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Author: Subject: Brake Light Pressure Switch
bassett

posted on 21/6/14 at 08:59 PM Reply With Quote
Brake Light Pressure Switch

Hi, our brake lights only come on when you really stamp on the pedal, any ideas why this might be or could it be that we just need a lower pressure sensing switch? Anyone know what the thread is on the typical universal ones MNR sell - guessing 1/8npt but would be nice to confirm first.
Thanks
Adam





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SteveWallace

posted on 21/6/14 at 09:10 PM Reply With Quote
It could be that you have a small air bubble between the hydraulic fluid and the sensor. Try loosening it a bit and get someone to press the brake peddle to bleed it whilst you tighten it again. It worked for me.

Of course, if what you have is a micro switch behind the brake peddle then I'm talking rubbish.

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bi22le

posted on 21/6/14 at 09:11 PM Reply With Quote
Im on my phone atm so cant help. But do a search for my posts including the words brake switch.

You will get a vw (I think) part number for a brake switch. its is lower pressure sensing. Buy it from ebay.

I had the same problem and this solved it, for less than a tenner.





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big-vee-twin

posted on 21/6/14 at 09:12 PM Reply With Quote
Usual problem is they are mounted upside down and trap air inside





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bassett

posted on 21/6/14 at 09:26 PM Reply With Quote
Sorry should have been a bit more specific - its mounted on the front hydraulic line at the 4 way piece that splits for the left/right calipers. It is mounted at the top of junction.

Steve- thanks will give it a quick bleed to check for air although i had suspected it wasnt this given the brakes are solid even under heavy use but cant hurt to try again.

Bi22le - thanks i will look that up

Adam





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bassett

posted on 21/6/14 at 09:52 PM Reply With Quote
something like this?
Brake Light Switch VW GOLF 1.8 82-92





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ashg

posted on 21/6/14 at 10:24 PM Reply With Quote
you have it the wrong way up the wires should be facing towards the floor not up to the bonnet.





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bassett

posted on 21/6/14 at 10:32 PM Reply With Quote
Damn, wish the manual had mentioned that as its a pain in the arse job now. Thinking about it though yes that could easily be trapping some air! but might try that other sensor at the same time if it is more sensitive and if that still doesnt work will have to turn it upside down.





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coozer

posted on 21/6/14 at 11:01 PM Reply With Quote
I had the same problem on my MNR, I moved it from the top to the side, put the brake line from the cylinder into the top.

Some peeps have filled the switch with red grease to get rid or the air bubble.





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owelly

posted on 21/6/14 at 11:09 PM Reply With Quote
I'm bemused. How would the air bubble stop the switch from activating? Pressure is pressure no matter what is transferring it. If the brake line has enough pressure to hold the pedal off the discs (if you see what I mean), then that same pressure will be the same for the entire piped area.





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Ben_Copeland

posted on 22/6/14 at 06:35 AM Reply With Quote
Same way as you get spongy brakes when you have air in the system. Air doesn't compress like brake fluid.





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britishtrident

posted on 22/6/14 at 07:40 AM Reply With Quote
Pressure is pressure nothing to do with air bubbles.
The cause of the problem is two fold the brake system on a Seven style car has a much lower working pressure than modern heavier vehicles and the switches that are available these days are crap compared to the old Lucas switches.





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daviep

posted on 22/6/14 at 08:35 AM Reply With Quote
quote:
Originally posted by Ben_Copeland
Same way as you get spongy brakes when you have air in the system. Air doesn't compress like brake fluid.


Yeah but OP says the pedal is solid.

Cheers
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owelly

posted on 22/6/14 at 09:09 AM Reply With Quote
And the spongy brakes caused by air would make the pressure in the whole system less, not just at one point.





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loggyboy

posted on 22/6/14 at 11:00 AM Reply With Quote
The op says it does work, just needs lots of pressure, if air is trapped it could be small enough to not notice on braking, but enough to isolate the sensor until the pressure builds.





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britishtrident

posted on 22/6/14 at 04:08 PM Reply With Quote
quote:
Originally posted by loggyboy
The op says it does work, just needs lots of pressure, if air is trapped it could be small enough to not notice on braking, but enough to isolate the sensor until the pressure builds.


That would re-write the laws of physics, pressure of working fluid ( ie gas, vapour or liquid) in vessel is exerted equally.





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Johneturbo

posted on 13/10/14 at 06:13 PM Reply With Quote
Did you ever solve this Adam?, mine was rather bad many a person would say my brake lights wern't working, i recently bought a new switch and it was better but still doesn't come on with light braking as you know driving a bec there is a lot of engine braking.

mine is the same orientation as yours with the switch on top of the 4way.

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bassett

posted on 17/1/15 at 03:26 PM Reply With Quote
Been a while but now decided to do quite a few over due jobs whilst we look into something major. The brake light switch is one of them so will let you know how it goes.

First major job is to get the engine out and have the gearbox looked at/rebuilt as it has been momentarily popping out of gear when accelerating in 2nd gear shortly after youve changed into 2nd. Hopefully have this and all the other jobs sorted by mid Feb as im sure the engine will be off for a week or two i just hope its nothing too expensive!

Adam





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beaver34

posted on 17/1/15 at 07:17 PM Reply With Quote
I had this issue, I did away with it and just fitted a switch infront of the brake pedal a micro switch from maplin
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bassett

posted on 29/4/15 at 08:27 PM Reply With Quote
Johneturbo - yes we did solve this, one of the only positives from having the winter rebuild.

In terms of what we did i bought a new brake switch from ECP, we moved the switch from the top to middle/centre of the 4 way t piece. Was a bit of a struggle to move the brake pipe to the top but managed in the end. First test and you barely need to lean on the pedal now which should be a lot safer on the road. We didnt use any grease just a slight fill of fluid before we tightened it up.

Thanks for the advice everyone

Adam





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