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Can't Remove Differential Fill Nut 78 280Z


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After draining the differential for routine service, I can't loosen the 17mm fill plug in order to replace the fluid.  I've soaked it with penetrating fluid,  taped on it with small hammer, used a dead blow hammer and a "cheater" pipe but to no avail.  Can I use some heat from a butane torch to heat around the nut without damaging the cover gasket?  

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13 minutes ago, Mayolives said:

After draining the differential for routine service, I can't loosen the 17mm fill plug in order to replace the fluid.  I've soaked it with penetrating fluid,  taped on it with small hammer, used a dead blow hammer and a "cheater" pipe but to no avail.  Can I use some heat from a butane torch to heat around the nut without damaging the cover gasket?  


It is common for the steel plugs to get stuck in the aluminum diff housings. Also common on the transmission. Borrow or buy an impact wrench. Electric if you don’t have an air compressor. That’s your best bet.

 

You can warm up the housing with a torch but you might burn the diff oil inside which will stink pretty bad. Be careful not to burn the gasket from the inside-out. AL expands roughly twice as much per degree as steel, so this should work. 
 

Torque spec is 25lbs when retightening so don’t get carried away. 

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Tom, a couple of alternatives to using the fill nut, provided for your consideration:

1) Remove one side axle and fill the diff through the side.

2) Remove the breather on top of diff and fill through the breather hole.

 

These two methods don't give you the ability of checking fill level via the fill hole; so you will need to verify fill level some other way (e.g. visual inspection from top or side...a small borescope camera can be very handy for these types of tasks.)

 

Regarding application of heat...should be fine if you just keep the heat on the plug itself (vs the AL cover).  Wrap the outside of the cover (in the vicinity of the gasket/seal) with a wet towel to minimize heat buildup in the are of the gasket.  Typically have to apply a couple of heat cycles to break up any oxidation that's built up in the threads over time.  Good luck with it.

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Heat works well.  If you have a heat gun you won't have to worry about leaked oil or undercoating catching on fire.  But, people use torches to remove that plug all the time.  It makes a big difference.  You don't have to get it red hot, to where the fluid or gasket get damaged.  Focus the flame around the plug but not on it.

Edited by NewZed
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You know we have all been there when you get three similar responses to a problem within a few hours 😂

 

when I was young and dumb(er), I once lowered my car onto a breaker bar to loosen the tranny fill hole. 

 

I don’t have a dedicated full hole on my r180 cover (from a Subaru STI) so I drain completely then fill with a specific volume from the axle shaft hole. The spec is easy to find with a quick search online, or from any type of service manual. 

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All the above advice well taken.  I do have all the bells and whistles, ie: air, impacts, too many tools and Datsun stuff all around.  I've yanked and tugged on a many R180/200 diff and trans plugs for longer that I'll admit but never had to use heat to make one move.  Perhaps I'm now just getting too weak.  I'll use some heat, with the precautions stated, and fell better than making a bone head move without asking for advice first.  Never too old to learn new tricks!  Thanks.

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  • 3 weeks later...

(here I go again...)

 

AND - there is NO reason to tighten either the drain OR fill plug on either the diff or transmission tightly! THERE IS NO PRESSUE INSIDE.

Use teflon tape on the threads (3 or 4 wraps). Install the plugs snuggly (I sure as hell would NOT go 25 ft/lbs - not necessary) - ONLY TIGHT ENOUGH TO STOP LEAKAGE (of a viscous fluid that's not pressurized...). Hope that past installation hasn't damaged the cover plate threads.

 

Next time you'll remove and reinstall these plugs without any drama.

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Follow-up on the differential fill plug that I could not remove.  I followed some of your advice and heated the AL case.  I tryed to not put direct heat on the plug itself. I did this several times (cycles).  Then again used my 20" cheater pipe on the open end wrench and finally out it came.  After refilling it with Synergyn gear oil, all is well!  Thanks for the help.  

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