Hold The Brakes

Before I took my car out for its first run in 6 weeks I did a quick check of the lights. Uh oh. No brake lights. When the rebuild the brake pedal assembly I noticed a loose terminal on the brake light switch. I ordered a new one along with new plastic bushings. When I installed the new switch the new bushings got rid of all the slop. However, the switch design relies on a certain amount of play. As the brake pedal moves forward the master cylinder push rod resists for about 1/16" which depresses the spring in the switch. Without that 1/16" of play the switch wouldn't work.

First I tried making a shim so the master cylinder push rod wouldn't have to move as fas to hit the switch. I cut apart the old switch and salvaged a plate that I stacked on top of the same plate in the new switch. But when I installed this new setup the brake lights stayed on all the time. There just wasn't enough play in the linkage. So I took the switch back out and removed one of the plastic bushings, more like a sleeve actually, that went in the hole in the push rod and slid over the pin on the brake pedal. With this bushing in place there was zero play in the linkage. This time when I put the switch back in it worked. I left the shim in place and the switch is pretty sensitive--it doesn't take much pedal pressure to activate the lights. I'm concerned the brake lights might accidentally stay on but I'm not sure there's enough movement without the shim. The master cylinder push rod is a newer replacement and looks nothing like a stock push rod.

Contributing to the problem is the fact that I have a power brake booster. I have searched and searched online for the manufacturer and installation instructions but have been unsuccessful. It could be because my setup is at least 10 years old and is either not produced anymore or has been updated so mine doesn't match any photos. It came with a bracket that mounted on the brake pedal and moved the mounting point for the master cylinder push rod. The reason for this is to reduce the pedal travel. However it has two negative side effects. First, it increases pedal effort by almost double, and second it creates a severe misalignment in the push rod. When I reassembled the brake linkage I left this adapter off so that's probably why I had so much trouble getting the switch to work.

Here's a shot of the old setup. The adapter is the silver chunk of metal to the left of the brake pedal. The gold master cylinder push rod is attached to the bottom left of the adapter. As you can see the adapter moves the end of the push rod about 3/4" to the left, putting it out of alignment with the master cylinder.