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  • Transmission / Overdrive: Transmission service

    Transmission is 3 speed overdrive on a 3/4 ton truck. Thinking of draining and flushing with diesel the replacing fluid with 90W gear oil. Thoughts and or advice?

  • #2
    Have the same trans in my '63 Champ. Shop Manual says "Drain-Flush-Fill every 10,000 miles" but neglects saying what to use to flush. I recently drained and refilled (skipped the flush). Used 90W Mineral Gear Oil API GL-1. NAPA 65-201.

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    • #3
      Use 90W mineral oil. Be sure to drain and fill both plugs (trans & OD). NAPA part # 65-201.
      BOB GOT HERE BEFORE ME.

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      • #4
        That is Correct info to remember, do NOT use the common GL-4, 5 or combination of GL Ratings Gear Oil, they all contain "EP" Extreme Pressure additives only for Hypoid Gears in Differentials.

        Diesel or Kerosene should not hurt as long as you get it about 95% or more Dried out.
        Unless it is severely "gunked up", it should not be necessary.
        Last edited by StudeRich; 03-30-2020, 01:03 PM.
        StudeRich
        Second Generation Stude Driver,
        Proud '54 Starliner Owner

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        • #5
          Thanks very much to all

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          • #6
            I have been using Redline MT-90 since Ted Harbit mentioned it here maybe 15 years ago. It shifts real smooth, even when cold. It is GL-1, Gl-3 and Gl-4 rated, and will not harm the bronze synchronizer rings in our Studebaker standard shift transmissions. After trying Redline, I will never go back to mineral oil. Click image for larger version

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            • #7

              So, for rear-end/differentials, use GL-4, 5 Gear Oil? Also, Redline MT-90 does not contain Extreme Pressure additives?

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              • #8
                Originally posted by JohnAustin View Post
                So, for rear-end/differentials, use GL-4, 5 Gear Oil? Also, Redline MT-90 does not contain Extreme Pressure additives?
                Here is a link to Red Line's site. It says their MT-90 is safe for brass synchronizers, since there's no sulphur in it, as found in most GL-5 oils. I have found it to be everything they say it is re: smoother shifts, etc..

                For rear ends, use GL-5, which has extreme pressure additives. The MT-90 is not rated GL-5, which means it does not have EP additives.Red Line Synthetic Oil. MT-90 75W90 GL-4 Gear Oilwww.redlineoil.com › Gear Oil › Gear Oil for Manual Transmissions
                Last edited by JoeHall; 04-14-2020, 10:04 PM.

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                • #9
                  Thanks again, Will order a gallon today

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                  • #10
                    The Red Line does make a difference in shifting so thanks again for the recommedation

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                    • #11
                      What lubricant would you recommend for the steering gear box?

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                      • #12
                        since your recent problems with the transmission, I would suggest taking a magnet and a sieve to that old oil and check for large chunks just to be safe.

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                        • #13
                          Good advice as has also been a couple of years since I Changed it. Still can’t figure out what happened with this unless the gear shift levers at the shift box got out of sync or there is a solenoid problem. Your thoughts?

                          I have MT-90 in the steering gear box. Does that oil seem heavy enough?

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                          • #14
                            The Original Kendal Steering Gear Box Lube for Ross Boxes was Semi-Fluid Grease, not Oil, so a better product would be the John Deere Corn Head Grease or Similar, as sold at Studebaker Vendors.

                            When buying Standard Transmission Oil, the thing to remember is the API GL Rating, if getting Dino Oil, it is GL-1, and Never use any combination of Ratings like 3, 4 & 5.
                            Last edited by StudeRich; 06-17-2021, 05:19 PM.
                            StudeRich
                            Second Generation Stude Driver,
                            Proud '54 Starliner Owner

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                            • #15
                              Originally posted by JohnAustin View Post
                              What lubricant would you recommend for the steering gear box?
                              john deere corn head grease.

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