On Friday morning, my brake pedal went to the floor as I arrived at work. It seemed I had pedal resistance once or twice out of every ten pumps, and I knew the master had bit the dust. I left me car at work that night, and came back on Saturday with the very clean master cylinder from the donor car that supplied my four speed swap parts, and the swap went pretty well, but left me with a few questions.

my car is a '77, and has the oval reservoir with one switch built in to the reservoir and another switch threaded in to the master cylinder itself. The donor cylinder and reservoir is one of the later triangular versions, and has no switch port in the cylinder, and two switches built in to the reservoir. Mechanically, it functions fine, but I am wondering if anyone has figured out how to change the wiring around to get the warning lights to function again.

I know I could just get the right parts and put them in, but holy crap do they ever cost a lot. The gently used unit I installed is a legitimate New dealer part with only a few months of use on it, and I would prefer to keep using it, and keep several hundred dollars in my pocket.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

after two cups of coffee, I finally get what it is that I am trying to figure out. The later model reservoir has two chambers, thus two fluid level switches instead of one, And that is easy to remedy with a little splicing. What I don't know is if Mercedes did away with a brake pressure differential switch in the later cars, or if they just moved it off of the master cylinder to some other location.

Sometimes it stinks having an early W123 loaded with weird parts that didn't see use past 75-78. I guess I will be breaking out the FSM disc to see if I can compare and contrast the electrical nonsense enough to effect a retrofit.

I will say this, though. I thought I had a caliper hanging up a little as hard braking used to lead to a bit of a pull to the left. with the replacement master cylinder, that pull is gone, and the brakes are much more sensitive overall. I guess that means I have been driving the car off and on for two years with a bad master cylinder. I had no idea that a master cylinder could cling to life for that long.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread