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Rootes75
Joined: 30 Apr 2013 Posts: 3816 Location: The Somerset Levels
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Posted: Mon Nov 19, 2018 11:23 am Post subject: Hydraulic Brake Light Switch |
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I have connected up my hydraulic brake switch on my Commer lorry and I get no life from it at all.
I know fluid is passing into it and it isn't blocked and the wiring is new and to a terminal that I know is live.
Is there anyway to check the switch, or looking round on ebay is it just easier to replace it? _________________ Various Rootes Vehicles. |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4105 Location: South Cheshire
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Posted: Mon Nov 19, 2018 8:14 pm Post subject: |
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There have been lots of issues with some brands of this switch, when my dad had his MM he had about 6 that failed either straight out of the box, or within a few months. It was so bad that he rigged up an additional dashboard warning lamp wired to the brake lamps
To check the switch simply measure the resistance when the system is pressured.
Dave |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4105 Location: South Cheshire
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Posted: Mon Nov 19, 2018 8:19 pm Post subject: |
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There have been lots of issues with some brands of this switch, when my dad had his MM he had about 6 that failed either straight out of the box, or within a few months. It was so bad that he rigged up an additional dashboard warning lamp wired to the brake lamps
Dave |
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jp928
Joined: 07 Jun 2016 Posts: 249 Location: Australia
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Posted: Wed Nov 21, 2018 4:11 am Post subject: |
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One car I had many years ago had an indicator for working brake lights - round can like a flasher, connected to brake circuit; mounted in a plastic case that screwed to bottom edge of dash, lit a bulb behind a plate saying 'Brakes', accompanied by an audible click. These days you would run a lead from switch output to a 12v LED (via a resistor) mounted in some sort of bezel.
jp 26 Rover 9 |
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Phil - Nottingham
Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham
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Posted: Wed Nov 21, 2018 11:32 pm Post subject: |
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I have one of those accessory warning lights on 3 of our classics as it warns of a single bulb failure.
The hydraulic switches can be very insensitive and only work when brakes are full on when they age and new ones are very inconsistent and can even leak after a short time _________________ Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2 |
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lowdrag
Joined: 10 Apr 2009 Posts: 1585 Location: Le Mans
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Posted: Thu Nov 22, 2018 2:12 pm Post subject: |
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I've no idea if you have managed to repair your switch, but I always carry a spare like this in my E-type. Not dear, and I've replaced only two over 30 years.
https://www.sngbarratt.com/uk/#!/English/parts/9814f8c3-58d9-4a86-a60b-401be3902ece
https://www.sngbarratt.com/uk/#!/English(US)/parts/74c68473-49f8-481d-b474-c1ab92e15360
Hope this helps. |
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Peter_L
Joined: 10 Apr 2008 Posts: 2680 Location: New Brunswick. Canada.
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Posted: Thu Nov 22, 2018 2:47 pm Post subject: |
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I never had a problem with any that I had, but years back I remember a mechanic saying that depending on location it is possible for an air bubble to get trapped and stay there. I guess it's possible, but in theory seems more likely than in practice. Opinions welcome because this idea was floated to me over 50 years ago. |
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Phil - Nottingham
Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham
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Posted: Thu Nov 22, 2018 6:55 pm Post subject: |
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I have that and it could well be true but loosening a failing switch and pressing the pedal down to eject some fluid, I had only last week had no effect. A old battered one I put in worked as good as a mechanical switch _________________ Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2 |
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Rootes75
Joined: 30 Apr 2013 Posts: 3816 Location: The Somerset Levels
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Posted: Thu Nov 22, 2018 8:53 pm Post subject: |
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Thats strange with SNG comment, looking through the original parts list the lockheed switch is also used on Jaguars. _________________ Various Rootes Vehicles. |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4105 Location: South Cheshire
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Posted: Fri Nov 23, 2018 11:27 am Post subject: |
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In reality the only difference between the switches will be the thread size; they all should operate from around 50PSI (light braking) to over 2000PSI. And be capable of switching the current a couple of brake bulbs draw.
The symptoms that I saw with modern reproduction Lucas switches were either requiring a very high pressure to operate or failed "OC" The only failure I ever had with an original switch was a "SC" fail....possibly although the modern and original switches look the same externally, they are engineered differently internally?
peterwpg wrote: | I never had a problem with any that I had, but years back I remember a mechanic saying that depending on location it is possible for an air bubble to get trapped and stay there. I guess it's possible, but in theory seems more likely than in practice. Opinions welcome because this idea was floated to me over 50 years ago. | A bubble in the system can't affect local system pressure, and said pressure has to be the same on both "sides" of the bubble.
Dave |
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