Hydralic brake light switch

GPster · May 01, 2006, 04:23:26 PM

For simplicity, I'd like to use a hydralic brake light switch on the truck project. I'd rather not have to go to Ron Francis for a super sensitive one, I'd rather go to NAPA and get one that people have had fairly good luck with. This will go on a drum brake system with a single cylinder master cylinder and no power booster. A switch with 1/4" IPTM would work on my system easiest. Now, any one that would like to write a tech article for May you can examine this system for faults. The master cylinder has a fitting block on it for a 3/16" line for the left front brake and a 1/4" line that feeds a junction block on the right frame rail for the rear brakes (a single 3/16"line) and a 3/16 line for the right front brake. The best thing trying to analyze pressure/flow would seem to pipe the brake light switch into the 1/4" line but that is a line I've already changed. The 3/16" line to the left front brake needs replaced and the standard 53" long replacement line with fittings is too short so I'll use a coupler and a short line near the master cylinder to make it work. That's the reason I want a switch with a 1/4"IPTM thread. I've got a tee that is 3/16 x 3/16 x 1/4"IPTF that I could use instaed of a coupler and it would put the brake light switch in a handy place. The line from the master cylinder to the tee with the switch on it would probably be less than 6" long. Am I adding too much of a problem in this system using one of these questionable switches with this kind of plumbing? The '53 Chevy car that all of this is a part of had a mechanical brake light switch that fastened to the floor and all of this would be easier for me to figure out before I cover it with floor. GPster

MrMopar64 · May 01, 2006, 05:06:11 PM

What you describe sounds like the brake light switch setup on my Rambler
It's in a block on the front brake line.......Works fine

MM64

enjenjo · May 01, 2006, 08:18:22 PM

Sounds like it will work fine to me. as for a switch, Mopar up to about 56 used the switch you want on most everything.

terrarodder · May 01, 2006, 11:13:54 PM

One thing to remember, keep the switch part of the fitting pointing up, that way if you have to replace it, the brake fluid will not run out. I just had to replace mine an I didn't have to bleed the line again.

GPster · May 02, 2006, 07:36:21 AM

Quote from: "terrarodder"One thing to remember, keep the switch part of the fitting pointing up, that way if you have to replace it, the brake fluid will not run out. I just had to replace mine an I didn't have to bleed the line again.

In practise that might seem like a great idea but in theory any air bubble that might travel through that line would see that as a high place and go there. I would be concerned that a bubble of air at the sensor of that switch would complicate it's ability to react correctly. But of course that's the reason it takes me so long to do anything. I scare myself by examining what could go wrong. GPster

terrarodder · May 02, 2006, 10:59:32 AM

So far I replaced two an didn't have a problem, but I guess it could happen

sirstude · May 02, 2006, 11:32:14 AM

I think if you just use the switch to trigger a relay that runs the brake light, you won't have to replace the switch so often. They don't seem to handle the load of current lights too well. I did that on my Studebaker after I had to replace on switch and never did it again. Ken is still running the same switch 10 years later.

Doug

GPster · May 02, 2006, 05:37:35 PM

Well I went to the local NAPA Store today looking for a brake light switch for a Chrysler Product something built before 1956. The only one there that had been built before '56 was me. Their electrical components didn't show any brake light switches so I think he made the assumption that Chrysler didn't start using brakes til '57. I told him to look under Dodge trucks and I told him to look under brake components rather than electrical components. He found something on the computer that looked suspicious but it was 1/8" pipe thread and used those strange push on electrical connections. He then checked his stock and they've never had one. The he checked their Columbus warehouse and they had ONE (only one) there and he could maybe have it tomorrow. Time to play my ace in the hole. My neighbor used to have a gas station but is now just doing repairs out of a garage next to his house. I checked his stock and he had one that took those funny electrical clips and was 1/8" pipe thread. It wasn't what I wanted but he seemed to have as much in stock as NAPA's warehouse so I dealt locally. I'll just do a little plumbing change. Now to comment on some of the other ideas. My understanding of most of the faults with the hydraulic brake switches was that they weren't sensitive enough to pedal pressure and with the onset of disc brakes you'd * near have to be in a panic stop mode to make the brake lights come on. I thank with 4 wheel drum brakes this system will be closer to the design capability of the switch. Now the electrical problems of the switches is new to me but entirely possible. With 3rd brake lights and 2057 bulbs I'm sure the amp draw is pushing the contact strength of the switch. Letting the switch operate a relay is an excellent suggestion but I think for simplicity I'll just use a couple of trailer lights on the corners of the bed with 1034 bulbs in them. Tomorrow a trip to a Weather Head catalog. I've typed so long I've bored myself. GPster

Jokester · May 03, 2006, 12:18:51 AM

Go back to the Napa store and ask to see their Echlin Engine Management Buyer's Guide. It's and actual paper book and has tons of info in it that are not in their computer tube. The parts are in alphabetical order. Start at stoplight switch # SLxxxx. In a couple of pages you'll see some hydraulic ones. There are two or three in the line with different connectors. I think all have 1/8" pipe thread. Get a pipe bushing (preferably brass) to convert from the 1/8" switch to your 1/4" fitting. The buyer's guide also gives you the pressure range that it closes.

I can't find my book, but I'll try to look it up tomorrow.

Definitely use the relay. Don't use silicone fluid, I don't believe the switch is made for it.

