'40 brake lamp switch / master cylinder issue?

[slowforty]

Did you try wiring a temporary mechanical switch to see what happens. But if you say the lights work if you connect the teminals. I think it is a switch issue. I use the regular stop light switches, I can get 4 for the price if a H-D one and they work just as well.

[big job]

What am "I" missing. Seems every year a new brake switch. This month got one from O'rielys instead of Napa./ not to mention bad condensers and other irritating new parts. as a side note I have been watching mass production in China and I am impressed with factory's hospital clean conditions and space age measuring that makes micrometers a thing of the past. interesting.

[aussie merc]

i gave up on hyd switches after 3 failures in 2 weeks went mechanical no problems 5 years and counting

[38 coupe]

I suspect three bad switches, and will be very interested in what the final investigation reports.
I purchased ten new pressure switches about four years ago. My 53 seems to have a switch fail about every two years. I'm not willing to cut into my new wiring to install a mechanical switch when the pressure switch is so easy for me to replace (Ford put the whole mess under the hood starting in 1952, way easier to work on than 1940 through 1951). Between replacing switches on my car and helping other people with failed switches on tours I am down to three spare switches.

[Kube]

A follow up is due to all the nice folks that had offered me advice. This one had really frustrated me.
Turned out to be a couple of issues that kinda "muddied the waters".
Master cylinder was dirty as was the entire hydraulic system. So, I believe it was a good thing that this issue showed up. I flushed the entire system and replaced the master with a new unit from Napa. I have had very good luck with these. As a plus, the casting and cap are concourse correct for 1940.
Then there's the switches. Four bad in a row. ARGGHH! Are you kidding me?
Three NOS, concourse correct switches and a new one from Napa. The fifth one purchased off of Amazon for $10 worked like a charm.

So, thanks guys for the advice and your patience with me.

[19Fordy]

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WOW! Four bad switches in a row.
That's a sad commentary on the quality of today's replacement parts. Glad you solved the problem.

[tubman]

When I restored my '51 in 1987, I removed the original switch, cleaned it up and re-installed it in the rebuilt master cylinder. Not a problem since. I have never had a bad original switch in almost 70 years, so I'm saving them.

[Kube]

Originally Posted by tubman

When I restored my '51 in 1987, I removed the original switch, cleaned it up and re-installed it in the rebuilt master cylinder. Not a problem since. I have never had a bad original switch in almost 70 years, so I'm saving them.

How did you clean it up?

[19Fordy]

QUESTION: I would think that to "clean up" the switch you would have to take it apart.
Then the problem becomes reassembling it and sealing it so it doesn't leak under pressure. As I recall there is a small diaphragm inside the unit that flexes under pressure to "make and break" the flow of electricity to the tailights.

[51woodie]

I had a problem with the switch on my ‘46 Coupe, bought one from the Harley dealer, and no problem since. Not concours, but it works.

[tubman]

Originally Posted by Kube

How did you clean it up?

Actually, I just used some solvent on a rag to wipe the dirt and oil off the exterior. I was only concerned with cosmetics because it had always worked.

[Kube]

Originally Posted by tubman

Actually, I just used some solvent on a rag to wipe the dirt and oil off the exterior. I was only concerned with cosmetics because it had always worked.

Poopy. I was hoping you had figured out a positive method of cleaning the interior.
NOS (concourse correct) switches are rare. I'd sure like to figure out a method.
One trusted fellow here on the Barn suggested cycling the switch numerous times. I'll try that and see what happens.

[Mart]

Mike, all, would it be an idea to rig up some sort of device to test the switches? An old but serviceable master cylinder, a lever and a couple of fittings might allow at least a heads up of a bad switch. Someone suggested using air.. is that feasible? What psi is needed to make the contact in a good switch?
I must admit, I fitted a mech switch in my sedan after a couple of failed hyd switches. My pickup still has it's original hyd switch and still works.

[Kube]

Originally Posted by Mart

Mike, all, would it be an idea to rig up some sort of device to test the switches? An old but serviceable master cylinder, a lever and a couple of fittings might allow at least a heads up of a bad switch. Someone suggested using air.. is that feasible? What psi is needed to make the contact in a good switch?
I must admit, I fitted a mech switch in my sedan after a couple of failed hyd switches. My pickup still has it's original hyd switch and still works.

Mart, I did rig up an air pressurized testing system. I set the pressure at 23#. I was advised that may be quite low.

[19Fordy]

I hope a Fordbarner will carefully take apart a "bad" switch and examine it to ascertain what actually causes the switch to fail.
I thinks it's because the mechanical seal between the internal contacts eventually leaks preventing proper electrical continuity.

[STEVE O]

A quick google search shows Ron Francis makes a low psi one for 20-50 psi, where as a normal stock 60-120 psi. Of course we know the pressures to apply wheel cylinders can go upwards of 1000 to 2000 psi for harder braking.
Steve

[Kube]

Originally Posted by STEVE O

A quick google search shows Ron Francis makes a low psi one for 20-50 psi, where as a normal stock 60-120 psi. Of course we know the pressures to apply wheel cylinders can go upwards of 1000 to 2000 psi for harder braking.
Steve

That's very helpful Steve. Thank you!

[STEVE O]

Your welcome. I also read normal braking psi is 300-500 psi where as 600 psi and above is considered panic braking. Glad you got your lights working as its nothing any more frustrating than something like that.
Steve

[kirkf]

Originally Posted by Kube

I flushed the entire system and replaced the master with a new unit from Napa. I have had very good luck with these. As a plus, the casting and cap are concourse correct for 1940.
Then there's the switches. Four bad in a row. ARGGHH! Are you kidding me?
Three NOS, concourse correct switches and a new one from Napa..

Do you happen to remember the NAPA part number for the master cylinder, and which Amazon switch you went with?


Kirk

[Kube]

Originally Posted by kirkf

Do you happen to remember the NAPA part number for the master cylinder, and which Amazon switch you went with?


Kirk

Amazon:
WQSING Hydraulic Rear Brake Light Switch DS-272191 Compatible with Harley Davidson Sportster Softail Touring Dyna Super Electra Glide Road King FXR Deluxe Fat Boy Low Rider Heritage 72023-51A
Napa:
Part #: NMC M1050, with my discount, about $70. This is a brand new unit.