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Discussion Starter #1
This should probably be posted in another section but people here is generally quick to answer.

I have read many responses on the filler plug size. And they all says it is a 12mm hex. However I have a 12mm allen key but I think it is a very loose fit.
The hex "hole" in the plug is close to 12.5mm which is close to a 1/2" size instead.

Have anybody tried with a 1/2" hex key instead of the 12mm? I am worried that I will destroy something if I try to use the 12mm because of the loose fit. The plug will demand some "persuasion" to come loose.

Regards
Jens
 

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IAP sells hex wrenches for the diff and gear box. Their ad says the following:

Hex Head Wrenches

"If you own an Alfa or Fiat, you'll need a set of these! 1973-on Fiat twin-cam cars use 10mm for cam covers. Fiat oil pans and gearboxes use 12mm. Fiat rear differentials use 14mm. Alfa Romeo gearboxes and differentials use 12mm or 14mm filler plugs. Check your car before ordering."

Sounds like your car might need a 14 mm
 

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Discussion Starter #3
Thanks for your answer Lokki.

Unfortunately it cannot be 14mm. That would never fit. I meaured the plug with calipers and got it to 12.5, which is too much for a 12mm but might be slightly too small for a 1/2 inch which translate into 12.7mm.

When I try the 12mm allen key it feels just like when you got mm tool instead of the required inch (or vice versa). "This is not right but it might work anyway".
 

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I might of inquired about a similar question a while back but never got around to topping off my gearbox and diff. What size exactly hex is needed for a S3 spider filler plug ('90 Quad)? I believe someone stated 12mm but want to make sure.
 

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12.5 would be awful close to 1/2". You can test it by inserting a 1/2" bolt head or nut to see.
 

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replace it

Wonder if "The Curse Of The Previous Owner" is in play here.

In case you need a new one after you get that one out.

GB062 OIL FILLER PLUG - GEARBOX AND DIFFERENTIAL - Classic Alfa
I would definitely recommend replacing any drain plug (once you get it out) if it is found to be worn past the point of making a solid fit with the correctly sized wrench. You never know which removal is going to be referred to later as "the last time you were able to get it out without drilling or cutting it"...
 

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Original brass ones are here. Much better than plated steel as they are kinder to the threaded hole in the diff/gearbox case. Please email/PM me if interested, thanks.
 

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Works for me.

I need to leave a better trail of breadcrumbs so folks can effectively use "search" to take advantage of my (and others) experiences.

Here's a recent picture of a chisel I had to grind slightly on all faces to fit in the tranny and diff plugs. I had modified the chisel before, but later flattened the end with vigorous hammering. And don't even think about shortening a chisel with a hacksaw. All I know for sure is that is a 13mm box wrench fitting a little loosely on the chisel body, which would of course make the plug opening just slightly smaller than 13mm.

And as a plus, you get a spare chisel. Can't have too many of those!


I also made a point of cleaning both plugs thoroughly and using some fine sandpaper to clean both sides of the washers.

Best wishes.
 

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depends on your year,it might be easier to just shift the center console and pour the oil into the tower,easover than squeezing your bbody under the car and trying to pump that thick oil up into the gearbox
 

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Discussion Starter #12
I happen to have the diff dissembled so today I took it to a well sorted hardware store. Fortunately they had both 1/2" and 12mm hex socket so I could try.
Results were that the 12mm fitted just as awful as my own allen key but the 1/2" wouldn't fit. Note the 1/2" was very close to fit. I could probably jam it in there but then I would never get it out again.


Just to explain. My filler plug is not worn by any means. It is an original brass one with no previous marks. I wouldn't be surprised if this was the first time in 20 years that anybody tried to remove it.

The original part was simply made with very odd measurements.

The best would probably be to buy the 1/2" and file it down a few tenths of a mm. That result in a very snug fit. However I bought the 12mm socket and used it with an impact wrench. I couldn't get the plug to move with the allen key. The impact wrench solved it. I dialed down the air pressure a bit to be gentle. The knocking motion apparently loosened it. I was worried all the time the socket would slip due to loose fit in the plug.
 

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I seem to recall my wrenches always being a little looser than I expected in the plugs.

As long as you use a copper washer and torque to spec with a torque wrench I wouldn't expect any issues.
 

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I seem to recall my wrenches always being a little looser than I expected in the plugs.
Mine too. My Spider is on the lift at the moment so I checked the differential fill plug and the 12mm Allen wrench is a loose fit but I have had no problems with it. I always anneal my copper washers when I re-use them so they are soft and do not need a lot of torque.
 

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Ed,

Are you going to make us look up "anneal"? :)
 

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Discussion Starter #17
Ok so I had to look up "annealing".

Ripped this from wikipedia.

"Annealing, in metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and to make it more workable. It involves heating a material to above its critical temperature, maintaining a suitable temperature, and then cooling. Annealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.

In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper, silver[1] and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming."


So we learnt something new today.

Thanks.
 

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the deal here is that is a cast plug. that hex isn't machined... and , as such doesn't have perfectly square sides... they have a slight taper to them where is is a little smaller at the bottom and a bit wider at the top. and the depth is such to allow a lot of engagement with the presumption being that you are only applying enough torque to crush the washer and seal it rather than try to preload the threads... think about it... you have a very large dia steel plug going into only a few aluminum threads. to have something "tight " you are actually stretching the fastner by virtue of the shear forces on the threads ( preload ) . the force necessary to stretch that plug would tear those threads out in a heartbeat... so... in the alternative you are relying only on the frictional forces at the washer. how much force do you need for that ? not much. so a marginally loose fit of the allen wrench is presumed to be no big deal because the forces are low. if you are worried about it falling out, drill it and safety wire it .
 

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the deal here is that is a cast plug. that hex isn't machined... and , as such doesn't have perfectly square sides... they have a slight taper to them where is is a little smaller at the bottom and a bit wider at the top. and the depth is such to allow a lot of engagement with the presumption being that you are only applying enough torque to crush the washer and seal it rather than try to preload the threads... think about it... you have a very large dia steel plug going into only a few aluminum threads. to have something "tight " you are actually stretching the fastner by virtue of the shear forces on the threads ( preload ) . the force necessary to stretch that plug would tear those threads out in a heartbeat... so... in the alternative you are relying only on the frictional forces at the washer. how much force do you need for that ? not much. so a marginally loose fit of the allen wrench is presumed to be no big deal because the forces are low. if you are worried about it falling out, drill it and safety wire it .
Amen brother... you don't need a breaker bar to tighten this plug..this is the cause of most problems. No tighter than a spark plug... Like 1/4 turn.. if it weeps your copper washer needs annealing/quenching..
 

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Stevesxm,

Thanks for your informative comments on the dynamics of our tranny and diff plugs. Your words make a lot of sense in regard to the "righty-tighty" aspects of the situation.

As you are aware, however, the major issue faced by many owners, myself included, has been the "lefty-loosey" challenge, accompanied by a nagging fear the removal tool is going to turn within the plug.

Once removed, and the washer annealed, a firm but gentle hand on re-installation should, as you wisely observed, mitigate future headaches.

Best wishes.
 
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