Rear Brake Light Pressure Switches

What pressure should it switch at and which is suitable for DOT 5 fluid?

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Mongrel505558
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Rear Brake Light Pressure Switches

#1

Post by Mongrel505558 »

Need to replace the brake light pressure switch on my rear disk brake line. I quick search of the web takes me to a lot of switches available from Auto Zone, O'Rielly Auto Parts, Advanced Auto Parts, J&P Cycle, etc. The ones from the auto parts stores are mostly listed as having a switching range of 60 to 120 psi. The J&P offerings don't list that in formation. The one thing I find in common is they aren't compatible with silicone based fluids. My brakes use DOT 5. I assume that Shovelhead rear brakelight switches are suitable for use with DOT 5 since that's what the brakes were designed to use. Whatever I end up with has to have a 1/8 NPT male fitting on it. I never really considered what the switch point should be and what pressure range is typically exerted by a rear brake master cylinder (5/8").



RooDog
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Re: Rear Brake Light Pressure Switches

#2

Post by RooDog »

You are only going to exert as much pressure as the brake requires at the time of usage regardless of the MC size. I use GMA 5/8 MCs on my scooters, and an automotive switch, 1/8 NPT with which ever terminal style is best at the time, either flat push-on spade, or screw post terminals. 1974 VW Super Beetle switch comes to mind. I believe brake fluid compatibility, much like vale seats fuel types, is just plain BS. Dot 5 is not harmful to much of anything.
....RooDog....

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Re: Rear Brake Light Pressure Switches

#3

Post by Mongrel505558 »

RooDog wrote:
Fri Jun 26, 2020 5:21 pm
You are only going to exert as much pressure as the brake requires at the time of usage regardless of the MC size. I use GMA 5/8 MCs on my scooters, and an automotive switch, 1/8 NPT with which ever terminal style is best at the time, either flat push-on spade, or screw post terminals. 1974 VW Super Beetle switch comes to mind. I believe brake fluid compatibility, much like vale seats fuel types, is just plain BS. Dot 5 is not harmful to much of anything.
....RooDog....
If that's the case then I might as well buy a $12 switch from Auto Zone. The one I had on there before was from Drag Specialties, I think, and it didn't last very long.

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Re: Rear Brake Light Pressure Switches

#4

Post by RooDog »

Exactly.
Brake light switches are not a high tech item.....Just be sure to install it so that it is easy to replace when the time comes.....

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Re: Rear Brake Light Pressure Switches

#5

Post by Mongrel505558 »

RooDog wrote:
Sat Jun 27, 2020 5:01 am
Exactly.
Brake light switches are not a high tech item.....Just be sure to install it so that it is easy to replace when the time comes.....
It's on the transmission mounting plate aft of the kicker side. Tee bracket shares that plate mounting bolt. Relatively easy access. I don't have to take anything off to get to it. Just have to refill/bleed brake after swap and clean up.

Speaking of transmission...mine went south yesterday. I've been test riding close to home to try to get rid of an off-idle flat spot. Pulled in the clutch and got a grinding sound and a wail like a wounded elephant or something. Clutch cable went slack and bike lost propulsion. I shut down and pushed about 50 yards to home. Luckily nothing locked up, even though I was going slow, and I could get into neutral so the bike would roll. Now the mainshaft moves with the clutch pushrod out about a half-inch when I pull in the clutch lever and I can manually push it right back in. I haven't taken anything apart yet, but my best guess, for what it's worth, is the big mainshaft bearing behind the kicker gear blew apart. As far as I know that's the only thing, along with a nut and the kicker gear and nut, that holds the mainshaft from running out. This would be a story for a different post, but I've been asking so many questions as I tackle just about every aspect of this bike that I don't want to become a PITA. For these bikes, though, there's no better source of knowledge I've found so far that's readily available.

