Thread: Under the floor Master Cylinder - how to mount brake switch?

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I'm with Viking---have been building rods for 40 years with pressure actuated hydraulic brake switches---have never had one fail.

I never had a problem with a hydraulic brake light switch either.

I think this "failing hydraulic brakelight switch" is an urban legend.

Originally posted by brianrupnow
I think this "failing hydraulic brakelight switch" is an urban legend.

Ditto, more problems with the wiring that with the switch.

Viking and Brian, Where in the line did you put the hydraulic switch? I put mine between the master cylinder and the rear pressure regulator like the Speedway diagram showed, but if the regulator keeps the pressure high maybe it will flicker or stay on? I bought a mechanical switch so I could set it up like C9x shows but I already have the hydraulic switch in the hydraulic circuit. I won't know until I get my wiring in.

Don Shillady
Retired Scientist/teen rodder

I just cut in to the line out of the master cylinder, add a tee fitting for the hydraulic switch and wire it.

Originally posted by brianrupnow
I think this "failing hydraulic brakelight switch" is an urban legend.

they dont fail...harleys have run em forever...they even work on my chopper flawlessly

I just cut in to the line out of the master cylinder, add a tee fitting for the hydraulic switch and wire it.

Don---I put the tee for my brakelight switch in the front brakeline immediately after the master cylinder, before the residual check valve. Note that the residual check valve holds pressure between it and the wheel cylinder, not between it and the master cylinder.

Joe, no parts # handy, but I'm pretty sure it's a 70's - 80's era Chevy pass car switch and it's probably used in other GM cars of the era as well.

Originally posted by djpritchard1
C9x - I also like your solution, by the description, but I'm having trouble understanding exactly what I'm seeing in the photo. Is the switch on the back side of the brake pedal? I assume I'm looking at a portion of the brake pedal arm, but am having difficulty distinguishing which is the pedal end, and where the actual switch is in the photo. To the lower left had portion of the photo, that little cicular protrusion, with the nut over it - I'm thinking this is the switch? If so, what does the switch hit to activate it.

Thanks

Dave

That pic is a litle confusing to say the least.

We're looking at the car - 32 roadster with fiberglass encapsulated floorboards - from underneath.
Front of the car is to the left.


The switch is operated by the 10-24 stainless bolt that goes into a tapped hole in the brake arm.

The brake arm pivot point is to the right and that gizmo with the allen bolt in it is the brake pedal return stop.
(I'll post an additional pic or two.)

What I think you're calling the protrusion is one of two - both visible - 1/4-20 nlock nuts that retain an aluminum escutcheon that finishes off the opening and holds the carpet down.

The round can upper right is the switch proper.
It's bolted through the floor with a couple of 8-32 buttonhead allens and you can see their ends in the factory threaded mounting flange.

Reason the switch looks odd is the excess end of the arm was sawn off.

Fwiw, nothing wrong with the hydraulic switches if you run regular brake fluid.

Run silicon fluid - as I do - an the silicon fluid will seep into the switch area and electrically isolate the contacts one from the other and they won't work until the pedal is pushed hard enough to lock the wheels.
The mechanical switch cured that problem.

Incidentally, imho there is no such thing as a low pressure hydraulic switch.
They're all set to close contacts at about 7#.



Here's a pic of a similar brake arm return stop in my 31 on 32 rails roadster project to give you an idea of what you're looking at in the above pic.

This pic shows the return spring setup as well as the brake arm etc. on the Deuce Factory brake/clutch pivot bracket.

It's missing the bolt in side piece that was left off for the photo.

This pic shows what's required for the coil spring return spring setup.

The brake pushrod gets the end sawn off and threaded for the Heim joint. (The threads are there, just hard to see in the pic.)

An aluminum cup was machined to retain the outer end of the coil spring.

Master cylinder is a typical FoMoCo, a Mustang with 7/8" bore in this case.
Note that the coil spring has to be opened up a bit so it will fit over the mouth of the Master Cylinder.

The coil springs are available at many places, Home Depot being one.

C9x---here is a direct quote from Horton Rod Shops catalogue, regarding the hydraulic brake-light switch that they sell.
"High quality switch. Much longer life than previous models available.Fits most cars.Only 20 to 50 pound pressure required instead of stock units that don't come on untill 60-100 pounds of pressure."

Couple things I meant to add.

Be sure and install a zerk fitting in the brake pivot.
I didn't on the 32 and was about a three hour job to do it after the car was up and running.

The Mustang M/C has the brake line fittings exit toward the center of the car.
Not a problem in most cases, but you can get the same M/C - also with 7/8" bore - with the brake lines exiting toward the left side frame rail.
The 32 has such an M/C and it's out of a Torino.
Some of the other FoMoCo cars of the era - 70's or so - have the same deal with the brake lines exiting same direction as the Torino M/C.

Keep in mind the FoMoCo M/C's used in under the floor hot rod setups are in the reverse direction of the stock install.