Stuck differential drain bolt

Joined
Aug 15, 2009
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Colorado
Hey gang,

Looking for advice. I’m changing the front and rear diff fluid on my 2008 Subaru Forester. The Subaru dealer was last to service them and the bolts are seized on. I was barely able to get the front diff drain plug off. I’m down to the rear diff and I was able to loosen the top fill plug after a night soak of PB Blaster, but the bottom drain plug won’t budge. The drain plug has had three long PB Blaster soaks and now heat from a torch. It still won’t budge and is rounding out.

I’m just about ready to bring it to a shop as I’m out of ideas. Before anyone asks, yes I’m using the correct 13mm socket. I have all new replacement plugs too because these are all rounding with the torque needed to take them out. Anyone got anymore ideas before I give up?
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Joined
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Missouri
I apologize for a lack of direct knowledge, but is that a separate cover that the plugs go in to?

If so, I would consider replacing the cover, or take it to the dealership and let them undo their handy work so that it's covered by a warranty if they decide to break out the impact gun and ugga dugga the plug out and it cracks the cover.
 

Soobs

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I apologize for a lack of direct knowledge, but is that a separate cover that the plugs go in to?

If so, I would consider replacing the cover, or take it to the dealership and let them undo their handy work so that it's covered by a warranty if they decide to break out the impact gun and ugga dugga the plug out and it cracks the cover.
I’m not sure what you meant by a cover? The plugs are screwed into the back of the differential. There is no cover on the plug itself. It’s just what these type drain plugs look like for Subaru. See the pic below. It’s not going to be warrantied as I no longer live in the state the work was performed.

As a temporary fix I could take the fill plug out, pump out the fluid, and refill, but I’d like to get it all squared away eventually. I just can’t believe how stuck this drain plug is.
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Joined
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Taking it to the dealer who did the last service is a good option.
I would use a long 1/2" breaker bar with the 3/8" adapter and use my body weight to break torque.
Good luck.
 

Soobs

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Taking it to the dealer who did the last service is a good option.
I would use a long 1/2" breaker bar with the 3/8" adapter and use my body weight to break torque.
Good luck.
I am using a 1/2” breaker bar with the 13mm socket (the size of this square). That’s how it started to round. 3/8” adapter is closer to 10mm square and too small.
 
Joined
Nov 1, 2011
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New Jersey
I always tried to tighten the plug a bit to break it loose.
It'll snap loose. If not a bit of heat and a fresh impact extension.
Be sure the 3/8 square hole is clean and debris free.
 
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Apr 25, 2017
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Ohio
Another member here, with a Subaru, had this same issue maybe a year ago. I think it went on for days or longer and the person ended up taking it to a shop that either broke it loose for or just did the differential fluid replacement job for him.
 
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Joined
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I am using a 1/2” breaker bar with the 13mm socket (the size of this square). That’s how it started to round. 3/8” adapter is closer to 10mm square and too small.
You are right. 13mm = 1/2". My mistake.
As others have said, make sure the hole is clean.
Good luck.
 
Joined
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Daytona Beach
Drill it out, then make two cuts from the inside of the drilled hole out toward the threads. Don't get into the threads with the saw. Take a small chisel and knock the little notch you made, into the hole you drilled (NOT into the diff.) The other portion will come out very easily after the tension is removed.
Get a replacement drain plug first of course. I make the cuts angle like so \ / with the thin part toward the threads.

In fact, one cut might do the trick, just to give the threads some relief from the excess tightning.
 
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Texas
I wanted to drain BMW diff with no bottom plug, so I made a suction tool from a plastic gallon dispenser and small bendable cooper tubing. Might work here if there's some open space inside.
 
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When I look at your first pic, I looks like there is some sort of thread lock or heaven forbid, JB weld on the threads. There is some of the same material on the case beside the plug, like some sort of glue. I'd definitely heat it, then use impact while it's hot. In case some sort of thread lock was used.
 
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JC1

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To the OP I would back off for now because without the proper tools you are gonna get into a mess like @Hall mentioned.

Not sure if you have another car to drive If you make a mess of that drain plug.

@Trav always had great advice, he's saved my butt a few times.
 

Astro14

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If the dealer did this, let them "undo" it.

By cover, people mean a differential cover, as opposed to a single piece housing. You have a cover. Worst case, it can be unbolted and replaced, with new plugs.

If it were mine, and out of warranty, and I wanted to fix it myself, then I would buy a new 13m drive and two new plugs. Heat, lots of heat, on the cover to soften up whatever gunk is on those threads, then hit it with an impact.

Always do the fill plug first. If that won't come out, you can't do the job at all. Stop there. At least there is some fluid in the differential. If you loosen the drain plug, and drain the fluid, then find out that you can't get the fill plug out, you're up a creek. You have an empty differential and a sidelined vehicle.

But all that is future advice, I would let the shop that did this fix their crap work first.
 

JHZR2

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My Mercedes cars have similar plugs with a 17mm hex. They can be so stubborn that I need to have a cheater bar and press with my legs. Nothing helps, even antiseize, it’s an electrochemical phenomena. FWIW, I never tried something like Teflon tape….

I have found better success using an impact on these stubborn plugs. And, like any female fastener, make sure the plug female end is extremely clean, the tool is seated fully, and the fit is tight.
 
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