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Re: Rear Brake Light Pressure Switches

#6

Post by Larry »

I've never had luck with DOT 5 and pressure switches. I've always had to convert to a mechanical switch. Disassembly of pressure switches showed fluid at the contacts. Apparently DOT 5 will find leaks that DOT 3 will ignore.

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Re: Rear Brake Light Pressure Switches

#7

Post by RooDog »

I currently have a 1970s OEM, Harley, FX mechanical Stop lamp Switch listed on eBay:

eBay item number:143014673683

https://www.ebay.com/itm/143014673683?s ... 1555.l2649

It mounts so that when your foot pressure is off the pedal and the pedal retracted, at rest, the plunger is pushed in, off, and when you apply the brake, the pressure is released and an internal spring pushes the plunger out, thus switching the light on. No linkage was required in an OEM installation. Too complicated for me with FX & FL ST foot controls, so I use the automotive hydraulic switches mounted in a T block behind the transmission, hard line coming in from the front, and the flex line to the caliper out the rear. Simple, effective, inexpensive, and much easier than reading through my ramblings here this morning....
...RooDog...

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Re: Rear Brake Light Pressure Switches

#8

Post by Mongrel505558 »

RooDog wrote:
Sat Jun 27, 2020 1:45 pm
I currently have a 1970s OEM, Harley, FX mechanical Stop lamp Switch listed on eBay:

eBay item number:143014673683

https://www.ebay.com/itm/143014673683?s ... 1555.l2649

It mounts so that when your foot pressure is off the pedal and the pedal retracted, at rest, the plunger is pushed in, off, and when you apply the brake, the pressure is released and an internal spring pushes the plunger out, thus switching the light on. No linkage was required in an OEM installation. Too complicated for me with FX & FL ST foot controls, so I use the automotive hydraulic switches mounted in a T block behind the transmission, hard line coming in from the front, and the flex line to the caliper out the rear. Simple, effective, inexpensive, and much easier than reading through my ramblings here this morning....
...RooDog...
I pulled my transmission this morning and dropped it off at a shop that I trust. There's a NAPA next door to it so I stopped in to see if I could get a brake light switch. I got the typical response when I couldn't give the kid a make, model and year of a specific car. He couldn't be bothered. I tried 74 VW like you mentioned and he said I'd have to go to an import car parts store. I said all I need is a pressure switch with a 1/8" NPT male connection and two electrical terminals or wire leads. He didn't seem to know what I was talking about, so I thanked him for his time and left. I'll try another place this afternoon where I might find a more knowledgeable counter person, or maybe someone born before the 74 Super Beetle. Usually have better luck at the mom and pop shops than the franchise chain stores. Too bad around here the mom and pop places are getting harder to find.

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Re: Rear Brake Light Pressure Switches

#9

Post by RooDog »

Here are three NAPA Stoplight Switches. The last one is probly what you want, and it's only $13.49.....
Best to give the Millenium at the parts store a number, so he don't have to put any effort into doing his job....

https://www.napaonline.com/en/p/MPESL11 ... ght+switch

https://www.napaonline.com/en/p/MPESL13 ... ght+switch

https://www.napaonline.com/en/p/MPESL14 ... ght+switch

....RooDog....

Mongrel505558
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Re: Rear Brake Light Pressure Switches

#10

Post by Mongrel505558 »

RooDog wrote:
Sat Jun 27, 2020 6:20 pm
Here are three NAPA Stoplight Switches. The last one is probly what you want, and it's only $13.49.....
Best to give the Millenium at the parts store a number, so he don't have to put any effort into doing his job....

https://www.napaonline.com/en/p/MPESL11 ... ght+switch

https://www.napaonline.com/en/p/MPESL13 ... ght+switch

https://www.napaonline.com/en/p/MPESL14 ... ght+switch

....RooDog....
I'll probably buy the first one you listed with the screw terminals online and then pick it up at the store later this afternoon. Seems like that'll save time and confusion at the counter.

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