'40 brake lamp switch / master cylinder issue?

[Kube]

Okay guys, I'm getting frustrated.
Working on a '40, stock brakes.
Wiring is all good for certain.
I can get the tail lamps to light up IF I jump the two wires at the brake lamp switch.
I have power on one wire as I should have.
I have replaced the switch three times. Two nos switches and one brand new replacement.
As you guys know, when applying the brake pedal, the hydraulic force should close the switch circuit and the brake lamps should light up. Testing, there should be power to both terminals at the switch.
They don't. Not with any of the switches.
So, my way of thinking is the hydraulic pressure is not activating the switch(s).
Car stops just fine and has decent pedal.

Oh, if I jump the two leads at the switch, the brake lamps are nice and bright.
What the heck am I missing?

[tubman]

An obstruction in the master cylinder port?

[Kube]

Originally Posted by tubman

An obstruction in the master cylinder port?

That's my thinking Denny. If I pull the switch with the pedal engaged, I do get fluid to come out of the rear of the cylinder. So, at least I know it is not fully obstructed.

[Mart]

Mike, unless I'm missing something, it can only be 3 duff switches. If you bypass the switch, the brake lights work. Do you have a known good switch on another vehicle? Try fitting that just to prove the point.

Is the switch fitted to the normal 40 type banjo bolt? If so there is no way it can not be seeing pressure if the brakes are working. Is the banjo bolt new of previously used? Is it drilled correctly?

If you loosen the switch slightly and pump the pedal, does fluid leak past?

[deuce_roadster]

I would swap out the MC. Maybe the fluid you see coming out the back isn't sufficient pressure to cause the switch to operate.
I would also try to operate the switch with air pressure and see if the lights come on.

[Kube]

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I did order a new master cylinder from Napa earlier today. I have had good luck with those in the past.
The brake lamps did work a few weeks ago albeit only for a short time. A person following the car had said the lights seemed to "fade" away.

Mart, all authentic brake parts. I agree with you that three switches could be bad. However, at this point, I'm attempting to avoid any more frustration than necessary. The new master is only about $75.
I'll do my best to install it Thursday and will report back.

Gee, and I thought I'd seen it all

[petehoovie]

Silicone brake fluid? You need a low-pressure brake light switch for DOT 5 silicone fluid compatibility...


https://www.summitracing.com/parts/rfw-sw32

[tubman]

Originally Posted by petehoovie

Silicone brake fluid? You need a low-pressure brake light switch for DOT 5 silicone fluid compatibility...


https://www.summitracing.com/parts/rfw-sw32

To quote an old baseball saying : "Say it ain't so, Kube.".

[V8COOPMAN]

Originally Posted by petehoovie

Silicone brake fluid? You need a low-pressure brake light switch for DOT 5 silicone fluid compatibility...

Kube never even hinted at SILICONE brake fluid! Where the heck did that come from?

Coop


.

[Terry,OH]

bad stop light switches. Check them out on your air compressor using an ohmmeter. Should have very good continuity approaching zero ohms.

[slowforty]

On my 40 I had no Brake lights. Test light showed power to the Switch. Still did not work. Dug out a Good Meter, Only 3 volts going to switch. (?) Not enough power to light Brake lights. Still do not know why. Ran a new wire to the Switch with full 6 volts. Brake light work now.

[Kube]

Originally Posted by slowforty

On my 40 I had no Brake lights. Test light showed power to the Switch. Still did not work. Dug out a Good Meter, Only 3 volts going to switch. (?) Not enough power to light Brake lights. Still do not know why. Ran a new wire to the Switch with full 6 volts. Brake light work now.

If I cross the terminals at the switch, both lamps are very bright.

[TJ]

Is there a turn signal switch involved in the circuit?

[Kube]

Originally Posted by TJ

Is there a turn signal switch involved in the circuit?

Yes. However, they have worked for quite some time. And to reiterate, I have power TO the switch, just not on the opposite side of the switch.

[19Fordy]

I have never taken a master cylinder switch apart but, is it possible there is an internal failure of some type? I am using a Harley Davidson brake light switch with no problems. Brake fluid is silicone.
Here's some reading about the HD brake light switch that might help.
https://www.fordbarn.com/forum/showt...k+light+switch

This is crazy idea but, could it be the brake fluid?

