Brake Light Switch

[darrin bob]

My Darrin brake lights do not come on unless extreme pressure is applied to the brake pedal.  They haven't worked right for years, even after the switch was replaced with a new one.  Trying to fix it before someone rear ends me!

With age, do the diaphragms on these switches get get stiff, OR do the electrical contacts get tarnished, OR do I just have a switch with too high a set pressure?

Can someone please head me off in the right direction.

Thanks,  Bob Benz     

[darrin502]

Not sure I have an exact answer but the brake pressure in the Darrin is caused by all of the brakes both front and rear it is a single compartment master cylinder.  My thought is that you may be losing pressure at one of the brake cylinder or pressure bypassing in the master cylinder. All brake adjustments are critical in producing even pressure in the system. My suggestion is to check all wheel cylinders and the master cylinder. Flush the brake system put in new fluid readjust all the brakes so that the brakes all work simultaneously. If your brakes are tight in the rear or front and loose in the front or rear this will cause you to have to press harder on the pedal to produce total system pressure at the switch.
Good luck.
Lee

[MarkH]

I've seen some surprising crud come out of old hydraulic parts. Maybe something more solid than clear clean fluid is reducing/retarding the pressure being delivered to the port in the switch. I would search with the factory part number for another switch, and then make sure you're pumping clean fluid out of the fitting before you install it. Also check the port in the fitting to make sure it's not restricted with built up hard deposits, which I've also seen.

[darrin bob]

Hi Everyone:

Thanks for your replies!

I  disconnected the wires from the switch and ran jumpers from them up out of the engine bay so I could see the tail lights.  I then could make and brake the circuit bypassing the switch.  Consistently I got full bright brake light, confirming the grounds are still okay.

The brakes work very evenly, but crud in the system is still a possibility I suppose, but I'm leaning towards a bad switch.

These switches are available from many sources, but they all either don't specify the actuation pressure at all, or various ranges like 20-45 psi, or 60-100 psi as examples!  I'm assuming that lower is better .  As a "bench mark", does anyone know what the original Kaiser specs were, OR a vendor you may have purchased a satisfactory unit from who may know.  Note that one Hot Rodder blog suggested a Harley Davidson switch which was described  as "lower pressure" so the lights will come on sooner.  Anyhow, I'd appreciate any help in this.

Thanks,  Bob Benz   

[joefrazer]

I’ve purchased switches from Autozone and all worked well. Use part number F4805, ten bucks.

[darrin bob]

Hi All:

Thanks again for your responses.

FYI:

Checked AutoZone.  They have part # F4805 in stock locally.  They have absolutely no specification information.  Did some research and found that the actuation pressure is 60 -120 psi.  Could find no information on whether or not they are compatible with silicone brake fluid.  Joe: Are you using these switches with silicone fluid?  Please let us know.

Also found a lower pressure switch which is specified as compatible with silicone fluid and has a actuation pressure of 20-50 psi.  It is available from Hot Rod Express in North Carolina, telephone # 704-483-3300, SKU # SW32, at the ridiculous  price of $29.95!!!!  Anyhow, it's available and the brake light should come on much earlier.

Look forward to hearing from you on the silicone question.

Thanks to all,   Bob Benz

[joefrazer]

I have used the switch with types 3, 4 and 5 fluids with no negative effect to the switch. I have one on the Traveler, HJ and the Darrin and all work just fine.

[darrin bob]

Joe:

 Great!

Thanks,  Bob Benz

[r1lark]

I got tired of the lousy hydraulic brake light switches that are available these days, and have started converting my older cars to mechanical switches. The thing that really drove me to this was the day I heard tires schreeching and looked in my review mirror and saw a minivan sliding to a stop, and I could actually tell from her mouth that she was saying "No brake lights!". Sure enough, the switch had failed (and the failure mode was that it had gotten to the point where only pushing as hard as I could on the pedal would make the brake lights come on).

Here is a link to what I did (sorry guys but yes it's on a Studebaker):
http://forum.studebakerdriversclub.com/showthread.php?48294-Mechanical-Brake-Light-Switch-(Underfloor-Pedals)&highlight=brake+switch+sedan

I got mine from a specialty hot rod place, but the switches for late '40s/early '50s Chevy pickups are about the same -- here is one on RockAuto.com: 
https://www.rockauto.com/en/catalog/chevrolet,1950,truck,3.5l+217cid+l6,1487136,electrical-switch+&+relay,brake+light+switch,10474

[MarkH]

I got tired of the lousy hydraulic brake light switches that are available these days, and have started converting my older cars to mechanical switches. The thing that really drove me to this was the day I heard tires schreeching and looked in my review mirror and saw a minivan sliding to a stop, and I could actually tell from her mouth that she was saying "No brake lights!". Sure enough, the switch had failed (and the failure mode was that it had gotten to the point where only pushing as hard as I could on the pedal would make the brake lights come on).

Here is a link to what I did (sorry guys but yes it's on a Studebaker):
http://forum.studebakerdriversclub.com/showthread.php?48294-Mechanical-Brake-Light-Switch-(Underfloor-Pedals)&highlight=brake+switch+sedan

I got mine from a specialty hot rod place, but the switches for late '40s/early '50s Chevy pickups are about the same -- here is one on RockAuto.com: 
https://www.rockauto.com/en/catalog/chevrolet,1950,truck,3.5l+217cid+l6,1487136,electrical-switch+&+relay,brake+light+switch,10474

That switch looks like a good idea. I wouldn't mind seeing your install pic, could you post it here? I can't see it on your link unless I join the Studebaker forum & log in.

[darrin145]

The last time I got hit from behind the lady told the cop she didn't see my brake lights...I asked her if she saw my car getting bigger through her windshield!

[r1lark]

Sorry Mark, I didn't realize the pic would not be visible. Here is the picture, not sure why it's rotated. It should be rotated 90 degrees counterclockwise.

EDIT: I just got to thinking about the Darrin clutch and  brake pedals - do they come up thru the floor, or are the pedals mounted on the firewall? I have never seen under the hood/underneath of a Darrin. 

[MarkH]

That looks pretty good, and I like the idea of the brakes lighting up as soon as the pedal starts moving.
  Discovered for the second time a micro crack weeping fluid in the side of the elbow that the pressure switch threads into on my Aero, both used originals, closely inspected on #2. Had the wife standing on the pedal both times, chasing down high pressure leaks at a few fittings and thought it was done till I saw a drop of fluid on the floor this weekend.
  Just ordered one of those switches, I think it will fit. Hopefully when I replace the elbow & pressure switch with a brass plug that will be the last time I have to bleed the system. Now if I could just find a decent 6V LED 3rd brake light.

Thanks for posting!