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Thread: Mixing MT-90 with Hypoid Gear Oil?

  1. #1
    Luke Skywalker mrv8q's Avatar
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    Mixing MT-90 with Hypoid Gear Oil?

    Should I do this? 1 quart of the Red Line didnít quite fill the TR3 gearbox, and I have plenty of the StaLube 85W 90 in the garage. Canít get the MT-90 locally, otherwise Iíd just go get it.

    Interwebs are mum on this subject, though I think I know the correct answer...
    Best, Kevin Browne
    '59 TR3A #TS58370L
    Look for The Curse of Oak Island on The History Channel

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    Yoda dklawson's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    The rule of thumb and best practice is not to mix oil types. If your gearbox is "close" to being full, drive the car gently and limited distances until you get more of the MT-90.
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

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    Yoda poolboy's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Says here 'compatible with petroleum and other synthetics'
    https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil
    DRIVE 'EM IF YOU GOT 'EM

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    Great Pumpkin TR3driver's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Compatible meaning nothing really bad happens. But you also lose at least some of the advantage of the better oil.

    Kind of like mixing Thunderbird in your single malt. Won't kill you, but might not taste very good either

    I'm with Doug, order another bottle and drive with it a bit low until it gets there. But IMO there is no need to baby it as long as its just an ounce or two low. The "full" level includes a reasonable margin for leakage between refills.

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    Moderator Andrew Mace's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    One might be surprised as to how low the oil level can get before the gearbox starts to remind you it's thirsty!
    -- Andrew (Andy) Mace, VTR's Triumph 10/Herald/Sports 6 vehicle consultant and keeper of the North American Triumph Sports 6 and Herald Database

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    Luke Skywalker mrv8q's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Thanks, all. Thanks to our friends/ overlords at Amazon, they promise I’ll have another bottle today. I wasn’t keen on mixiy, so this worked out. Changing the gearbox oil was a “while I was in the neighborhood... “

    I did a quick rebuild of the clutch master cylinder and am going to replace the hydraulic hose, all to cure an occasional balky-shifting gearbox. Fingers crossed...
    Best, Kevin Browne
    '59 TR3A #TS58370L
    Look for The Curse of Oak Island on The History Channel

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    Yoda dklawson's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Quote Originally Posted by mrv8q View Post
    Changing the gearbox oil was a “while I was in the neighborhood... “
    We no longer have our Spitfire but one of the modifications I made to it was the addition of an access hole on the side of the tunnel cover. I fit a large rubber grommet type plug into the hole. Whenever I wanted to top up the gearbox oil I'd peel up the carpet, pop out the rubber plug, then remove the fill plug and fill away.
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

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    Obi Wan
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Do they still make T-Bird Randall, maybe in Cal plus I thought the gearboxes drank 30 W non-detergent

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    Luke Skywalker mrv8q's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    I smiled at the Thunderbird reference as well. I actually used to sell it in a previous lifetime. 1.59 back in the day?

    My gearbox takes 6 pumps over the original quart to fill... go figure. At least I know it’s full.
    I plan to fill and bleed the new clutch master cylinder on the weekend, drop it from the jacks, and see how nicely my new refurbished clutch system works. Fingers crossed...

    Definitely a good idea about an access hole, Doug. If I have to go back in, it’s on the list.
    Best, Kevin Browne
    '59 TR3A #TS58370L
    Look for The Curse of Oak Island on The History Channel

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    Great Pumpkin TR3driver's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Quote Originally Posted by sp53 View Post
    Do they still make T-Bird Randall, maybe in Cal plus I thought the gearboxes drank 30 W non-detergent
    I haven't a clue about the Tbird; but if Gallo still makes it, I'll bet they sell it nationwide. Don't recall ever seeing it on a shelf here in CA; but then I don't spend a lot of time in the kind of places that usually sell it.

    Triumph did originally recommend motor oil for the gearbox (although there is an early TSB suggesting that gear oil is OK too, without overdrive). But then, about the time the TR3A was (unofficially) introduced, they switched to specifying GL4. Ken Gillanders once wrote that an ex-factory engineer told him that they were having too many countershaft failures, and the GL-4 provided better protection. S-T and later BL continued to specify GL4 through the end of TR6 production, so evidently they felt it worked.



    Personally, I really like the MT-90. Doesn't change OD performance much, but makes a noticeable improvement in the main gearbox IMO; in the form of easier, more positive shifts. My synchros are getting somewhat worn now, but with almost 200,000 miles since the main box was overhauled (1997 IIRC), I consider that pretty good service.
    Randall
    56 TR3 TS13571L daily driver
    71 Stag LE1473L waiting engine rebuild
    71 Stag LE2013LBW waiting gearbox rebuild

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    Jedi Hopeful
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    oh they still make it...


  12. #12
    Obi Wan
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Ok, what weight oil would you guess GL4 is, 75? Or does GL4 calibrate that way.

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    Great Pumpkin TR3driver's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    GL4 is a performance standard for gear oil; so it can be any of the gear oil weights. 90 is probably most common, ISTR MT-90 is actually rated 75W90 but Redline also offers MTL which is 75W80. I've also got a jug of 140 weight GL4 in the garage.
    Randall
    56 TR3 TS13571L daily driver
    71 Stag LE1473L waiting engine rebuild
    71 Stag LE2013LBW waiting gearbox rebuild

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    Luke Skywalker mrv8q's Avatar
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    Re: Mixing MT-90 with Hypoid Gear Oil?

    Just to button up this post... bled the clutch master cylinder, dropped the car off the jacks, and took it for a spin around the block. Car seemingly shifts fine, can’t tell any difference yet.

    Going for a 50 mile round trip tomorrow morning, so that will be the real test. WooHoo, glad to see the car at its appropriate height in the garage.
    Best, Kevin Browne
    '59 TR3A #TS58370L
    Look for The Curse of Oak Island on The History Channel

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