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Thread: 4WD Front Diff

  1. #1
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default 4WD Front Diff

    Any diff experts in here?

    I've had a 1999 Mazda Bravo for about 5 years. Its been used as a low mile paddock car. Its had what I thought was a bad front CV shaft since we got it, but the time has come to fix it.
    While pulling it apart its doing some strange things that I just cant get my head around. (Also explained a few things when I found the drivers side hub wasn't disengaging)

    With the passenger side in the air and the drivers side on the ground you could rotate the wheel forward but not backwards. So its an open diff with a strange issue(unless a CV can get that bad?)
    Lift the drivers side off the ground and turn the drivers wheel, the passenger side goes in the same direction i.e. its a locked diff.
    How is that possible?

    Drop the diff oil, looks good. Fished around with a magnetic screwdriver, no chunks.

    Only other strange thing is there is 45 degrees backlash on the front pinon! (now some of that comes from the CV shaft, hub etc. But I didn't get a number)
    Now I know that's not how backlash is normally measured so I checked the rear diff the same way, it has 6 degrees.

    Knackered you say? Well I have access to a 2002 Ford Courier(pretty much the same pig with different lipstick) so I checked that.
    34 degrees backlash on the front(-6 degrees of back lash in the CV shaft, hub etc)
    7 degrees on the back.

    So are both diffs shot or is that just how they roll?

  2. #2
    Join Date
    May 2023
    Location
    Canberra, Nimmitabel
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    72
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    144

    Default

    I'm curious about your problem. It seems odd. Diffs usually cause the opposite wheel to rotate in the opposite direction when you rotate the other, if both wheels are off the ground. I wonder that you might get better advice from a Mazda forum.

  3. #3
    Join Date
    Jul 2010
    Location
    Melbourne
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    Default

    Quote Originally Posted by ErrolFlynn View Post
    Diffs usually cause the opposite wheel to rotate in the opposite direction when you rotate the other, if both wheels are off the ground.
    Yes with an open diff that's correct. Which is what these 4WDs come with standard in the front. LSD rear. I'm not even sure the tailshaft was spinning when I had the passenger side up! I just assumed it as because "open diff"
    With LSD or locked diffs both wheels spin the same way.
    Not sure what lockers do.


    I might try somewhere else if I have no luck here, but its not often there's a subject someone here doesn't know something about. I have another post coming about pretensioned concrete lol

  4. #4
    Join Date
    Jul 2003
    Location
    Sydney
    Posts
    493

    Default

    Most likely an auto locking hub.
    You can get a new old center from wreckers. They are not very expensive. New CV a must.
    Or pull out and take to a diff guru. That would be my choice.
    Good luck
    Civilized man is the only animal clever enough to manufacture its own food,
    and the only animal stupid enough to eat it.
    Barry Groves

  5. #5
    Join Date
    Jul 2010
    Location
    Melbourne
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    9,088

    Default

    Quote Originally Posted by Marc View Post
    Most likely an auto locking hub.
    Sadly that cant be it as they are both have manual hubs.

    Quote Originally Posted by Marc View Post
    You can get a new old center from wreckers. They are not very expensive. New CV a must.
    Or pull out and take to a diff guru. That would be my choice.
    Good luck
    A quick look puts them at about $500, but of course they maybe exactly the same???
    Yes I have to shafts here. Waiting on some bushings. Just trying to get my head around if I need to pull the diff or not*.

    *not that I can pull the diff ATM as I need to use the vehicle, but I can get by without 4WD in the short term so now I have the freewheel hub fixed I can put it back together as is.

  6. #6
    Join Date
    Jul 2010
    Location
    Melbourne
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    Just to give a result. It turns out its not the CV(although it was stuffed)
    It would appear my $2k 4WD has a $500 lunchbox locker in it and while I haven't jack up my other 4WD I assume its the same.
    Well that would at least explain the noise(one isn't working 100% for some reason) and the backlash. They aren't banjo diffs so for the minute I'm not pulling one to see.
    https://www.youtube.com/watch?v=hkTHnsZmTQo

    Turns out one of the hubs wasn't disengaging which explains some of the funny noises.

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