Can't find synthetic SAE 90 gear oil

Discussion in '100-Series Cruisers' started by Timber, Jul 22, 2004.

  1. Timber

    Timber

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    I have a 98 LC (4.7 V8) with about 77 k miles on it. Based on a lot of advice found on IH8MUD, I decided to change out my transfer case oil and all differential oil to synthetics. I can find 75W90 all day for the transfer case. But no one (locally, at least) has a synthetic GL-5 SAE 90 gear oil.
    I'm hesitant to change to synthetics if it's going to be this much trouble -- since I'd really like to be able to pick up oils locally rather than placing an Internet order every time a fluid needs topping off or changing.
    I'm hoping someone out there can suggest a readily available substitution.
    Thanks for any help.
    Best,
    Mike
     
  2. cary

    cary SILVER Star

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    Don't worry about the SAE spec. It is as worthless as the ink used to print it. Just make sure that the oil is rated GL-5. Redline 75w-90 Gear oil, Mobil 1 Gear Lube, Amsoil Gear oil, and many others all meet this spec.
     
  3. Cruiser4UGA

    Cruiser4UGA

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    Have you tried 80w-90, the manual says to use 75-90 in the transfer case and 90wt or 80w-90 in the two diffs. The difference being temperature range 90 for above -18 and 90w-90 for below. Sae 90 is impossible to find regardless of synthetic or dino, I run 80w-90 in GA where it never gets near -18 and I do great.
     
  4. calamaridog

    calamaridog

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    Ok so all I can find at the local autoparts stores is 75w-90 Mobil 1, which I have used in the past (and which I happen to have about 30 quarts of). So how many of you are running 75w-90 in the Diffs? The transfer case only takes >2quarts of 75w-90, so at that rate, I have a lifetime supply of Mobil 1 for the t-case:) But I'd like to use it in the Diffs as well, so who else does this?
     
  5. NMuzj100

    NMuzj100

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    Most owners on this board use the 75-90w in the differentials with no bad reports. Amsoil has a 80-90w gearlube and I am running it but if I had 30 Quarts of Mobile1 already I would use that.
     
  6. calamaridog

    calamaridog

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    Thanks, that is how I'm leaning since I ran it in the diffs on the Taco. Just wanted some reassurance...

    Hey, it was a good price and I couldn't pass it up:)
     
  7. hank14

    hank14 SILVER Star

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    I've had 75W-90 Amsoil in both diffs and the transfer case in mine for 1.5 years. I change it out once a year (about 12,000 miles). This is what was recommended by the Amsoil tech guys.
     
    Last edited: Jan 31, 2005
  8. Pskhaat

    Pskhaat

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    You will be totally fine with 75-90 in all three. An SAE viscosity difference of 5 is quite close. Our engines call for 5-30 but we all run different weights for the most part.
     
  9. Augie

    Augie

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    I use redline Heavy shock proof gear oil for the differential. It was rated at 75W250. Thinner than SAE 75 but provide protection like SAE 250 grade.
     
  10. marques

    marques

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    I use Redline synthetic 75W90NS in all differentials and transfer case. I have used it for >35k miles with no problems what so ever. This fluid is good for 5 years or 50k miles of normal use easily, unless you do a lot of trailer towing or serious off road use (then you might want to change it every year or two). This is very high quality fluid and is worth the price of ~$8/qt.

    The Redline shockproof oils only last a year or so and then their special additive is all used up and it's like a thinner fluid. They work great, but you do have to change them more often.

    -Luis Marques
     
  11. NMuzj100

    NMuzj100

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    What does "Shockproof" mean on the Redline oil? I think that the GL-5 rating is the key rating in a gearlube. But 250 weight is quite a bit different than 90 weight. I think most gear lube will last 50,000 miles because there is not that much heat invoved in the differential. Gear Lube is changed mostly to eliminate contamination in the lube from water so length of service is probably more important than miles driven.
     

  12. hank14

    hank14 SILVER Star

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    And I change mine to get some idea what's going on in there. I think those magnetic drain plugs say a lot (same with the tranny).
     
  13. jp213a

    jp213a

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    Quote: This is very high quality fluid and is worth the price of ~$8/qt.

    What makes it "high quality"....the $8/quart price?
     
