Brake light switch 4-way union

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Roger King
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Brake light switch 4-way union

Post by Roger King » Sun Jul 16, 2017 9:00 am

I've just noted a change to the Wiki on brake light switch unions. I don't know anything about MGBs or their parts, but this entry tells me that the MGB brake light switch has a 1/8" NPT thread, unlike the correct Cobra one. I would dearly like to use this thread size for the brake light switch, but can't find a brass union that will take both the switch (1/8" NPT) and three pipe unions. Is this an MGB part? The only MGB ones I can find take the switch plus four pipes - I'm hoping someone more au fait with 'B's can tell me there's a union for the switch and 3 pipes only.

The reason for this is that I'm completely fed up with the crap Lucas repro brake light switches. Generally they don't come on until you are properly standing on the pedal, and most cause a high-speed flickering when initially applied (I noticed a lot of cars were doing this on the run out from the Chairman's BBQ). They are of very varying quality and often don't like LEDs with their lower current draw.
Having nearly been rear-ended in my Cooper S last year because of this problem, I discovered via the Mini Cooper Register that a Harley Davidson switch is also 1/8" NPT (as is the Mini), and as they are made by Accel they are very reliable and come on at the lightest touch of the pedal. I duly fitted one and the Min's brake lights are now excellent and reliable. I'd really like to fit one to the Cobra, but at the moment this looks like I'll need to use the 4-way union and blank one off.
Any 3-ways (plus switch) out there, chaps?

Roger

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clive
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Re: Brake light switch 4-way union

Post by clive » Sun Jul 16, 2017 12:28 pm

Hi Roger,

Probably a man of your vast knowledge already knows, but have you tried BGC Motoorsports?
http://www.bgcmotorsport.co.uk/

CJ
Cheers, Clive.

(If I'm not here I'm in my workshop or on the golf course!)

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Re: Brake light switch 4-way union

Post by peterc » Sun Jul 16, 2017 12:37 pm

Roger,
I am the person who added a note to the brake light switch being 3/8" UNF for a 4 way union supplied by BGC.
I had purchased an MGB version in the belief that it was correct but then found it was 1/8" NPT.
I then managed to purchase a Lucas part not a repro. I can advise you later on the supplier as I can access that info right now.
You maybe able to find a special fitting supplier to obtain a convert or from UNF to NPT.
Peter C

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Roger King
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Re: Brake light switch 4-way union

Post by Roger King » Sun Jul 16, 2017 3:00 pm

Yes, nothing showing at BGC.

Thanks for the info Peter, but the Lucas ones have always been pretty rubbish so I don't think NOS would help. I've had problems with them for the last 45 years on every British car I've had fitted with them...
The US one for the Harley is just better made and clearly has better switching internals, that's why I want to use it if I can rig up a 1/8" union. No, its' not original, but not easy to tell it apart and anyway, I don't want dodgy brake lights. I have followed too many cars fitted with these on classic runs over the years, some of which never showing brake lights even under obviously quite severe braking. The best answer would be a mechanical switch on the pedal but with the original pedal box that would not be easy and is a step too far for me anyway.

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Re: Brake light switch 4-way union

Post by frats289 » Wed Jul 26, 2017 5:21 pm

Roger

Mine is a 3 pipe union, I think it is the original one that came off the donor '72 MGBGT. It also looks very much like the one I've recently taken off the '58 Sprite I'm now renovating.

Frank

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Roger King
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Re: Brake light switch 4-way union

Post by Roger King » Wed Jul 26, 2017 6:01 pm

Thanks Frank - is it 3/8" UNF or 1/8" NPT for the switch? And when you say '3-union', do you mean 3 plus the switch?
Roger
Just discovered Automec will make what I need for £14.50 - thanks to Peter A for the suggestion

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Re: Brake light switch 4-way union

Post by peterc » Wed Jul 26, 2017 10:11 pm

Having just got the wife to check on the brake light illumination relative to my foot pressure I can unfortunately agree that the Lucas switch does not react until peddle is firmly pushed. So yes, you can brake lightly with no brake lights showing.
The BGC web site does show a 4 way union under brake line fittings ( after clicking on expand products) with options of UNF or Metric options. The problem is to track down an adapter to mount the BSP thread.
Peter C

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Re: Brake light switch 4-way union

Post by frats289 » Thu Jul 27, 2017 9:18 am

Don't know the thread I'm afraid Roger but it accepts the '72 style Lucas switch. Yes, 3 plus the switch.

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Re: Brake light switch 4-way union

Post by peterc » Sun Jul 30, 2017 7:39 am

Discussions at Silverstone where Clive suggested that maybe a small amount of air gets trapped next to the switch thus compressing the air delays the activation of the switch.
Just a thought.
Peter C

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Roger King
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Re: Brake light switch 4-way union

Post by Roger King » Sun Jul 30, 2017 9:04 am

peterc wrote:
Sun Jul 30, 2017 7:39 am
Discussions at Silverstone where Clive suggested that maybe a small amount of air gets trapped next to the switch thus compressing the air delays the activation of the switch.
Just a thought.
Peter C
Yes, I have been bleeding the switches with a hypodermic syringe every time I fit one for over 40 years now. I suppose air could move along the system later during the bleeding process and 'pop up' into the switch after fitting, but two things count against this: firstly, I have tried removing them after bleeding the system to re-prime with a syringe (you don't lose much fluid), and secondly it only happens with the Lucas switch, not the Accel one - which is of the same design and appearance but is obviously better made.

I've been in touch with Automec who do not make the 1/8" BSP switch + 3 pipe union as a standard item (so it's not MGB), but will make as a special for £14 a time. Well worth it to have brake lights that come on early (and hopefully are less prone to flickering, although I think that's an LED load problem - it doesn't happen in the same system fitted with filament bulbs), in my opinion.

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