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    Diff Cover Leaks, Breather Question

    Ok, I've reached the end of my rope, so I'm posting a thread.

    I just swapped a medium case LSD in to my 318is.

    The speed sensor, fill plug, and drain plug all keep leaking. The axle seals and pinion seal don't seem to be leaking.

    I ordered a new o-ring for the speed sensor, and new crush washers for the plugs, and installed it all tonight. I can't put a torque wrench on the plugs, but I'm tightening the hell out of them, so I feel like they should be creating a fine seal. (I used the wrench on the end of a wrench trick to get the drain plug as tight as I could without feeling like I was going to damage the aluminum threads.)

    I took it out for a test drive on the highway, and I'm still leaking oil from all three.


    I've done searches, and I can't find much information about the breather on these diffs. When I got the diff shipped to me, it had a black rubber cap on the breather. Should that be on there in the car, or was it just put on for shipping? Should the breather be left exposed? I know the point of a breather is to let air in and out as things heat and cool, but I figured the rubber cap was to keep dirt and debris out while letting the air vent on the sides.
    91 318is Members' Rides Thread

    #2
    Oh yeah, when it was leaking before I got the new seal and washers, I was losing enough oil that the back of the car had splatter on it.
    91 318is Members' Rides Thread

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      #3
      Rubber cover does NOT belong there. Did you replace the diff gasket with a new one? If you did, did you use gasket maker on it? What we have seen in the past is when diff gasket leaks, it APPEARS that leaks are coming from different places. New gasket is about $3 so it cant hurt to replace it if you did not do it yet. Also, make sure all your cover bolts are tight.
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        #4
        I haven't touched the diff cover. The diff is super clean, so I can see the oil visibly coming from the fill/drain plugs and speed sensor. I don't think there's any leaking around the cover gasket, at all. I'm using royal purple, so it's even color coded for me.

        I'll pull that rubber cover off the breather and see if that fixes things. That's the info I was looking for. Thanks! Though, I'd be surprised that an old rubber cover can hold more pressure than torqued down aluminum crush washers... so I'm not sold that it will solve the problem.
        91 318is Members' Rides Thread

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          #5
          Well, I slid under the car and pulled the rubber cap off the breather. The diff is still a little warm from my drive but it must be cooling down, because I could hear a rush of air whistle in when I slid the cap off. Hopefully that was causing my problems!

          Here's a picture of the cap next to the breather on my old diff, for context.

          91 318is Members' Rides Thread

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            #6
            I drove it a bit yesterday with the breather uncovered, and I've still got a few drips coming off of the drain plug. The drain plug is torqued as tight as I can get it with a 3/4" drive wrench.

            I guess the next step is to do a new cover gasket just to rule that out, but it REALLY looks like it's coming from around the drain plug. While it's off I can inspect it for cracks/damage.

            Any other ideas?
            91 318is Members' Rides Thread

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              #7
              You shouldn't tighten things that much to stop leaks. If you have tightened it up with a 3/4, you could have cracked or torn out threads.

              Make sure the diff has the right oil in it, then if the threads are weeping a bit, use a bit of this on the threads.

              Just a little project im working on
              - http://www.lse30.com -

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                #8
                The manual calls for 41 ft.lbs. of torque on the bolts, so I don't think I'm at risk of over tightening by hand with a 3/4" wrench. But I totally take your point and agree.

                I think I'll try new drain plugs short-term. I'll get a hold of some thread sealer if swapping drain plugs doesn't work. Thanks for the feedback.
                91 318is Members' Rides Thread

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                  #9
                  Originally posted by Madhatter View Post
                  You shouldn't tighten things that much to stop leaks. If you have tightened it up with a 3/4, you could have cracked or torn out threads.

                  Make sure the diff has the right oil in it, then if the threads are weeping a bit, use a bit of this on the threads.

                  is that a plunger pump in that picture?
                  i'lldoitforacaravan

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                    #10
                    I know it's been a while, but the e30 hasn't seen a ton or road time to test... But I tried the thread sealant and it seems to have done the trick. Thanks for the help!
                    91 318is Members' Rides Thread

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