Classic cars forum & vehicle restoration.

[ukdave2002]

As previously reported I had to replace the Brake Lamp switch on the Mini, these hydraulic switches were fitted to many BMC vehicles from the 50's to the 90's.



My father had switches that lasted less than 12 months on his Morris 1000 in the 90's and 00's, the engineer in me was curious to understand why it had failed, so I opened it up.





As you can see there is not much to go wrong, the reason it failed was both the contacts and the disc had oxidised. There was a very slight sign of brake fluid contamination, possibly this, and with a lack of use may have promoted the oxidisation?

[alastairq]

Brake fluid [ dot 1,2,3 &4] is hygroscopic.

It sucks water [moisture] from the atmosphere like a dementor's kiss.

Even if we assiduously try to keep our atmosphere out of things.

{Seems it might even suck moisture through rubber?]

Since those switches are, essentially, sealed for life...[even if only a very short life?] ..I have no idea what substances could be introduced into them to keep those contacts clean?

Perhaps if someone had designed a rotating contact disc, which swivelled at each brake application, thus cleaning the contacts, I don't know the answer.
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Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

[consul 57]

good pics, at least you can get them easily enough, when mine went my local motor factor got me a new one in a day or so.