Herald disc brake cylinder extension seal

[Colin Lindsay]

Morning all! (Much too quiet in here)

I've converted both Heralds to disc brakes which requires either an extension to the master cylinder reservoir or else a bigger master cylinder. I can get the master cylinders, part number GMC220 from £34.50 up to £70, essentially the same item but just some suppliers have more expenses than others.

For the sake of it I'd like to try to source the seals for the original master cylinder extensions; I have two NOS versions, one with a seal and one without, but the seal I do have has been dry-fitted to a master cylinder and has become distorted after 20 years or more. I can find the part numbers for the extension and the cap, but not the seal which is not even shown in the parts manual. It's a square profile seal and fits between the bottom of the extension and the master cylinder top edge.

Does anyone have a part number for it, or a possible source? It needs to be perfect as otherwise fluid will leak onto the paintwork.

  

 

 

[Clive]

You can buy square section O rings in a huge variety of sizes, metric and imperial. So somebody should sell a suitable size. As to material, Nitrile is definitely no use, I think Viton may work....

This is assuming you can't buy the proper seals. The extensions are still available though, from motorsport suppliers.

[Colin Lindsay]

23 hours ago, clive said:

This is assuming you can't buy the proper seals. The extensions are still available though, from motorsport suppliers.

Aha... if they're available, the seals should be too. Must have a search.

Ok.. lot of square-section o-rings available; thing to do now is to work out the size, and the most suitable material.

I was intending to maybe invest in a small hone to clean up the cylinder bore; it has to be about 14/15mm but not at the price I've found:

It's going to be a long time until Santa comes again...