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  1. #1
    GW74
    Guest

    Default Differential fluid change

    I would like to change the fluid in the differential of my 74. I plan on sucking it out with a vac pump. I have two quarts of GM differential gear fluid and one 4 oz. bottle of GM posi additive. Doe anyone know what the capacity of the housing is? Any tips from anyone who has already done this.
    Thanks

  2. #2
    wicky88s1975's Avatar
    Join Date
    May 2002
    Location
    Simi Valley, CA USA
    Posts
    133
    Corvette(s)
    1975 Red on RED Coupe

    Default

    Happened to come across it in the 1975 assembly manual. 4.0 pints is what that says. let me know what kind of pump you used. I'm in the process of a full suspension rebuild and I might as well do the same since all the parts are out.

  3. #3
    jet4rs
    Guest

    Default

    I drained mine with a hand pump. It worked. Just a tad slow but the pump was cheep and I was able to throw it away when I was done.
    Getting the fluid back in was a different story. I couldn't get the oil bottle up high enough to gravity fill it so with a piece of clear plastic tubing a snug fit over the oil tip I was able to squeeze it in. I had a mess when I was done and lost a couple of ozs. But the job was done.

    Good Luck
    Bob w/jet4rs

  4. #4
    hotrodd
    Guest

    Default

    I put the fluid back in by using tubing with a funnel in the end and held it higher than the car,garden hose stuff would work if you can get the hose in the diff. Hope that help's.

  5. #5
    DDLS3's Avatar
    Join Date
    Nov 2000
    Location
    Scottsville, Kentucky
    Posts
    1,499
    Corvette(s)
    08 Jetstream Blue Z51 coupe

    Default

    GW74,

    Your quart bottle should have a tapered top that will insert into the opening of the gear case, then squeeze the bottle. Put the tapered top onto your bottle of additive and put that in first, followed by the gear lube. If this dosent work for you get a small piece of tubing from the local parts store and squeeze the fluids through it. It likely won't take all of the second quart of lube.
    Dale

  6. #6
    Member
    Join Date
    May 2002
    Location
    Easton, PA USA
    Posts
    95
    Corvette(s)
    1982 Collectors Edition

    Default

    I did it with a hand pump, tedious but it worked. I would recommend putting bottle of lube in and then the additive. Then top off with the lube. That way you get al posi additive in there. Don't forget to do SLOW forward and backward figure "8's" in a parking lot to lube the clutches

  7. #7
    Dave L.
    Guest

    Default

    Removing the fluid is much easier if you drive the car and get the gear oil warm. Sucks out much easier!! I always use the vacum pump to install the oil also.

    Dave

  8. #8
    Member ChuckG's Avatar
    Join Date
    Nov 2001
    Location
    Florida
    Posts
    603
    Corvette(s)
    63FI, 69BB

    Default

    You can buy a cheap "slurp" gun at PEP Boys, etc. Looks like a huge medical syringe with a 12 to 14 inch vinyl end. Put the end in the diff and suck it out. To replace the fluid, do the opposite. Load the "slurp gun" and push the fluid back in till it drips out of the hole. MUCH neater....minimal mess. That gear oil stinks to high heaven IMHO, it's tough if not impossible to use the gear oil bottle with it's little end to put fluid in. Not much room to get the bottle high enough, especially working around the exhaust system/ rear spring/ spare tire carrier. Chuck
    1963 Corvette Conv., Red/Black, 327-360HP FI, 4 SPD, NCRS Top Flight
    1969 Corvette Conv., Orange/Black, 427-400HP, Automatic, NCRS Top Flight

    1956 Chevy 150 2 door sedan. HOT ROD. 355CI, 4 Speed, Vintage Air, NEAT cruiser

  9. #9
    Member
    Join Date
    May 2002
    Location
    Charlotte, NC USA
    Posts
    39
    Corvette(s)
    96 LT1 Competion Yellow

    Default Gear Oil Capacity

    Two 23-oz. bottles of GM Rear Axle Lubricant and one 4-oz. bottle of GM Positraction additive filled her up to the bottom of the hole.

    GM dealer gave me a cap with a short piece of plastic hose that attachs to the Axle lub bottles. Went in with no problem. Just get the bottle up higher than the fill hole.

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