8 3/4 Vent is leaking?

Engine, Trans & Driveline

  1. 493 Mike

    493 Mike FBBO Gold Member FBBO Gold Member

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    Hi fellas,
    The vent itself is leaking gear oil right out the cap and of course all over the housing, shock, and fuel tank.
    I have had it out twice and Teflon taped the threads (seems OK), and cut small plugs out of porous foam to insert in the bolt bore-with no luck.
    Lube level is below the fill plug.
    741 case.
    The bolt will hold a vacuum when a vacuum is applied to the bore.
    I have never seen this condition before-any thoughts?
    Mike
     
  2. chtampa

    chtampa FBBO Gold Member FBBO Gold Member

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    In 69 the sure grip throws oil onto the vent and it blows out. The fix for it in 70 was to move the vent a couple inches away from the carrier. My fix was a small puke bottle with a hose on an old vent with the metal cap removed and it drips back in when you park.
     
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    • Fran Blacker

      Fran Blacker FBBO Gold Member FBBO Gold Member

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      Don't know thread size but if you make it an inch or two longer could help. Would be nice to find the root cause.
       
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      • oldbee

        oldbee FBBO Gold Member FBBO Gold Member

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        Never heard of such a thing, w/o an overfill. Still thinking.
         
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        • Fran Blacker

          Fran Blacker FBBO Gold Member FBBO Gold Member

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          What about wrong lube. Foams up and drips out vent. Is this recent after some rear end work and changing lube?
           
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          • 5.7 hemi

            5.7 hemi FBBO Gold Member FBBO Gold Member

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            How in the hell can the sure grip throw oil onto the vent nipple? It’s nowhere near the sure grip, plus it would have to get by the side bearing. Not buying that.

            When you filled the case with lube, did you do it with the rear hanging down? If so, you’ve got too much fluid.
             
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            • halojumper

              halojumper FBBO Gold Member FBBO Gold Member

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              That's an odd problem I have never heard of before. Like 5.7 hemi said.
               
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              • Cranky

                Cranky Banned Staff Member FBBO Gold Member

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                Can you put a hose on the vent and tie it in a loop? Your problem isn't real common but I've heard of it before. Something is generating heat to make the rear end oil get too hot and expand. Do you have a temp gun to see how hot it's getting? Rear ends can produce heat in the 180* range. Are you towing with it? How much below the fill plug is it cold? I like to fill them up to the fill plug....
                 
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                • khryslerkid

                  khryslerkid FBBO Gold Member FBBO Gold Member

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                  Made that mistake once, filled it with the rear hanging. Front seal kept leaking. Checked it with the rear up and all kinds of fluid came out. Doesn't leak anymore.
                   
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                  • chtampa

                    chtampa FBBO Gold Member FBBO Gold Member

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                    There was a TSO, if that is the right term for it. The lube for clutch style sure grip was NOT to be used because of foaming and the vent leak. I understand that the current lube choices have additives that irritate the issue. I removed my clutch style sure grip and installed an NOS 69 spring style unit and did nothing else and the leak started. I tried 3 different vents and the lube was measured according to Service Manual. A loop will act like a sink with no vent and blow air through the hose.
                     
                  • Lefty71

                    Lefty71 FBBO Gold Member FBBO Gold Member

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                    Have you tried running a tube up to the frame like a 4x4 would have, just to see if it stops??
                     
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                    • 5.7 hemi

                      5.7 hemi FBBO Gold Member FBBO Gold Member

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                      The only way this vent is puking is that the vent is plugged or too much fluid. I’m guessing too much fluid.
                       
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                      • mopar 3 B

                        mopar 3 B Well-Known Member

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                        I have pulled trailers using 69 housings with sur-grips and never had a problem. What you using for lube? The foam sure would not do it any good, filled with grease or what ever was put in it and it surely will not vent.
                         
                      • Mopar Hunter

                        Mopar Hunter Well-Known Member

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                        I had the same situation but mine was the brakes lines going into the Y adapter that was leaking. This was on my 8-3/4 rear.
                         
                      • Kern Dog

                        Kern Dog FBBO Gold Member FBBO Gold Member

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                        Oooops. That is the way that I always do it.
                        Son of a bitch.
                         
                      • 5.7 hemi

                        5.7 hemi FBBO Gold Member FBBO Gold Member

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                        The Dana 60 I narrowed for my buddy was puking diff fluid. He got an aftermarket diff cover and filled it with 4 1/2 quarts and then I get a call, “why is my Dana covered in diff fluid”? Well it turns out the he filled it with the car jacked up and diff hanging. The cover allowed an extra qt. of fluid but since this is a truck Dana 60, the axle housing allows diff fluid to flow into the tubes to lube the bearings. But he used way too much and no other way for the fluid to vent once it got hot. I said he needed to jack up the rear to where it’s just making the car come off the stands and drain it. Then fill it with 3 qts. of fluid. He did it, now no puking out of the vent.

                        So yes, too much fluid, especially on an 8 3/4 will puke out the vent as there is nothing to let the fluid flow into the tubes as easily as the Dana.
                         
                        Last edited: Jun 30, 2019
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                        • 5.7 hemi

                          5.7 hemi FBBO Gold Member FBBO Gold Member

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                          I must correct myself. The 8 3/4 housing isn’t like Dana 60 or GM 10/12 bolt. The bearings are on the center section and that allows the fluid to move freely into the tubes as there is nothing blocking the opening. So fluid can move into the tubes and if you don’t have the inner seal, will wash out the bearing grease and eventually leak at the ends.

                          So the OP’s problem may still be too much fluid, but could also be a messed up vent.
                           
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                          • miller

                            miller Well-Known Member

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                            Is the vent itself clear? Usually, turning the 'cap' will clean anything in there. Vent is needed for a reason.
                            Before I put one in the housing, after cleaning it, I always blow air though it.
                             
                          • 493 Mike

                            493 Mike FBBO Gold Member FBBO Gold Member

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                            Thanks for the ideas fellas! I think I'll try a hose extension with a loop. I did change the lube but, it appeared that the problem has been around for a while before I bought the car. PO "babied" the car for 30 years before me and I just got back from a 250 mile trip-at least 30 miles of which were at 80 mph.
                            Mike
                             
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                            • chtampa

                              chtampa FBBO Gold Member FBBO Gold Member

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                              A loop wont let the fluid back in. It will store it and when it is full it will blow out again. Physics.
                               
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