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Thread: Rear Differential Fluid

  1. #1
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    Rear Differential Fluid

    What gear oil do you run in your rear differential? I know the owners manual says 75w140, but I think now we're supposed to run 80w90.

    Looking on Rock Auto, the Motorcraft 80w90 shows Premium Rear Axle Lubricant. The Motorcraft 75W140 shows Synthetic.

    I think we supposed to use full Synthetic?

    Rock Auto has a Mobil 1 75w90 that is Synthetic.

  2. #2
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    you have that backwards, the 80W90 call was superseded by 75W140

    run a 75w140 synthetic that has limited slip additives (most should)


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    2004 Mercury Marauder - Eaton M112, Billetflow 3.4, Accufab SBTB + Plenum, T-56 Magnum, 4.10s, Stainless Works LTs, 2.5" Exhaust, Borla Stingers, Ridetech Coilovers + Adj rear shocks, FX-R projectors, Wilwood 13" BNSL6 + FNSL4 BBKs, S55 Gauge Cluster
    440rwhp & 406rwtq Tuned by Adam @ Revolution Automotive
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    (Sold) 2003 Mercury Marauder - Stainless Works LT's, Stainless Works 2.5" Catback, JLT Intake, Mo's Xcal4 Tune
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  3. #3
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    Ahhh. Thanks for the help.

  4. #4
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    Holy crap it's expensive. Rock Auto has it at $22.89 per quart, whereas 80W90 is only $7.59 per quart.

  5. #5
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    Use 75W140 synthetic, Using synthetic negates the need for friction modifier.
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
    General James Mattis




  6. #6
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    Quote Originally Posted by crouse View Post
    Holy crap it's expensive. Rock Auto has it at $22.89 per quart, whereas 80W90 is only $7.59 per quart.

    Go to Walmart, they have tons of 75w140 in stock. No reason to mail order that unless you're going to use something more boutique like Amsoil. Most are around $15 at Walmart.


    2016 Ford Mustang GT PP - Lund nGauge, BMR vertical links, MGW Shifter, BMR CB005

    2004 Mercury Marauder - Eaton M112, Billetflow 3.4, Accufab SBTB + Plenum, T-56 Magnum, 4.10s, Stainless Works LTs, 2.5" Exhaust, Borla Stingers, Ridetech Coilovers + Adj rear shocks, FX-R projectors, Wilwood 13" BNSL6 + FNSL4 BBKs, S55 Gauge Cluster
    440rwhp & 406rwtq Tuned by Adam @ Revolution Automotive
    2063/3214

    (Sold) 2003 Mercury Marauder - Stainless Works LT's, Stainless Works 2.5" Catback, JLT Intake, Mo's Xcal4 Tune
    5377/7838

    2000 BMW M5 - Evolve Intake, Evolve Alpha-N tune, Stoptech ST-40 BBK, UUC SSK, Dinan front STB, Dinan RSB

    1996 Ford Bronco - 4" lift, 35" BFG A/T's, Punisher Valve Body, MH1 Projectors

  7. #7
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    How much fluid do we need to change the gear oil?


    Sent from my iPhone using Tapatalk

  8. #8
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    Whats the reason for the switch to 75w140? I think thats what the police vics use.
    2004 Mercury Marauder, Black
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  9. #9
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    Quote Originally Posted by BLACKMARAUDER04 View Post
    How much fluid do we need to change the gear oil?


    Sent from my iPhone using Tapatalk

    2.5 quarts, although 2 quarts is usually enough if you're not pulling the axles and getting ALL of the fluid out

    Quote Originally Posted by JVD View Post
    Whats the reason for the switch to 75w140? I think thats what the police vics use.
    don't know, ask Ford


    2016 Ford Mustang GT PP - Lund nGauge, BMR vertical links, MGW Shifter, BMR CB005

    2004 Mercury Marauder - Eaton M112, Billetflow 3.4, Accufab SBTB + Plenum, T-56 Magnum, 4.10s, Stainless Works LTs, 2.5" Exhaust, Borla Stingers, Ridetech Coilovers + Adj rear shocks, FX-R projectors, Wilwood 13" BNSL6 + FNSL4 BBKs, S55 Gauge Cluster
    440rwhp & 406rwtq Tuned by Adam @ Revolution Automotive
    2063/3214

    (Sold) 2003 Mercury Marauder - Stainless Works LT's, Stainless Works 2.5" Catback, JLT Intake, Mo's Xcal4 Tune
    5377/7838

    2000 BMW M5 - Evolve Intake, Evolve Alpha-N tune, Stoptech ST-40 BBK, UUC SSK, Dinan front STB, Dinan RSB

    1996 Ford Bronco - 4" lift, 35" BFG A/T's, Punisher Valve Body, MH1 Projectors

  10. #10
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    So had the differential serviced.
    Replaced the girdle with a Finned one from Amazon’s brand A+. Very reasonably priced. It doesn’t include screws. The seal is RTV. No gasket needed. You just need the RTV to dry enough to finish sealing. The repair person got the screws from O’Reily’s.

    Now for some reason. the alignment is way off. The steering wheel is facing 8 o’clock. It’s on the rack being fixed as I type this.


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  11. #11
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    Was the steering wheel straight when you drove it to the shop?
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  12. #12
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    Quote Originally Posted by BLACKMARAUDER04 View Post
    So had the differential serviced.
    Replaced the girdle with a Finned one from Amazon’s brand A+. Very reasonably priced. It doesn’t include screws. The seal is RTV. No gasket needed. You just need the RTV to dry enough to finish sealing. The repair person got the screws from O’Reily’s.

    Now for some reason. the alignment is way off. The steering wheel is facing 8 o’clock. It’s on the rack being fixed as I type this.


    Sent from my iPhone using Tapatalk
    Changing the fluid and replacing the differential cover has NOTHING to do with the front end.
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
    General James Mattis




  13. #13
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    Obviously, the alignment has nothing to do with the differential. That’s why it was mysterious. The steering wheel was not straight. I had to drive with it pointing left. It’s all fixed now.
    They also fixed a flat tire( for free)
    Off one of the other Marauders


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