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Thread: Rear end noise

  1. #1
    bluegrill is offline Cadillac Owners Member
    Automobile(s): 1975 Coupe DeVille
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    Rear end noise

    I have a noise coming from the rear of my '75 Deville. It is a whine like gear whine. Sounds like the sound you get from a manual tranny in reverse. It starts out low in pitch and increases to a high pitch whine with speed. Definitely related only to vehicle speed. Above 55-60 mph it is barely aubile. So, I'm thinking differential. I opened the diff fill plug and stuck my pinky in just to make sure I had lube in there. The color and consistency of the lube in there looks an awful lot like Auto trans fluid. I've only had this car a few months. If someone had put ATF in the differential would it cause a whine like that? Would any damage likely have ocuured? Any opinions would be apreciated.


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  3. #2
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Rear end noise

    Some rear axles use ATF. Maybe someone thought it would make the car get 30 MPG. If that's what you have in there change it A.S.A.P.

  4. #3
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Rear end noise

    ATF would not be good in there. I have never heard of anybody dumb enough to do this so I hope that's not the case. Gear oil is usually very thick and smells bad. This is why I always change fluids when I get a vehicle, just so I know what is in there.

  5. #4
    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: Rear end noise

    ATF is nowhere near the viscosity needed for a rear. It should be 80W90 gear oil. Much thicker.

  6. #5
    bluegrill is offline Cadillac Owners Member
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    Re: Rear end noise

    O.K. great. Thanks for the replies. It can't hurt to change it even if I'm wrong. Any idea how much gear oil it takes to fill it up? I think I read some where 4 1/2 pints. Does that sound right?

  7. #6
    SafariOne is offline Cadillac Owners Fanatic
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    Re: Rear end noise

    If you do have a rear problem it will most likely be the carrier bearing with a noise like that. Try the fluid first and if you still have the noise you can always recoupe the oil.

  8. #7
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Rear end noise

    That red fluid could have been an industrial gear lube. In industrial applications where transfer drive units are used, they get their oil from specialty oil producers. They produce a wide selection of lubricants for various applications, from transfer units to bearing lubes, also greases for various applications also. Most of these lubes have a red dye added to identify them. Someone could have substituted one of these gear lubes for rear gear lube and it is most likely the wrong viscosity for the application. Save a dollar, pay more later.

  9. #8
    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: Rear end noise

    You fill it until it comes out the fill hole.


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