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bad brake pressure switches?


DJ194950
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https://ecihotrodbrakes.com/inline_brake_light_switch.htmlSaw this the other days for people who have been plagued with this problems as discussed a while back here.

 

Not Cheap but is a alternative.  FYI only -on my part

https://ecihotrodbrakes.com/inline_brake_light_switch.html

 

D

Edited by DJ194950
add address-corrected.
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I read the instructions, which states that if you have  a10 psi residual pressure valve then brakes to mount this switch upstream of the RPV.  IIRC, the RPV is built into the stock master cylinder.  Which I think means it is not useable in our stock setups.

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That would make this way harder ( and $$) o use in a 4 wheel stock system, but still do -able with a side line with a adjustable valve- BUT- way to much effort and- -

 

For those with updated  front discs  no biggie.

 

If I had read that info first I would have at least added this info.

 

Thanks for checking this and posting- Sniper, but you are the Sniper!  😃

 

DJ

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I have owned my 1939 Desoto with the stock brake light switch that screws into the brass line connector that is mounted to the frame in the engine compartment.  I have only chnaged this unit ounce in 35 years f owning the car.  The switch just works off og the hydraulic brake fluid to make the contact send the electrical current to the brake lights.

 

I can puchase the units fairly cheaply so why spend this extra money for such a simple switch that has been used for so many years.  Just reinventing the same switch again with this new unit.

 

Rich Hartung

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Just trying to help someone from having an issue.  The stock brake light switch is downstream of the RPV and it doesn't turn on until you step on the brakes.

 

I don't think I'll use any residual pressure valves on my disc brake swap.  Just to see how needed it is, or if it's another tribal knowledge story not applicable here.

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1 minute ago, desoto1939 said:

 

I can purchase the units fairly cheaply so why spend this extra money for such a simple switch that has been used for so many years. 

 

I think I can answer that, Ford uses a similar switch to sense brake pressure for the cruise control system.  They have been known to fail and since that CC circuit is always hot and not fused when brake fluid seeps into the electrical side it starts a fire and burns your vehicle and/or house down.  

 

I can understand someone being nervous about that. 

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If my brake light switch ever gives me problems I'm going to convert to a switch at the brake pedal that isn't dependent on hydraulic pressure. That will make it adjustable so I can set how much pedal travel it takes to activate the brake lights. Also will never have to worry about the switch developing a leak.

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I recall one time my brake lights stayed on a for a sec. Hmm. Caught my attention as I walked away from my parked car in the garage. Yet they went out 3 seconds later. Weird. Oh well. Carry on.

 

Couple weeks later I went out to start my car. Dead battery. Hmm. Weird. Maybe the light in the glove box is stuck on? Nope. Re-charge the battery & go for a drive. When I got back home notice a drain on the ammeter. I pulled out my clamp style multimeter/ammeter testing unit. With the key turned off, I tracked amp flow in the wires under the dash. Interesting. The wire leading right to the hydraulic pressure brake light switch. Remove wire at switch. Amp drain stopped. Bingo! Bought a generic modern replacement $10 pressure switch at a local parts store. Problem solved. I do like trouble shooting with an ammeter. 

Edited by keithb7
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1 hour ago, Sniper said:

 

I think I can answer that, Ford uses a similar switch to sense brake pressure for the cruise control system.  They have been known to fail and since that CC circuit is always hot and not fused when brake fluid seeps into the electrical side it starts a fire and burns your vehicle and/or house down.  

 

I can understand someone being nervous about that. 

Yep, I lost a very low mileage 2000 Expedition to that flaw.  Leaky switch along with a CC circuit that is always hot and unfused!, = disaster. 

 

I've replaced several of those over the years due to seepage and leaking air into the system. Especially true on Fords  Not my cars, customers.  

 

For that reason, and since I'm going to firewall mounted pedals, mine will get a simple mechanical switch activated by the pedal arm itself.

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Hydraulic brake switch failed more than once. 

Installed a mechanical switch on my 47 Desoto, under the floor. 

I cut a subpanel out of the large removable floor panel, to get at the brake switch and the bulb for the Jiffy Jet windshield washer.   

The photo shows the large panel removed and the subpanel in place. 

The mechanical switch has an arm riding on the brake pedal arm.  

 

608532696_floorpanel(7)flooraccesssub-panel2016.JPG.1353e256895ea3aecaa50fb790dbd121.JPG

 

 

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Posted (edited)

Source for the brake switch with the adjustable arm.??

 

I see them sold on some old Chevy parts sellers at To big of bucks I am sure.  So knowing a Mfg'er would save some $$.

 

TKS,

 

DJ

Edited by DJ194950
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Thanks for the reply, but I'd really like to find a part # and source with the adjustable 2 piece arm as your picture shows.

 

So much easier to mount and adjust.

 

DJ

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There was a Chrysler technical note in the early 1950's on this subject. I have it someplace.  Basically they knew they were having problems with the switch on the 6 volt cars. What they did was to create a new switch that was POLARITY SENSITIVE that addresses issue ---supposedly.

 

These can be identified by the fact that one of the two studs or mounting points is longer then the other.

 

I never have noted the difference in longevity. I always keep a spare in the car and a long socket with me just in case. If you are quick the fluid just runs out and no air gets in.

 

James

PS. On the '49 when I did the 4 wheel disc with the remote power brake booster I put the switch in there and can sit in the trunk and change it easy. It is also out of the dirt and heat of the engine bay. 

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Summit racing has at least 3 available. Different sellers but manufacturers?

 

From about $22 to $35 plus shipping. All seem to be direct form sellers..direct shipping. Costs?

 

Thanks for the  info!!  😀

 

DJ

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27 minutes ago, James_Douglas said:

There was a Chrysler technical note in the early 1950's on this subject. I have it someplace.  Basically they knew they were having problems with the switch on the 6 volt cars. What they did was to create a new switch that was POLARITY SENSITIVE that addresses issue ---supposedly.

 

These can be identified by the fact that one of the two studs or mounting points is longer then the other.

 

I never have noted the difference in longevity. I always keep a spare in the car and a long socket with me just in case. If you are quick the fluid just runs out and no air gets in.

 

James

PS. On the '49 when I did the 4 wheel disc with the remote power brake booster I put the switch in there and can sit in the trunk and change it easy. It is also out of the dirt and heat of the engine bay. 

So if the new switch that Chrysler came out with was polarity sensitive, is that to say that it matters which wire goes to a particular post/stud?

I thought the switch was just acting as an interruption of power going to the brake lights. 

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10 minutes ago, harmony said:

So if the new switch that Chrysler came out with was polarity sensitive, is that to say that it matters which wire goes to a particular post/stud?

I thought the switch was just acting as an interruption of power going to the brake lights. 

 

The pressure switch cannot be polarity sensitive, the the pressure from the brake fluid causes the switch to turn on, not the electrical supply.

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Yes, it was in fact polarity sensitive. The issue is the direct of the electron flow THROUGH the switch. They built a switch where the direction of flow through the switch was important to the life of the part. There is a small transfer of contact metal, just like in points, from the contact surfaces in the switch. I suspect that they figured that if the flow was one direction versus the other that the switch lasted longer.

 

I can dig up the Chrysler technical note if I have to. But all it says is they superseded the switch and tells you which wire to put where. I also assume that once they went to 12 volts in 1956 the higher voltage solved the problem.

 

James

Edited by James_Douglas
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