W126 master cylinder and reservoir

[Brian Carlton]

Well, I did it to myself, with the kind help of the SDL.

I'm fully aware of the two chambers in the M/C. Naturally, I believe that the front chamber controls the front brakes and the rear chamber (the smaller one) controls the rear brakes.

But, what I was not aware, is that the rear chamber does not extend all the way across the reservoir. The dam in the middle extends from the right side of the reservoir toward the left side and then it makes an abrubt 90 degree turn to the back of the reservoir.

So, when you look at the reservoir from the driver's side, you see only the front chamber.

To see the rear chamber, you must look at the reservoir by leaning into the engine compartment and looking at the reservoir from the passenger side. Then the separation of chambers is visible and the level of fluid in each chamber is visible.

Why all this BS you say?

Because I must have had a small leak in the rear brakes, after doing the brake job four months ago. I noticed the reservoir level drop slightly, but, never took much stock in it. I'll check it out when the weather gets warmer.

This morning: Lost half the system. Reason: no rear brakes

After pondering a new m/c, I determined to find out whether I'm not seeing the fluid levels properly in the reservoir, and, well, you know the rest of the story.

So, my question to those who have stuck themselves in the same situation and resolved it:

Can you bleed the rear brakes at the calipers and get away with it? Or, must the master be bled first and then the calipers?

If the master has to be bled on its own, can it be bled on the vehicle? If so, can just the rear brake system be bled?

TIA.