I'm sorting out my new 32 and have run into a problem that I've never seen before. I've got drums all around with an external residual valve on the front and an internal (in the master cylinder) residual valve on the rear. My hydraulic brake light switch is plumbed in the rear brake line. After driving a bit my brake lights stay on even with the the pedal all the way up. I've checked and nothing is stopping the pedal from coming all the way up. I would say its the switch but when the car has been sitting for a while the brake lights turn on and off just fine. Its almost like repeated braking in city driving is building up pressure that doesn't immediately drop but as the car sits the pressure slowly drops to the point where the brake lights go off. It doesn't seem that the brakes are draging at all. So what do you think the problem is??
If it is a hydraulic switch it probably has a internal leak or the port into it has a bit of dirt resticting the flow. Anyway easy enough to change ,do it on the fly and you won't need to bleed.
With your brake lights on and pedal up disconnect the wires and put an ohm meter on the terminals. If you measure a short switch is bad, In my 50 plus years building cars I've never used a hydraulic brake light switch. The common one years ago was the Harley unit. Even on bikes they fail. I use lever switches on all my builds. Never had a failure and they're easy to change. The FOGGER
I never could get more than about a year on the hydraulic type switchs. Converted to the level style and have had no problems in 6 years.
I have heard this problem before. A lot of the time if you put the switch on vertically and upside down, they have tendencies to hold air in them. It then works pneumatically rather than hydraulically. The air won't have the pressure to equalize the switch back out and it will stay on. Bench bleed the switch or put it right-side up. -drZ
On every car or bike I've owned thats had a hydraulic brake pressure switch, the switch has failed. Last time I scored one about a year ago was a "universal" unit from NAPA, it was around $8.00.
this is what i just bought at napa: http://www.napaonline.com/MasterPag...PartNumber=SL134&Description=Stoplight+Switch
Same here. I had a problem with my switch in 1970 in my Morris Van coming home from the Popular Hot Rodding magazine Nationals. Replaced it and had a problem the next year. Always used a mechanical switch since.
I made my own bracket and used a vend switch from a Vendo soda machine. these are very high quality, momentary switches that are made to last.
I used a Ron Francis low pressure switch. Worked great, no problems in 6 years however, I changed exhaust. The tubes going from my lakeheaders, under the frame, caused the m/c to heat up. This caused the brake lights to stay on. I added a heat shield to the m/c and that cured the problem.
Check that your brake pedal has free play when the brake lites stay on. Sounds like the push rod needs adjusting.
I used one of these, they're cheap enough, I got an extra, haven't needed it in 6 years http://www.speedwaymotors.com/Universal-Mechanical-Brake-Light-Switch,1972.html
I used to a use hydraulic brake light switch until it failed on a road trip one day and I didn't know it. I have cruise control on my car for those long drives and when your switch goes bad your cruise won't disengage until you shut it off manually. In fact when you mash the brakes even harder, the car will go to full throttle. Not a good thing when you originally wanted to slow down to avoid running under the back of a semi!!! For that reason, I switched to a Ron Francis waterproof mechanical switch. At $28.95 its not cheap but pulling your *** out from under a big truck isn't cheap either. Not to mention a lack of brake lights might get your **** run over by semi that's on your back bumper. Here's the link to it: http://www.ronfrancis.com/prodinfo.asp?number=SW-42
I replaced one of the Ron Francis low pressure switch just last spring. It developed a leak that drove me crazy for almost 2 years. You couldn't see fluid leak but it let in air. I replaced it with a switch used in early 60's Buicks, Jeeps and IH trucks, just a bit higher acctuating pressure, but the same connector and only $8 instead of about $30.
I had the same problem and it was the push rod being too tight. I adjusted it a tinny bit and all is good.
Finally a topic on the Hamb that I can respond with some authority on - believe me, there aren't many. I worked for 10 years as a brake engineer. I am now a sales engineer - one of the companies that I represent manufacturers the old "Harley" switch that was previously mentioned and another manufactures all sorts of mechanical switches, so I know a bit about both brakes and switches. Most of the potential culprits have been covered here, but I will try to clear the air a bit. I apologize in advance if this gets lengthy. First of all - DOT 5 is silicone based, it tears up nothing. It is very gentle to seals and paint which makes it popular for rods as was the reason that Harley used in production up to about 5 years ago - it didn't ruin the paint. However, there is a price to pay - DOT 5 absorbs air much like glycol based DOT 3/4 absorb water. This results in a spongy feel if you have a poor bleed or just over time with DOT 5 exposed to atmosphere. Put some heat into the system with use, air will escape from the fluid only to be reabsorded upon cooling. You either need an exceptional bleed or excess volume in your master cylinder. Is this causing your problem? Probably not. It is, I think, highly unlikely that i dragging brake would cause this problem in a drum brake application. Not enough fluid in the wheel cylinder to heat up and cause much of a problem. Not likely a leak in the switch, but a nearly complete blockage in the switch port could cause this condition - again not likely. Make sure the switch is clear and not mounted with the switch end pointing up - point it to the side or preferably tilted down Push rod being tight is a likely culprit. If this is the case, you will have free play in the pedal when the condition is occuring and it would likely occur under just actuation with no driving, and therefore no heat. If there is no play in the pedal, you are down to two options: residual valve with a lower hold pressure or a brake switch with a higher set point. If your brake currently do not drag, I would go to the higher set point switch. If you go the other way, you could end up with more stroke to get brake pressure on application. Hope that helps. PM me if there anything that I can help with.
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