Brake Light Shame.... - Page 2

Kauai1800 · Oct 20th, 2007, 01:03

Thanks so much Andrew!

Looks like you even took a picture just to show me.

The people on this forum are awesome....

Ron Kwas · Oct 20th, 2007, 16:49

Forum;

The pressure sensing hydraulic switches are just not reliable...the actual electrical contact area closes under slow-speed, low closing force...a perfect recipe for non-function from an engineering design standpoint... it's a poor situation...the pressure comes up very slowly during normal braking, and thus puts the switch diaphram through a linear (flexible) region which closes the contact quite slowly, typically not breaking through the carbonized surface (which occured when the contact was last carrying current and opened), when it should ideally snap closed, breaking through this non-conducting layer...add to that aging and relaxation of the diaphram, and most of the switches quit...some quite soon after installation...add to that the unavoidable delay factor of having to make pressure in the system in order to show brake lights, and all manufacturers including Volvo in about '67, changed over to mechanical switches.

Regarding the "sludge" one poster found in the switch...I just can't believe this explanation...IMO, "sludge" is not likely what keeps the switch contacts from closing...in the first place, "sludge" would certainly transfer the pressure to the contact diaphram just as easily as clean fluid (I guess that means that just as a fluid is non-compressible, so is "sludge")...further, no "sludge" is capale of withstanding the high pressure which occurs in the system. I believe the failure mechanism is as described above.

...bottom line IMO is to just upgrade to a mechanical pedal position sensing switch, loose all of the disadvantages, and get all of the advantages: Reliably Brake Light operation the instant the pedal leaves its rest position. You don't even need to bleed the system!...

Andrew; Please get back to me with your design if you would...I have another interested party for the RHD version and I could use the detailed design...

Greetings from a foliage colorful New England!

stuart131 · Oct 23rd, 2007, 20:38

You might have already sorted this, but assuming your car is an Amazon, just get a new brake switch, the one thats on a bracket in front of the brake pedal. About £10 from Brookhouse and even an incompetent like me managed to fit this in 10 mins.
Brake lights were restored immediately.

Ron Kwas · Dec 14th, 2007, 11:19

Forum;

For those interested in my detailed explanation of the chronic failure of these switches, I have just completed a new tech article, which I invite you to read: http://www.sw-em.com/hydraulic%20bra...es%20notes.htm

Cheers

Oct 20th, 2007, 01:03	#11
Kauai1800 Member Last Online: Aug 11th, 2019 22:13 Join Date: Oct 2007 Location: Island of Kauai	Thanks so much Andrew! Looks like you even took a picture just to show me. The people on this forum are awesome.... __________________ *"Relax in the safety of your own delusions."* - JR "Bob" Dobbs

Oct 20th, 2007, 16:49	#12
Ron Kwas Premier Member Last Online: Today 13:32 Join Date: Jul 2007 Location: Connecticut, USA	Hydraulic brake light switches vs. mechanical Forum; The pressure sensing hydraulic switches are just not reliable...the actual electrical contact area closes under slow-speed, low closing force...a perfect recipe for non-function from an engineering design standpoint... it's a poor situation...the pressure comes up very slowly during normal braking, and thus puts the switch diaphram through a linear (flexible) region which closes the contact quite slowly, typically not breaking through the carbonized surface (which occured when the contact was last carrying current and opened), when it should ideally snap closed, breaking through this non-conducting layer...add to that aging and relaxation of the diaphram, and most of the switches quit...some quite soon after installation...add to that the unavoidable delay factor of having to make pressure in the system in order to show brake lights, and all manufacturers including Volvo in about '67, changed over to mechanical switches. Regarding the "sludge" one poster found in the switch...I just can't believe this explanation...IMO, "sludge" is not likely what keeps the switch contacts from closing...in the first place, "sludge" would certainly transfer the pressure to the contact diaphram just as easily as clean fluid (I guess that means that just as a fluid is non-compressible, so is "sludge")...further, no "sludge" is capale of withstanding the high pressure which occurs in the system. I believe the failure mechanism is as described above. ...bottom line IMO is to just upgrade to a mechanical pedal position sensing switch, loose all of the disadvantages, and get all of the advantages: Reliably Brake Light operation the instant the pedal leaves its rest position. You don't even need to bleed the system!... Andrew; Please get back to me with your design if you would...I have another interested party for the RHD version and I could use the detailed design... Greetings from a foliage colorful New England!

Dec 14th, 2007, 11:19	#14
Ron Kwas Premier Member Last Online: Today 13:32 Join Date: Jul 2007 Location: Connecticut, USA	Failure of Hydraulic Brake Light Switches Forum; For those interested in my detailed explanation of the chronic failure of these switches, I have just completed a new tech article, which I invite you to read: http://www.sw-em.com/hydraulic%20bra...es%20notes.htm Cheers

Oct 23rd, 2007, 20:38	#13
stuart131 Senior Member Last Online: May 17th, 2022 10:30 Join Date: Dec 2003 Location: northampton	You might have already sorted this, but assuming your car is an Amazon, just get a new brake switch, the one thats on a bracket in front of the brake pedal. About £10 from Brookhouse and even an incompetent like me managed to fit this in 10 mins. Brake lights were restored immediately.

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