VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 41 brake light switch

Good morning/afternoon everyone. Hope you guys are doing well. I've been quiet for a while, busy living life.
The brake lights on my 41 SD quit working. They had been working, but required significant effort to get them to work. I'll get suited up later today to make sure they actually work by shorting the contacts of the switch.
Gene or anyone else, do you have a photo of your mechanical brake light mounted? Just trying to prepare myself for when I get up under there.

There are pictures of the 1942-48 switch mounted in the 1942-1948 shop manual.

I believe 1941 originally had a pressure style switch screwed into the side of the master cylinder. The end of the wires had eyes and the switch terminals had small screws. Later models used the lever style switch mounted on the lower firewall actuated by the brake pedal. If I recall correctly, replacement pressure type switches have bullet type connections and are available locally. If you still need a picture of a mounted lever type switch I should be able to find one from my 48.
Mike

Thanks Gene and Mike. I forgot about the online manuals. I'll look at those a little later and try to find a good pic.
Have a great day

The attached picture is the switch on a 1948. Mike

Thanks Mike. That helps a lot.

The pressure switches are infamous for doing that with a bit of age. That's the reason I converted my 38 to a mechanical switch. You'll be glad you did if you convert. Just run short jumpers from your existing pressure switch wires to the mechanical switch.

I’m not trying to be argumentative but will offer an alternative perspective. I agree with with the comment on the longevity of the pressure switches, their life expectancy is less than the lever type. It took me about 15 minutes to change out the original pressure switch on my 41 including jacking the car, installing the switch and converting to bullet connectors. It was very accessible. Had I installed the lever type switch, I doubt I could have even moved the floor mat to locate the position of the holes that need drilling in that amount of time. To my knowledge the location of the holes are not pre marked on the 41 floor pan.

When/if you have to change it two or three times a year like I was you might be more receptive to the idea. It's also dangerous when it goes bad because your brake lights don't work unless you stand on the pedal and "lock em up". Each to their own.

my experience with pressure switches is the same as Tiny's as they were common in British cars and often failed, either leaking or not contacting. The pedal operated switch seems to be a lot more reliable.
Tony

Thanks Mike for the feedback. Do I need to bleed the brakes after I replace the pressure switch? I guess that's what I was trying to avoid. Maybe I'm misinformed.

Scott, It’s probably been 3 or 4 years since I replaced the switch on my 41. If I recall I did not have to bleed the brakes. I wouldn’t pump or move the brake pedal with the switch removed. Mike

Hi Scott

You shouldn't have to bleed the brakes.
Once you have the switch installed, make sure the master cylinder is full of fluid.
Then slowly depress the brake pedal about half way.
Don't fully depress it right away so you don't drive any air in the system too far down the brake line.
Then quickly release the pedal and wait at least 20 seconds to allow the fluid and any air to return to the master cylinder (it takes a little time).
Repeat several times while depressing a little more each time.

I've done this lots of times, even after removing the line from the master cylinder.
Always works for me.

My experiences with hydraulic brake light switches convinced me to add a mechanical switch to my '37 Master coupe as well as another "57 classic car we own.

I discovered 2 issues with these hydraulic switches. One is the reliability. The other is that most switches you get today are activated by higher pressure than the brake systems in these older Chevy's. Typically they require at least 60 psi if not more to close. The original ones in these cars closed at no more than 30 psi.

I drive so much in traffic that I wanted the dependability of a mechanical switch. I ordered one from rock Auto that fit a '49 3100 and easily fit it to the '37.

Ron Francis claims to have a more sensitive hydraulic switch that closes at somewhere between 20 and 50 psi.

When it came time to replace the pressure switch on my 41 I also had the same concern as Rusty regarding the actuating pressure of the replacement switches. I tried to do some online research regarding the different brands but didn’t have much luck. Since the cost of a new switch from my local NAPA store was less than $15, I decided to try one before changing to the lever type. My rational was I could always add the lever type if it didn’t work or took too much pedal pressure. I haven’t changed yet. Probably luck.

One other comment on dependability of replacement parts. Standard Motor Products is a long time common brand of switches, points, condensers etc. Recently I discovered they use nearly the same part number for two different grades and quality of the same part. For example, ignition points for a 48 Chevrolet are listed as DR2227P and a much newer version DR2227PT. The points ending with P are the original heavy gold colored version with a two component spring while the PT version is lighter, with single spring Same goes for other parts including the pressure switches. There is a SLS27 and a SLS27T pressure switch, both showing the same fitment. Condensers are listed as DR60 and DR60T. Search the web for the T series dependability. I know, buy nos Delco when available.

I'm definitely with Minetto here. He knows his stuff and leans toward originality whenever possible.

I'v been using the pressure switch with no problems for years on end. Those who lean toward the lever switch may be merely trying to justify their departure from originality by playing the safety card or trying to justify the change to the lever owing to them having gone to the trouble to switch over.

Pressure switches work just fine and are easy to replace if you need to.

As long as I have been owning and driving 41s - going back to the fifties - I have changed the pressure switch once only.

Just my two cents worth. No intent to step on toes here.

Best,

Charlie

A followup. I went to Napa and got a replacement switch (took a while to find it) but was only $13. Replaced it and found it odd that the threads weren’t taped and also that not much/any brake fluid leaked out.
I wonder if the brake light switch was a leak path for brake fluid and my old switch wasn’t even bad (luckily it was cheap). After replacing the switch it still didn’t work. I topped up the master cylinder and it started working like a champ. So questions….was I right in teflon taping the switch threads? Should I put same tape on the master cylinder cap (thinking moisture ingress).

Thanks

Without seeing what was done I wont comment on why it started working after topping up the fluid. The straight threads on the new switch indicate the switch is designed to screw in and seal onto a copper washer and not the threads, teflon tape wont be a problem unless you left some hanging below the threads and it floats through the system.
Tony

I stopped using Teflon tape and started using plain old plumber's pipe dope. It's been preventing leaks for 150 years.

The pressure type switch is 1/8" tapered pipe thread so the teflon tape should be fine as long as it's not leaking. As mentioned, pipe dope is a better alternative in the future. With regard to the reservoir plug, it should have a fiber / gasket material ring in the recess below the threads. These are available from our suppliers but can be cut from sheet material. I suspect it took a few pumps of the brake pedal to purge the compressible air from the switch before it saw actual hydraulic pressure. Filling the reservoir may have been a coincidence unless it was very low.

I have had great luck using teflon tape.
Strangely, I have NOT had good luck with teflon thread paste.

I used the paste on a hot water heater install in the house and had a very slow seep at nearly every thread I used it on.
I had to take everything apart, clean up, and reassemble using tape.

I have no idea why this should be, but it sure put me off of using the paste.

Like the factory I have never used anything on brake or fuel system threads and never had leak problems.

:

Same experience for me.



Charlie :computer