got the new grape scent which is a plus!:)
    300sbb_overkill likes this.
  5. buick64203

    buick64203 Just plum crazy Staff Member

    I filled up the diff with the Delco 80W-90 hypoid with the additive today and went to a parking lot and did some figure 8's. No chatter. Did a quick oil change and filter, topped off the gear oil in the Muncie with some GL-4 and put 12 gallons of fresh fuel in her. She's ready to go. Thanks for the advice guys
  6. BrianTrick

    BrianTrick Brian Trick

    Do NOT use synthetic gear oil with ANY clutch style posi unit.
  7. buick64203

    buick64203 Just plum crazy Staff Member

    That's kind of a blanket statement. Why is that? Redline specifically recommends their synthetic for clutch type posi's

  8. Dwayne B

    Dwayne B Well-Known Member

    I'M A big believer in GM gear oil and limited slip additive .I had A bad experience with Lucas gear oil one time in new diff.
  9. monzaz

    monzaz Jim

    THIS IS WHY....

    This product is not designed for use in most manual transmissions or transaxles in passenger vehicles, since the extreme slipperiness may cause synchronizer mesh issues that lead to shifting problems

    This will cause the same trouble in a CLUTCH or cone style FRICTION base posi unit...IF you have a real tight posi and want to kill some of the tightness...then yes use it. If you want the posi to be tight then DO NOT use synthetic red line

    we recommend the RED LINE limited slip ADDITIVE ...IF your posi unit is way too tight...It quiets the clutches and cones very well. like Pro type units with heavy preload pressures.

    J D RAce
  10. buick64203

    buick64203 Just plum crazy Staff Member

    Good info Jim. They really ought to state that specifically on their site
  11. monzaz

    monzaz Jim

    Well for most people it is not a big deal nor do they understand anyway so why try... It really should destroy any parts...But in steel clutches it helps to quiet down the chatter that happens between metal parts. The reason Brian and I do not recommend is because WARRANTY of Eaton and Auburn will not stand behind synthetic fluid in the rear. That is their rule for warranty.
    SO if you do not care about that or the unit is over a year old out of manufacture time frame...give it a shot.

  12. buick64203

    buick64203 Just plum crazy Staff Member

    You learn something new everyday. As a rule, I try and stick to whatever the manufacturer recommended. Keeps me out of trouble. Even when it comes to our old stuff.
  13. BrianTrick

    BrianTrick Brian Trick

    You will get a little card inside the box of any new posi unit,with the warning about the synthetics.
    Maybe it would be better to say that you can run synthetics in a Tru-Trac or spool.
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

  15. Mart

    Mart Gold level member

    Gear shop that installed my Tru-Trac said either was fine in it. He's the one that will have to warranty it!
  16. monzaz

    monzaz Jim

    Ha Ha warranty...That is a good one. You guys that ask about warranties are funny. ALL the small print you will see how good warranties are.
    Just do your home work before you take it to any shop first. ASK A LOT of questions and if they do not have the time to explain what answer are...Then do not think they are going to spend 1 second of time in warrantying anything for you.
    Plus warranty does not include the price to install and reset up gears and anything else that get taken out. SO... be careful and do homework and recommendations.

    Good luck.

    Oh true trac does not have cones or clutches that is why you can use synthetic... same with a spool NO moving parts at all.

    J D Race
    Mart likes this.
  17. Mart

    Mart Gold level member

    Hey, you get a case of synthetic for free from your bud, then you have no choice but to buy the Tru-Trac.:D
    300sbb_overkill likes this.
  18. monzaz

    monzaz Jim

    As I always say.....IT IS your vehicle always.... We are just here to help and guide...You are free to do what you feel is correct, always. :)

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