[Kube]

Originally Posted by 19Fordy

I have never taken a master cylinder switch apart but, is it possible there is an internal failure of some type? I am using a Harley Davidson brake light switch with no problems. Brake fluid is silicone.
Here's some reading about the HD brake light switch that might help.
https://www.fordbarn.com/forum/showt...k+light+switch

This is crazy idea but, could it be the brake fluid?

I won't be able to swap the cylinder until tomorrow. My fingers are crossed that I am on the right path to a proper repair. I promise to let you guys know the outcome.

[STEVE O]

Hi Kube,
Just my opinion, but there is no way that the master cylinder is bad if it has enough pressure to stop the car ( which is by far more pressure) than it is required to activate the stop light switch. There has to be a blockage / restriction in the fitting or bad switches. Just my 2 cents. Steve

[40larry]

Originally Posted by Kube

I won't be able to swap the cylinder until tomorrow. My fingers are crossed that I am on the right path to a proper repair. I promise to let you guys know the outcome.

Mike
Did you connect an air pressure gauge to rear of mas cyl and check pressure

when pedal is held down?
Larry

[Kube]

Originally Posted by 40larry

Mike
Did you connect an air pressure gauge to rear of mas cyl and check pressure

when pedal is held down?
Larry

No, I did not. A grand idea indeed but I didn't think of that.

[Kube]

Originally Posted by STEVE O

Hi Kube,
Just my opinion, but there is no way that the master cylinder is bad if it has enough pressure to stop the car ( which is by far more pressure) than it is required to activate the stop light switch. There has to be a blockage / restriction in the fitting or bad switches. Just my 2 cents. Steve

Tonight, or most likely tomorrow, will tell the story

[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.

[kirkf]

Thanks!

Kirk

[mike42]

I’m encountering the same problem and was wondering who sells the better switch than NAPA ?

THX

[Kube]

Originally Posted by mike42

I’m encountering the same problem and was wondering who sells the better switch than NAPA ?

THX

Mike, see post #25. If you want me to search the exact switch product number, let me know.

[mike42]

Okay thx

[mike42]

Kube what store did you buy it from. I’ve heard not so good things on Napa and I think the new one I bought is no good too. Thx…..

[Ggmac]

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Just a test idea . If the swith is npt cant we just hook it to a grease gun and pump a very little . Or make a zerk fitting to the correct brake light switch thread . I know you’d have to rinse out the grease but it would identify a bad or good switch . If bad , no need to clean out the old grease .

[Kube]

Originally Posted by mike42

Kube what store did you buy it from. I’ve heard not so good things on Napa and I think the new one I bought is no good too. Thx…..

Like you, two from Napa that were poopy.

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

[Charlie Stephens]

Originally Posted by V8COOPMAN

Kube never even hinted at SILICONE brake fluid! Where the heck did that come from?

Coop


.

Silicone brake fluid goes through switches fast and going through 3 switches makes it a logical possibility. It is the first thing I thought of and I would have posted it but someone else already had.

Charlie Stephens

[Kube]

Originally Posted by Charlie Stephens

Silicone brake fluid goes through switches fast and going through 3 switches makes it a logical possibility. It is the first thing I thought of and I would have posted it but someone else already had.

Charlie Stephens

Charlie, going through three new brake switches in the course of three days? Not likely even if silicone fluid were involved.
Nope, just bad switches right out of the boxes.

[Mart]

I noticed that ford cortina about 1967 uses a 1/8 npt switch. Rockauto carry them. They have spade terminals rather than round but might represent something worth trying. One brand has a hex body which might represent a different manufacturer than the heavily pressed body of the replacement early ford type switches. I have had some failures too and have adapted mech switches.

[pistonbroke]

I with you Mart. I hate to crossbreed stuff as some of you know, but the mechanical switch that GM used on all the old five window (47 - 54) pickups works very well on my 41 pickup under the floor and out of sight for the most part. Having bright good working is a huge safety factor so this seemed acceptable to me as I drive mine every chance I get. The added bonus is you can flash your brake lights without actually applying the brakes. Tim

[aussie merc]

guys over here are changing to the switch from Harley Davidson they arnt cheap but they work