Drilling diff drain plug out

[PeterCrespin]

I hope the following may be useful.
Here is a pic of the (apparently square) diff drain plug on my car:

Why on hell using such an exotic size?

It is a nominal 1/2 cast (forged?) size I think, and slightly tapered to enable it to come out of the mould/die easily. The size across flats is probably slightly shorter near the tip of the square than at the base. It is a plumbing size to do with liquid handling (in this case oil retention in a casing). There are specialized male or female multi-spanners available with several square/pentagon/hex (?) drain / filler plug sizes each end. Google drain plug multi spanners or similar.

[ralphr1780]

Serge,
The drain plug in your pic is same as mine, probably an original one.
Check also the fill-in one on the back of the diff.
There are specific square spanners available in the trade, as Peter just said, but I have used the 12 points metrinch socket which is known to work on square and even rounded bolts.
Noticed that:
The diff cover, in which the fill-in plug fits is made of pressed steel. The plug can be screwed in relatively flush.
The diff block, in which the drain plug fits is made of cast steel. The drain plug will get quite tight a couple of mm before getting flush.

On a S1 you can lift the cover plate in the trunk to fit a tube and funnel for the oil filling while the car is standing horizontal on the floor.
On a S2 it an even more messy job because of no such access.

[paydase]

Pete and Ralph, merci.

Having also read other threads on the issue, I better understand my odd measurement and the unusual shape (tapered and probably diamond shape) of this filler/drain plug and the difficulty to find a suitable size spanner or socket.
The best tool to remove the plug, already mentioned by rolando, may be this socket, a high quality (albeit expensive) SAM product that can be sourced in the EU:
https://www.oscaro.be/fr/douille-1-2-de ... &p=5484952
If the plug is seized, such a socket with an extension is probably best fitted to undo it without damage.
A metrinch or 8-point socket are also good alternatives, but unless it comes easily, I would avoid a 14" simple spanner.
Thx also for the tip to access the plug for filling.
If I also understand correctly, there is no need to put any seal material when screwing the plugs back (in particular the drain plug), the tappered shape being enough. Am I right or is it better to add any teflon or similar tape?

[ralphr1780]

Avec plaisir Serge,
I did not use any Teflon tape, just proper tightening.
Will let you know in due course in case of sweeping!
My metrinch set is available for lending if you wish to.
Don't know which oils you will be filling, for my cars have opted for the highly spoken of Redline oils for gearbox+diff, ordered from a responsive company in Thimister-BE.
Btw: nice licence plate that you have!

[PeterCrespin]

I use Teflon tape on low pressure pipe or plumbing fittings (not brake fittings). Technically the taper does seal tight when dry but non-setting sealant or tape requires less force to seal and less force to undo. I think your PO who forced the plug and then powder coated the diff caused your problem. You should not need an expensive spanner to tighten or release if you use tape.

[mgcjag]

Im with Peter.....taper threads for plumbing always use sealer tape..in the old days hemp string and boss white