Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Buick Rainier, Chevy TrailBlazer, GMC Envoy



  • n7donn7don Posts: 188
    Look for "G80" in the list of codes on the glovebox door. Your owners manual will have the info on what gear oil to use HOWEVER be advised tblazed & I have looked hi & lo for commonly available synthetic gear oil meeting the GM spec listed. We've found none that specifically references the spec. Emails to Mobil1 and Castrol have received negative responses. If you find any please post the results.
  • blink3blink3 Posts: 74
    Thanks for the info. I do have the "G80 code, I thought the G80 code was for the actual gear ratio of the rear end? I may be mistaken. Where might I find a list of what all those codes mean??? Also, I was going to use a redline or royal purple synthetic rear end oil. If it is good enough for a C5 corvette it should be good enough for this. I work in a shop and the redline is what we have been putting in all the vettes lately. Supposedly the GM fluid was garbage. ???
  • polespoles Posts: 23
    this might sound stupid, but what is the difference between having limited slip differential and not having it?
    and, what are the benefits and downsides to having it?
    thank you poles
  • blink3blink3 Posts: 74
    I found it after diggin a while. You are right G80 is Positraction Limited Slip, and the other code I was thinking of was the GT4 code which I have the 3.73 gear ratio. Reason I am checking into this is the "slop" I feel that I believe is coming from the rear end. If you haven't already, could you read my post earlier and tell me what you think?
  • I may be wrong here but I believe Amsoil has a synthetic that will work in this application. Let's say at least I had a dealer recommend an Amsoil product
  • blink3blink3 Posts: 74
    I have used Amsoil in lots of vehicles too. I will research that!
  • blink3blink3 Posts: 74
    I am sure someone will correct me or add more to this but the main idea is that BOTH rear wheels are supplied power versus just the typical ONE rear wheel getting the power. The rear differential in a limited slip actually has a little clutch pack in it that will allow for the wheels to turn at different RPM's while cornering, thus limited slip. A limited slip diff. will take a different lube or at least need an additive added to it versus a standard diff.
  • I am sure someone will correct me or add more to this but the main idea is that BOTH rear wheels are supplied power versus just the typical ONE rear wheel getting the power.

    Both real wheels get power on any differential most of the time. An open differential allows the wheels to turn at different rates to faciliate turning. The flaw is that if one wheel spins, it ends up getting all the power. That is not the intent! If you saw the innards of one you'd see quickly how this happens, but it can't explained without pictures.

    With a limited slip, the wheels can turn at different rates up to a point. Then the cluthes engage holding and the axle is partially locked up. The wheels will turn at basically the same rate.

    Anyway, no triplet has a limited slip.
    The third type of differential is the locker. Too much slip = the axles lock together and the wheels turn at exactly the same rate. Different technology - same basic goal.

    Also, there is a common misconception out there that if you have a limited slip or a locker, you've got twice the traction. That is false because as I stated, an open differential is truly 2 wheel drive. It's only if one wheel breaks loose that it goes to hell.
  • polespoles Posts: 23
    you say no triplet has limited slip, how can that be?
  • tblazedtblazed Posts: 945
    Triplets have locking differentials, not limited slip.

    I would add that in some cases yes you do get almost twice the traction, for example on a wet street. With an open dif, it is easy to spin one wheel, the right rear, and go nowhere. With a limited slip, you will still spin the rt rear, but torque will transfer to the other side through the clutch pack in the dif, and if you spin the left wheel too, you will still have more forward drive traction from friction of two tires against the wet street. Happens easily with my S-10 that I put an Auburn Limited slip in back in '89.

    The Eaton G80 locker used in the Triplets adds a centrifugal mechanism to only engage the clutch pack when one wheel spins faster than the other and forward movement less than 20 mph. And they don’t simply "lock together", the two axles are then coupled together through a clutch pack. Otherwise if you spun a wheel taking off from a stop making a turn, there would be no “give”, there is with the clutches.

    This locker mechanism is desirable because No.1, the clutches are disengaged all the time unless wheel spin engages the mechanism. With a limited slip, the clutches are always engaged and work every time you go around a corner. That’s why you have to maintain a limited slip periodically, and why they do eventually wear out the clutches and get less effective. But a locking dif really doesn’t have a maintenance schedule except to check the oil level every 7500 mi .