For what it's worth, I prefer mechanical switches to hydraulic. I've seen cases where moderate pressure on the pedal was enough to apply the brakes and stop the car, but not enough to light the lights. Found that out when I installed my third brake light in the back window. Realized that it wasn't coming on half the time. Didn't realize it until I couldn't see the reflection in the rear window.

My 2 cents.

.bjb

Jokester · May 03, 2006, 10:21:58 AM

The Napa SL134 is the most popular number in hydraulic brake light switches. Most stores stock it. It requires female .156" bullet terminals to connect it. Next popular is SL139 but it uses a molded connector (Napa # ARC120 might be it). There is also a SL143 that uses slide-on blade terminals. All of them switch at 60-120 psi and all are 1/8" pipe thread. You can go to www.napaonline.com to check pricing and stock at your local store.

.bjb

GPster · May 03, 2006, 01:56:36 PM

Quote from: "Jokester"(Napa # ARC120 might be it). .bjb

Thanks for that number, I'll go over and check on it. I'm computer ignorant and all your numbers give me the could ship within 24 hours. Just for the heck of it I tried to see if the switch I got from my neighbor (Borg Warner S193) would cross to one of those NAPA numbers to see if that molded plug would fit it. It wouldn't recognize that number. Went deeper into my coffee can of inverted flare fittings and found a brass teethat had 3/16s on the run and 1/8"IPTF on the branch and had a way to mount it, so it's closing in on me

58 Yeoman · May 06, 2006, 09:50:23 PM

Ran across this while checking for 41 Pontiac stuff on ebay.

http://cgi.ebay.com/ebaymotors/NOS-Stoplight-Switch-35-1935-40-1941-Cadillac-Pontiac_W0QQcmdZViewItemQQcategoryZ34205QQitemZ4638036410QQrdZ1

GPster · May 07, 2006, 10:07:38 AM

Quote from: "58 Yeoman"Ran across this while checking for 41 Pontiac stuff on ebay.

I'd hate to mess up someone's 100 point restoration by buying that for a spare. I checked his 107 other auctions and he didn't have any front wheel cylinders. When my project was still a car all the back brake lines were rusted. I didn't even want to try and drive it even just in the yard with no back brakes and an automatic transmission (slow re-action times,even if sober) so I replaced the lines. The wheel cylinders in the rear started weeping so I found kits for them and vowed to rebuild them the next time I had the drums off. When I decided to use this frame for the truck project and slide the front suspension foreward I decided on new steel lines in the front rather than short additions and couplings so I just plugged the lines so the back brakes would work some. Well lately the new lines and the brake light switch was the project. Found the switch, bent new lines got fluid in the bleeder on the passenger front to go back to the junction so I closed it up and started on the switch and driver's side. Got the line all laid out and the switch mounted and tried to fill the line though the bleeder like worked on the other side, no go. Tried my little vacuum bleeder and it wouldn't suck. Pulled the bleeder to see if it was pulgged and it was clear and had fluid on the back side. Hooked the steel line up to master cylinder (which I rebuilt after the flood) to try to push the fluid foreward through the new line and the the new switch and I could only get fluid as far as the flexible brake line so I took it off to check it. The inside of the line had swelled closed from one end to the other. The lines on both sides didn't match so one of them had been changed before so I made the decission to replace both of them. After a day of playing around with trying to save money, deal with off brand replacements and adding shipping time to the project I went to a third supplier and got Wagner hoses delivered to my house on Saturday ( two for $50.26 plus tax). I'm now so excited I couldn't wait. Pulled the old flex hoses and installed the new, back filled the sysem through the bleeders and closed it up and stood on the brake pedal, I now have to nice brake fluid puddles with two front tires sitting in them, blew out both front wheel cylinders. Time to get ready to go to church and pray for it,there'll be more. GPster

terrarodder · May 07, 2006, 09:05:56 PM

Quote from: "Jokester"Go back to the Napa store and ask to see their Echlin Engine Management Buyer's Guide. It's and actual paper book and has tons of info in it that are not in their computer tube. The parts are in alphabetical order. Start at stoplight switch # SLxxxx. In a couple of pages you'll see some hydraulic ones. There are two or three in the line with different connectors. I think all have 1/8" pipe thread. Get a pipe bushing (preferably brass) to convert from the 1/8" switch to your 1/4" fitting. The buyer's guide also gives you the pressure range that it closes.

I can't find my book, but I'll try to look it up tomorrow.

Definitely use the relay. Don't use silicone fluid, I don't believe the switch is made for it.

Ron Francis has a relay for brake light also clams there switch can be used with silicone brake fliud, I don't know about that had to replace mine after 2 years, waiting for a reply from them on that.
For what it's worth, I prefer mechanical switches to hydraulic. I've seen cases where moderate pressure on the pedal was enough to apply the brakes and stop the car, but not enough to light the lights. Found that out when I installed my third brake light in the back window. Realized that it wasn't coming on half the time. Didn't realize it until I couldn't see the reflection in the rear window.

My 2 cents.

.bjb

Skip · June 03, 2006, 10:16:53 PM

Do yourself a big favor and put a relay between the brake switch and the lights (or the turn signal switch which is where the wire should run anyway)

I haven't had alot of luck with brake switches in the last 10 years or so. Qality seems to have gone downhill. A relay will protect the contacts from arcing and the pedal effort to activate the lights will remain constant.

W/o the relay, the pedal effort will gradually increase to the point where the lights will become intermittent.