Lotus Elan

Mechanical brake switch (i.e. not hydraulic)

PostPost by: alaric » Tue Sep 23, 2008 11:22 pm

Hi all. I'm trying to fit the mechanical brake light switch to the back of the pedal box in my '72 +2S. I bought a new plastic switch. There's not enough clearance to install it with the pedal box in place. I've now managed to break the switch by taking it to pieces in an effort to avoid removing the pedal box - I've sealed the box in with sealants. So I need a new switch again. Is there a variety that can be put in without removing the pedal box?

Thanks.

Sean.
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PostPost by: mikealdren » Wed Sep 24, 2008 5:04 pm

Sean,
I don't know the answer but there are quite a few switches on the market, they all work in the same way, and many of them have the same thread fixing. The basic design was common to many cars in the 1960s. You could start at an Autojumble or a motor factors

Mike
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PostPost by: gerrym » Wed Sep 24, 2008 7:13 pm

Sean, pretty sure mounting thread is M12x1.25 (just measured my plastic switch ex SJS). You might want to try an industrial micro-switch.
Attached file is an example downloaded from RS components.
However, I'm afraid its very tight between inner fender and pedal box so you might have to resign yourself to loosening the mountings of the latter.
Radial solution would be to drill a large hole through the fibreglass fender!!!. One thing that might help a tad is to solder wires (flying leads) on to terminals and chop off the rest.
Regards
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MICROSWITCH0900766b801b827d.pdf
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PostPost by: gerrym » Wed Sep 24, 2008 7:19 pm

Sean, I meant to ask you for my own interest, which sealant you have been using.
As its a pretty critical to prevent water ingress, I've been using U-Pol Tigerseal with some success (plus it can be overpainted).
Regards
Gerry
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PostPost by: rgh0 » Thu Sep 25, 2008 7:25 am

As far as I can tell the original switch sufefreed from this problem as I beleive the switch in my plus 2 is orginal and I had to dismantle to remove t a few years ago.

I trimmed the end of the threaded section so I could refit without dismantling but its a tight fit

cheers
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PostPost by: mikealdren » Thu Sep 25, 2008 7:41 am

Gerry,
Are you sure it's metric? I would have expected it to be Imperial. The thread is usually plastic so it will easily deform to fit but I would have thought 1/2" was more likely?

regards
Mike
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PostPost by: Robbie693 » Thu Sep 25, 2008 9:06 am

Sean,

I have definitely removed and replaced one of these before without removing the pedal box. I can't remember if I dismantled the switch but probably did to stop the terminals scratching the inner wing as it was screwed in..

The cap with the terminals pops off and there is a spring and a washer along with the plunger inside - simple to put back together afterwards
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PostPost by: CBUEB1771 » Thu Sep 25, 2008 12:18 pm

mikealdren wrote:Gerry,
Are you sure it's metric? I would have expected it to be Imperial. The thread is usually plastic so it will easily deform to fit but I would have thought 1/2" was more likely?

regards
Mike


Mike is correct, the thread is 1/2-20. I fitted a thin lock nut to mine and 1/2-20 is what fit.
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PostPost by: gerrym » Thu Sep 25, 2008 5:01 pm

Mike, I agree original thread is probably 1/2" 20tpi and as most of the car is threaded UNF/UNC then this would make sense. (there are however metric threads lurking around such as the later Girling brake calipers, dampers etc).

The switch I was supplied with is however almost certainly a modern plastic replacement and non-original. It performs the original function. Measured thread OD is 12.05mm (so pretty loose fit for 1/2" UN)

Difference in thread is almost academic for a non structural application. Thread "pitch" for a 1/2" 20tpi is afterall 1.27mm as opposed to the 1.25 of the metric thread.

My point is that if a slimmer replacement "micro-switch" is being contemplated, then perhaps perhaps a metric threaded alternative might be available, that would ease the original stated problem. ie lack of access space without removing entire pedal box.

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PostPost by: alaric » Thu Sep 25, 2008 10:22 pm

Wow, so many replies. Thanks guys.

The thread is indeed half inch unf 20tpi. I bought a couple of bolts from eurofasteners to clean out the thread in the pedal box.

I've managed to fit the body of the switch with no problem, but in taking the switch apart to get it to fit I managed to crack the part that pops out. So I could just get another one and hope I don't break it again. Or I could bite the bullet and pop the pedal box out again - it needs to come out completely so I can clean the surfaces off again.

For the pedal box I've used a sealant from Halfords - I'll take a look when I go out to the garage later on. The main problem with it is once set it's not easy to remove the box again. It's a bit like silicon sealant but is intended for auto applications.

Another option is to use a hydraulic switch instead - I happen to have one that could pop into the line from the master cylinder. I think I prefer the non hydraulic one though as it'll come on as soon as I touch the pedal.

As soon as I remember to pick the phone up and order a switch I'll get on with it.

All the best.

Sean.
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PostPost by: Craig Elliott » Fri Sep 26, 2008 6:59 am

Just in case you weren't aware, the switch is the same as that used in the original Mini - which may help in finding cheaper sources if you break one again. They are a tight fit but some gentle adjustment of the electrical connectors should allow you to fit it OK.

C
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PostPost by: alaric » Wed Oct 01, 2008 6:25 pm

Thanks. I've got my new switch now so'll try fitting it later tonight. Hope it goes in ok this time.

All the best.

Sean.
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