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  #1  
Old 12-04-2009, 09:03 PM
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What size is the Hex For the differential drain/fill plug 1985 300D

For the differential on a 1985 300DT?

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  #2  
Old 12-04-2009, 09:06 PM
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More than likely a 14mm.
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  #3  
Old 12-04-2009, 09:13 PM
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Yep.... It is an H14.

I actually started removing my old diff. today (in the pouring down rain).
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  #4  
Old 12-04-2009, 09:33 PM
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The plugs have been known to be a little tight on occasion. Somewhat normal actually. So make sure the hex is well cleaned out to allow your tool to bottom before application of pressure.

Remember it is standard proceedure to loosen the upper plug first if changing the oil. No sense finding you have drained the differential and cannot get the top plug out to refill with the tools you have on hand.

This said yours will almost fall out. If I did not mention it you would swear the casting was going to break before it let loose.
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  #5  
Old 12-04-2009, 10:04 PM
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I had to get a jack under my breaker bar to get it loose.
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Old 12-04-2009, 11:05 PM
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Quote:
Originally Posted by ::matthew View Post
I had to get a jack under my breaker bar to get it loose.
I had to do the same thing. I fought with that plug for the longest time before just using a jack. Is there some explanation for why that upper plug is always so hard to remove, yet the drain plug usually comes out pretty easily?
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  #7  
Old 12-04-2009, 11:10 PM
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What do you suggest using for oil?
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Old 12-04-2009, 11:18 PM
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I used Lucas 90 weight, I think.
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Old 12-05-2009, 01:41 PM
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Originally Posted by swheele2 View Post
. . . Is there some explanation for why that upper plug is always so hard to remove, yet the drain plug usually comes out pretty easily?
My guess is that there is always a supply of oil, perhaps seeping slowly through, keeping the drain plug moist with oil and therefore water and corrosion at bay. But on the upper plug, it is not exposed to oil so water and corrosion are getting a better shot at it.

I wet my plugs down with PB Blaster as I was getting set up to do the differential cover resealing project. By the time I went at the plugs, it had penetrated and gave me an advantage. I also put a two foot piece of pipe on my 14MM wrench which gave me some added leverage. I do not think I would have broken them loose without the leverage of the pipe.
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Old 12-05-2009, 01:52 PM
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What do you suggest using for oil?
I used Valvoline Duro Blend 80W-90 Synthetic. It looked like the best stuff on the shelf and I don't mind spending a little more when it is something that is going to be in service for such a long time.

I also bought a pump to get the oil into the differential. It did not work though. Dang, was that every annoying. I got as much oil as I could into the diff but was not able to get the whole quart in. I will need to take it back and get another one.

In theory, I suppose with a helper you could get about 3 or 4 feet of clear plastic hose with a funnel fitted to the upper end and have a helper pour the oil down the tube while you hold the other end in the filler hole. You would need to pinch the upper end and raise the hose up over the diff, under the car as it was emptying. Sounds like it would work.
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85 300D 72K Anthracite Grey (Rutherford) 0-60 in 13 seconds
84 300D 331K Black (Rufus) 0-60 in 14 seconds (adjusted the ALDA)
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 22K
98 Ford Taurus 62K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
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  #11  
Old 12-05-2009, 04:26 PM
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Originally Posted by RML View Post

In theory, I suppose with a helper you could get about 3 or 4 feet of clear plastic hose with a funnel fitted to the upper end and have a helper pour the oil down the tube while you hold the other end in the filler hole. You would need to pinch the upper end and raise the hose up over the diff, under the car as it was emptying. Sounds like it would work.
This is what I did on the second one. The first I used a one foot hose and was successful, but took a long time.
The second one, I also had the helper cut a breather hole in the bottom of the plastic container, much faster.
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Last edited by toomany MBZ; 12-07-2009 at 08:26 PM. Reason: spelling
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  #12  
Old 12-05-2009, 11:01 PM
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When you replace the upper plug, put some anti-seiz on it.

Charlie
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Old 12-07-2009, 11:20 AM
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Post #75 shows how I used an old gas line anti freeze bottle . . . no helper needed!

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  #14  
Old 12-07-2009, 04:27 PM
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Quote:
Originally Posted by RML View Post
My guess is that there is always a supply of oil, perhaps seeping slowly through, keeping the drain plug moist with oil and therefore water and corrosion at bay. But on the upper plug, it is not exposed to oil so water and corrosion are getting a better shot at it.
That does make sense. I had always assumed the oil was splashing around in there enough to keep oil on the upper plug, but I suppose an occasionally splash of oil isn't enough to seep down into the threads.
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  #15  
Old 12-07-2009, 04:38 PM
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hit it with PB Blaster or other kerosene product the night before, then drive the 14mm socket in with a BFH (big ****** hammer). A few good straight on hits are usually enough to bust it loose. Use an extension...and yeah, it seems like you're gonna break the differential casting before it breaks loose.

If that doesn't work, you'll have to apply heat around the plug.


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