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brake switch


Andy A
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Confused. . .

Not aware of brake light switch that crews into the 'line' ... Autocorrect problem?

As far as I know there are two types of switch, one in the cabin that rests against the pedal and only makes a circuit when the pedal is pressed - earlier type - with and without servo, single circuit brakes (I think)

later type - for dual circuit servo brakes, sits on top of the pedal box in the engine compartment, a bugger to set right, as if you screw it in too far it will brake when you press the pedal.

The only other switch I can think of is the pressure differential warning apparatus - down on the chassis rail and only on dual circuit brakes.

Any photos?

G.

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Series 2 vehicles originally had a pressure switch plumbed into a 5 way junction unit (1 inlet from the master cylinder, 1 outlet to each front brake, 1 outlet to the rear axle, and 1 for the pressure switch).

brake_light_switch_HL2.jpg

It was the later versions of the Series 2A that had the switch, mounted in the cabin, resting on the brake pedal.

brake_switch-1.jpg

It was the Series 3 that had the switch(es) mounted on the pedal cover, under the bonnet.

Then there is the switch in the PDWA,

brake_warning_light1.jpg

Also the switch monitoring the vacuum in the brake servo.

vac_brake_switch.jpg

So, the original question makes sense.

Unfortunately I don't recall the thread, although I'm sure the question has come up several times on the Series 2 Club Forum.

Regards

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OK, I wasn't sure you were still interested, having found a solution elsewhere.

My instinct says it could well be the same thread as the pipe nuts, so 3/8" UNF springs to mind, that is 24 TPI (Threads Per Inch).

Do you have a screw of this size to try?

The original part number was 560775, which many sites, Craddocks & LR Series are examples, say STC1689 is the replacment, but LR Series says this is 1/8 NPT x 27 TPI thread. (NPT is National Pipe Taper). I'm doubtful, as this is an American thread sizing. It might fit a more modern version of the five way junction, but not an original example, which I'm going to guess you have.

I'm reading your last post as saying you have found this out already, so I've included the 'misdirection' here merely for completeness.

The Dingocroft page makes interesting reading, especially as they have a well earned reputaion for being helpful, that is you can talk to someone over the phone and he will actually use his brain to help you out.

Scroll down the page and you will see they stock replacement 5 way unions, but also say quite clearly that while the 3/8" UNF threaded switch they sell will fit this 'new' union, the same switch will not fit an original union. (3/8" UNF has an OD of 0.375" and 24 TPI).

For original 5 way unions they offer the same STC 1689 part number as the others, but say the thread is 1/8" BSP, which I'm prepared to believe is the original thread. (1/8" BSP has an OD of 0.383", and is 28 TPI)

All these parts are on the same page I have linked to, although the connectors have changed from screw clamps to Lucar tabs, which may be something you will have to put up with.

If you don't have a known spare 3/8" UNF screw to try in the union, do you have a fine enough steel ruler (plus a steady hand and good eye) to count the threads on the 1/4" of a current switch?

Obviously, 24 TPI = 6 threads in a quarter inch, while 28 TPI =7 threads in a quarter inch, while a NPT 27 TPI will be just under 7 threads in a quarter inch.

I'm hoping you can do the thread checks today, to prepare you for a slightly more informed discussion with Dingocroft on Monday.

We will be interested to hear what the successful outcome is :-)

Regards.

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I too love this forum, great detailed reply David!

Another thumbs up for Dingocroft but I am lucky enough to live near them, a great indipendant supplier these are getting fewer and need supporting.

Marc

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