  14. marques

    marques

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    Basically, it's made of a very stable synthetic base that will resist breakdown due to shear and heat. Obviously it also has all the required GL5 aditives. So it won't break down and thin or thicken ad you rack up the miles. If your differential gets hot, it will protect your gears a lot beter than any off the shelf mineral base gear lube. Many race cars use nothing but redline in their transmissions and differentials because it's one of very few fluids that will stand up to that kind of abuse. It's a little overkill for a grocery getter, but very good insurance for your gears none the less.

    A small side benefit is slightly better MPG and power to the wheels compared to a conventional fluid.

    -Luis Marques
     
  15. NMuzj100

    NMuzj100

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    On the Redline Website they don't state whether their ShockProof oils meet GL-5. They do show that their 75W-90 Synthetic gear Lube exeeds GL-5 standards.
     
  16. cary

    cary SILVER Star

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    The shockproof oils are designed for gearboxes that use straight cut gears and are shifted under load with no clutch. Basically, custom race car boxes.

    For the LC you should be using the Redline 75w-90 Gear oil in the diffs and T-case if you are using redline.
     
  17. Jim_Chow

    Jim_Chow

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    To renew an old thread, should one use 75w90 gear oil w/ limited slip additives or w/o the additives in the t-case? I noticed that Redline sells both (75w90 and 75w90 NS). Doesn't the 100's t-case have limited slip type clutches in there?

    Anyone try both M1 gear oil and compare it to Redline after use? I've only used Redline (MT-90 in my mini...keeps the stick a lot cooler for desert driving than Mr. T's MTF, so I know it's doing something. The MT90 still looked great [clear & as thick as new] after 30K mi of driving in So. AZ (compared to Mr T's, that looked hazy & thin after only 21K mi of So. CA driving), so this gives me high confidence in Redline products).
     
  18. hkeller

    hkeller

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    This will probably bring cries of horor and attack against me, but I don't think synthectics have any place in differentials. In any internal combustion engine, I run nothing but sythetics. However, my diffs are all dyno oil.

    Here is why. Dyno oil is made up of small chains of oil molecules. Synthic is made up of small groups or balls of oil molecules. (Note, this is not scientific terminology!) The synthetic balls slip very quicky out of the way when the gears come toghther, the dyno chains take a little longer to get out of the way. As such, the dyno oil provides a better "cushion."

    A guy I know owns a company that has about a dozen medium duty trucks. When he switched the differentials to all synthic, he thereafter replaced two rear ends. He never had that problem with dyno.

    I am not sure how this all comes into play in chain driven transfer cases. It would be worth some analysis.

    I kinda hope someone out there will tell me I am wrong, as I am a big fan of synthetics.
     
  19. Tinkerer

    Tinkerer

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    Dunno about the specific test used to rate gear oil viscosity for low vs. high temp (the 75"W" number vs. the second number 90 in the SAE "75W-90" rating).

    But plain synthetics generally have significantly "better" ("thinner" or less viscous) COLD flow properties than plain dino without viscosity index modifers, all else being equal. So it may be that, unlike dino, synthetics are simply not available in a single SAE viscosity rating for entire SAE rating temperature range, per the standard rating & test. The synthetic gear oil rated at SAE 90 at high temp will be less viscous than a standard SAE 90 dino gear oil, at low temp, hence the "75W" for the 75W-90 synthetic, vs. the plain single number "90" for the plain dino.

    FWIW, I run Mobil 1 75W-90 in the center & front diffs, but use dino LSD gear oil in the rear, since the LSD change interval will generally be shorter than non-LSD: I figure that the more-frequent changes at the rear will tend to minimize potential benefits of synthetic vs. dino, plus carry a cost penalty. Also, synthetics have been known to cause problems with LSD clutches, so I'm playing it safe by using dino LSD stuff. (I believe the owners manual also agrees with the change interval difference, but can't remember the exact quote.)
     
  20. calamaridog

    calamaridog

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    I use synthetic in the engine and in the differentials and transfercase. I do not use synthetic in manual or automatic transmissions, or power steering.

    This is based upon recommendations from my mechanic and my cousin who has been a mechanic for a long time. This is also based upon personal experience and good luck with my differentials and transfercase running synthetics.

    I really don't know the answer so I'm not going to say you are "wrong". What I do know, is that the 5spd manual transmission in my Tacoma DID NOT like synthetic and I quickly switched back.
     

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