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Thread: Oil for rear axle?

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    Senior Member warwick-steve's Avatar
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    Oil for rear axle?

    Hi all
    Just wanted to check if Comma 80/90 GL4 oil is OK for the rear axle in a BT7?
    Thanks
    Steve

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    Darth Vader Michael Oritt's Avatar
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    Re: Oil for rear axle?

    Steve--

    I do not pretend to understand the technical difference between GL4 and GL5 oils but do know that differentials place tremendous loads upon lubricants which is why you will see words such as "Extreme Pressure" etc. in differential oil names, etc. I'm sure someone else will chime in but since there is no yellow metal in your diff there is no reason NOT to use a GL5 oil which is designed for differentials, not transmissions. The 80/90 refers to viscosity, not the oil molecules' resistance to shearing forces, and that--"High Pressure" or "Extreme Pressure" tolerance is what you are after.

    Best--Michael Oritt
    1954 Austin-Healey 100 Lemans
    1958 Elva Courier (FOR SALE)
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

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    Senior Member warwick-steve's Avatar
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    Re: Oil for rear axle?

    Hi Michael
    Thanks for replying. I should have stated EP80-90 GL4.
    Steve

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    Darth Vader Michael Oritt's Avatar
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    Re: Oil for rear axle?

    Steve--

    Go here: http://www.widman.biz/uploads/Transaxle_oil.pdf

    and I believe you'll see why you use a GL5 in the diff and not a GL4--and visa versa.

    Best--Michael Oritt
    1954 Austin-Healey 100 Lemans
    1958 Elva Courier (FOR SALE)
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

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