Sealing Gearbox Drain Plug

[John P]

Hi,

I seem to have an ongoing, and very noticeable, leak from the gearbox drain plug (3-speed box).

The brass plate which goes around the plug and also locates in the hole at the bottom of the bell housing is currently up against the gearbox casing with the fibre washer between this plate and the plug.

Firstly is that correct and secondly should I try annealing the brass plate as presumably this is effectively acting as a seal against the gearbox casing.   I'm assuming the fibre washer should prevent any leakage between the plate and the under-head face of the drain plug.

I guess I could try PTFE tape around the thread but I'm not really happy with that as when the plug is removed you're likely to leave fragments of tape in the female thread which could find their way into the gearbox.

John.

[Steve Jones]

You need a fibre washer either side of the brass plate.

Steve

[AustinWood]

The gearbox drain plug I believe has a longer threaded portion to allow for the second fibre washer.

[Robert Foreman]

There should be a paper washer followed by the brass plate followed by the plug  with a fibre washer.

[squeak]

I use a fiber washer that has an internal diameter smaller than the plug, so that it forms an interference fit with the root diameter of the plug thread. Assembly order is gearbox sump plug, brass plate, then wind on the fiber washer and fit. Choose the thickest red washer available and if plug length is insufficient or the hex burred, I believe there are longer steel plugs.

[David Grear]

Are you sure it is the gearbox drain plug and not the rear main?

[John P]

Yes, it's definitely the drain plug and became more significant after I changed the oil.

I was confused as on suppliers lists the number per car for the fibre washer is shown as one.

I think that two of the washers I have will leave very little thread engagement so am tempted to follow the suggestion of a gasket paper washer between the box and brass plate.

[Colin Morgan]

If you are pushed for sufficient thread, do you need the brass plate?

[Parazine]

There should be a paper washer followed by the brass plate followed by the plug  with a fibre washer.

This is definitely correct. Most often not implemented properly in the past.