So I have a 50s Ford with Drum/Drum. It use to have a single master cylinder but after following the directions here I swapped it to a early 70s Mustang Drum/Drum dual. The front brakes are still on the block but the hole that had the line that went to the rear brakes has the brake light switch now. The rear line is coupled to the MC and running as it was. I am having an issue with the hydraulic brake light switch getting pressure intermittently and remaining on, even very faintly by the brightness of the lights, other times very much. Pumping the brakes seems to cut it off when it gets stuck, but not always. I have replaced the switch but no soap, I think it's fluid pressure. Any suggestions of the correct fix?
Yeah, throw away the switch and put a good mechanical one on the pedal linkage. Those hydraulic switches are hit or miss anymore, you might get a good one and you might not. If you are determined to run a hydraulic switch, find an old working original one, it will be made with better components and will last longer than the import stuff sold now.
Yeah, I had a "good mechanical one" and after short order it failed and the power line heated up and started melting. Those are made by the same overseas political prisoners of the people's republic that make the hydraulic ones and most all other car parts today.
There shouldn't be enough residual pressure to activate the brake light switch/s. Is it possible the master cylinder actuating rod doesn't have enough free travel? Heat expansion can slightly pressurize the system. There needs to be a small amount of free travel to prevent it.
The pressure switch being downwind of a residual pressure valve would explain the cause of your problem. The Harley switches seem to be well made. Chris
I would check the piston depth from the original to the replacement. Don't assume they are the same. Also mounting depths as well. My guess is they are different and could and will create problems.
The Jalopy Journal
