Seals on Herald disc-brake master cylinder extension

[Colin Lindsay]

I'm actually getting to the stage where I'm fitting things like this, but need to know if there are any seals on the master cylinder extension tube that was fitted to drum brake conversions. I'm going to cheat with the convertible and use a bigger master cylinder as fitted to later models but this one has the original setup and I want to try to keep it, but don't want any fluid leaks. The exploded diagram of the extension shows one seal which looks to be for the top filler cap:

However is there one lower down where the metal collar screws onto the master cylinder? There are two possible options here: a seal on top of the plastic lip which is tightened by the metal collar, and no seal underneath where the plastic tube sits into the alloy cylinder, or is there a seal between the plastic and alloy, and none under the metal cap itself, which would seal against the plastic lip. Or maybe both?

 

 

 

 

[Casper]

Between plastic and alloy.  nothing under the metal cap. 

https://www.demon-tweeks.com/uk/girling-integral-master-cylinder-extension-reservoir-r-p64475476/

C.

[Colin Lindsay]

Gosh durn it!

Now mine has to come off again... so I can move the seal UNDER the lip and not on top... I jumped the gun slightly.

Are the seals available new? Mine aren't bad but I'd like to replace it for peace of mind.

[Casper]

I have, in the past, had trouble finding seals (also serious rust on the metal and damaged plastic cap) which is why I made a mental note of the DT advert.  I fortunately picked up a NOS item for a decent price so I am sorted. No doubt a suitable O-ring would serve.  I will have a look in the workshop as I may have something squirrelled away.

C.

[Colin Lindsay]

1 hour ago, Casper said:

I have, in the past, had trouble finding seals (also serious rust on the metal and damaged plastic cap) which is why I made a mental note of the DT advert.  I fortunately picked up a NOS item for a decent price so I am sorted. No doubt a suitable O-ring would serve.  I will have a look in the workshop as I may have something squirrelled away.

C.

I bought one of these NOS from Mick Dolphin back in the early 1990s but have never used it, but on checking it for this car it has no seals at all bar the one under the plastic cap.

As luck would have it, my nephew called over yesterday and has taken one of the extensions off to the Engineering Works to find suitable o-rings. One for under the lip is a necessity, but I'm wondering if a flat seal under the metal cap, and on top of the lower plastic lip, might assist in sealing as well as preventing wear? 

 

[Casper]

That's a possibility but doesn't that assume the screw thread provides a fluid seal? 

[Colin Lindsay]

The plastic extension fits down into the alloy cylinder by half an inch or so, then there's a lip which the metal cap tightens against to crush the rubber seal against the outer rim of the master cylinder. I suppose the way that it fits inside the master cylinder, and the shape in which it's moulded especially with the o-ring properly fitted provides enough of a seal by itself, and so the fluid shouldn't reach the metal cap at all. In all probability it doesn't require anything further.

Now that I've typed that down it makes sense that nothing else is required; similarly I was wondering last night if I should use any kind of grease on the alloy threads to prevent the metal cap from seizing to the alloy of the cylinder, and now I'm thinking: why? It doesn't need to be removed as any filling is through the top plastic cap. Thinking too deeply, as usual...

[Casper]

Quote

 I was wondering last night if I should use any kind of grease on the alloy threads to prevent the metal cap from seizing to the alloy of the cylinder, and now I'm thinking: why? 

Dissimilar metals and moisture = corrosion.  I think I lacquered both the MC and the steel cap, but grease might hold it back for a while.

C.