    Reason No.2, with a limited slip on a wet street, making a corner, it is very easy to break both wheels loose equally because one breaks loose, transfers power/torque to the other wheel through the always engaged clutch pack, and in an instant both tires are spinning and you’ve just done a 360° in the intersection! I speak from experience. Above 20 mph a locker will act just like an open dif and you can’t break both rear tires loose under power on a slick spot.
  • blink3blink3 Posts: 74
    I am not getting it. I have read numerous publications stating Envoy's LIMITED SLIP DIFF option. Pull up the GM RPO for G80, it specifically states "positraction, limited slip" Where are you getting the info that it is a "locking diff"?? I am not saying you are wrong and please do not take it that way. I am just wondering where you are getting your info.
  • mookie14mookie14 Posts: 252
    01 hoe um tell me this; im going to buy the borla like today or tomorrow depending when you read this. If i do not put the dynamat in my tblazer or sound deadener materials will i wish i did. Or can i get by without it in the meantime. lastly will i be able tell a big difference from the stock to the borla thanks man.

    It refers to it as the "Eaton G80 locking rear differential." Eaton has to be considered the correct source.
    Also, from GMC, the option has always been "locking rear differential."

    Those RPO codes are different year to year. Do a query on GMC Envoy RPO G80.

    I'm sure there are articles out there that refer to it as a limited slip differential. Some people simply use the terms incorrectly, thinking a limited slip and a locker are the same thing. To the non car nut, they basically are the same.
  • n7donn7don Posts: 188
    "Where might I find a list of what all those codes mean???"

    This link is a gateway for several model years.
  • blink3blink3 Posts: 74
    Ok, cool. So it is like a hybrid of a true locking diff and the limited slip. So, could you guys look above and see where I wrote about that slight vibration, I think I titled it "anyone felt this". Is this common with this rear end or perhaps are the dogs worn and it is not engaging as it should. The more I think of it, it always happened when I was turning, low speed.
      Also, calling amsoil today to see if their new gear oil is compatible. I am assuming since there are still clutches in there that you would still need fluid compatible with limited slip?
    Thanks for all the great info!!!!!
  • tblazedtblazed Posts: 945
    To answer your first question, no, I have felt no vibration or anything unusual rounding corners with my locking dif. If you do might want to take it in and get it checked.

    As far as Amsoil, I did email them and they replied back their gear oil would work fine, then at the bottom of the response there was this disclaimer:
    "Every attempt has been made to ensure that the information provided in this e-mail correspondence is accurate and reliable. However, AMSOIL Inc. makes no warranty, guaranty or promise (express or implied) concerning the
    accuracy of our e-mail response as it is based solely on the information provided to us by the e-mail originator."

    Also emailed Royal Purple. Their response was:
     "Our Max Gear 75w90 meets and exceeds that GM spec.

    Patrick Burris
    Technical Advisor
    Royal Purple Ltd."

    And no disclaimers. My dif now has two quarts of fresh Royal Purple 75W-90 in it. This oil is readily available in a lot of auto supply stores too, unlike Amsoil.

    The "Genuine GM" gear oil is $20-30 a quart compared to less than $9 a qt for Royal Purple, and the RP already has the friction modifier additive for limited slip in it.
  • aldanaldan Posts: 19
    Yes TB's, Envoy's all have the option of the Limited Slip rear, but you are all wrong Eaton supplies only a small portion of this assembly, American Axle builds and assembles all the rear ends for our trucks, forgings/spider gears to the end brake rotor is all 100% American axle, except Timken Bearings.
  • tblazedtblazed Posts: 945
    "TB's, Envoy's all have the option of the Limited Slip rear"

    You might want to check your service manual. NO "limited slip" - only the Eaton locker is shown.
  • 01_hoe01_hoe Posts: 273
    Your tolerance for noise may be much different than mine. You may find you don't want or need any sound deadener. Some people like loud music, some don't. Where I noticed the noise problem was at 1500 to 2000 rpm in high gear. A lot of droning or resonance. The area around the rear wheels is one big echo chamber, and can readily be seen when the inside trim is removed. This area is where a lot of the noise comes from.

    I did not notice a big performance gain from the Borla. I do like the visual gain.

    If you go ahead with the Borla, make sure you keep your old system for a while to make sure you are satisfied with the Borla. That way you can reinstall the OEM and sell the Borla if it is not what you want. The GM OEM parts are expensive to replace when you have to buy them from GM.
  • funitsfunits Posts: 55
    I have a 2002 GMC Envoy, 4WD with the G80 differential. When new, it made noises starting up from a stop and turning left. After a couple of complaints to service, they replaced the rear-end gear oil (under warranty). That did the trick, no noise in 40,000+ miles.

    Replacement Tire Question: My original equipment Michelin Cross Terrain tires should be replaced before another Northeast winter. The Michelin tires have been great, but are expensive. I was wondering if anyone has any experience/comments on Pirelli Scorpion STR A tires? The Pirellis are less expensive than the Michelins, but seem to have good write-ups.
Sign In or Register to comment.