Brake Warning Switch O-Ring - Where to Get?

[PurpleBeeper]

I had a leak in/near my brake warning switch (sensor) in my '70 Road Runner power disc front/drum rear car. I replaced it with a real New-Old-Stock part & a year later it's leaking again. I'm pretty sure it's the O-rings that are failing. I seem to recall that the O-rings are a little "flat" looking compared to a regular "round" o-ring.

I don't need to be original. Where can I find an o-ring for the '68-'70 brake warning switch (sensor)? What exactly should I be looking for?

THANKS!

 

[gtxno1]

take it out and go to napa and match one up

 

[PurpleBeeper]

take it out and go to napa and match one up

True, but having worked in several auto parts stores I know that what they carry in most cases is Viton rubber in a variety of sizes. All the places I've worked at (AutoZone, O'Reilly & Murray's) had the same red case full of O-rings separated by size.

What I don't know is:
1. Will Viton rubber be able to handle the chemical exposure to brake fluid? (it sure attacks paint)
2. Will Viton O-rings be able to handle the super high pressure of a hydraulic brake system?
3. Will an off-the-shelf o-ring seat properly and seal in this situation?

I remember that the OEM O-rings are sort of flat....not really a traditional o-ring. I realized this when I pulled out the original leaking brake warning switch, but I didn't hunt for a replacement o-ring then since I already had an original OEM NOS brake switch with a new, factory, flat-looking o-ring.

 

[gtxno1]

I do not think being round will hurt as long as it fits and seals if you are using dupont viton not a problem will work out fine do not use nitrile

 

[Photon440]

I do not think being round will hurt as long as it fits and seals if you are using dupont viton not a problem will work out fine do not use nitrile

I'd stick to the original design. For instance, replacing the square cut o-ring in a Thermoquad with a generic round one leads to lots of problems. It costs more to have flat o-rings, the engineers (or bean counters) wouldn't use them if they could get away without them.

Is this the valve that's being discussed? There's a link to a rebuild kit at the bottom.
https://musclecarresearch.com/1970-76-mopar-combo-valve-autopsy

 

[gtxno1]

A square cut o-ring is a whole other matter slightly flattened is fine could just be from being on the switch causing the slight flat spot but if it is a square cut then you will need a square cut

 

[PurpleBeeper]

Is this the valve that's being discussed? There's a link to a rebuild kit at the bottom.
https://musclecarresearch.com/1970-76-mopar-combo-valve-autopsy

Photon440, you're da' bomb! That's exactly what I'm looking for. I really only need one o-ring (the one for the brake warning light switch), but that's OK, I ordered a kit. Even though it's not the kit for my proportioning valve, I'm sure the o-ring I need is the same. Also, from the pictures, the O-rings look pretty "round & normal".... so I may also try an off-the-shelf Viton o-ring first since I can get that up the street from my house.

 

[Hemirunner]

Reviving an old thread here, and I have a leak at the sender on this block. Does anyone know what the sensor thread is or what I can use as a plug since I don’t need it in my application. Thanks!