No fluid getting to rear brakes

[austinnelson117]

Ok so my '71 240 had been sitting for years and I am in the process of getting it driveable. I have gotten fluid to the front brakes and they work fine. But, no fluid will even come out of the bleeder on the rear brakes. Right now the pedal goes halfway down with little resistance and then is firm after that (Im assuming the no resistance part is the pushrod moving through the rear brake part of the master and then it gets firm once it gets to the front). Could this be anything but the master? And if it is the master why would the fronts be working? I know the manual says that they are essentially two SEPARATE systems but I'm a little confused as to how that works.

[austinnelson117]

Also, I dont think the lines are clogged. The fronts were and a firm slam of the pedal blew it all out. but, still no movement in the rear lines.

[Reverend]

Have you bleeded the system or did you just add new fluid?

[beermanpete]

It sounds like your master cylinder is bad. It has two circuits, one for the front and one for the rear. Inside the master there are two pistons, one for each circuit. The "first" piston is connected to the brake pedal via a push rod. When you push the brake pedal the piston is pushed forward and creates pressure in the cylinder. The second piston is pushed by the pressure created by the first piston. The brake pedal stops moving when the pressure in both systems is high enough to push all the brake pads and shoes into the rotors and drums.

If the first piston does not create pressure it will move until it physically touches the second piston. When this happens the second piston begins to move and create pressure. If the second piston does not create pressure (but the first one does) it will move until if bottoms out in the cylinder and stop, at which point the first piston will create pressure. In either of these cases the brake pedal moves futher, about 1/2 way to the floor, before the pads or shoes for the functioning system are pushed into the rotors or drums.

Try bleeding the master cylinder. If you cannot get fluid to flow from both the front and rear circuits the master is bad.

[austinnelson117]

I did bleed the master and thanks for the info Pete I just assumed it was one pushrod. Sounds like I'll be getting a new master.

[LeonV]

This sounds like the emergency switch has shut off the rear circuit, a new master may not solve anything. Search for "brake emergency switch", "rear brakes not bleeding", or something like that. I know it has been discussed before.

[PastorMike]

I had your exact problem, so I spent the weekend rebuilding the master with a kit found on eBay. It was a tough rebuild since the rubber seals are quite difficult to assemble onto the pistons. I would recommend purchasing a new master unless you want to stay original.

Another symptom of mine was the fresh fluid turning brown in the reservoir closest to the firewall (rear system feed). After rebuild, plenty of dark colored fluid out the rear left during bleed. My car was sitting for 13 years; more work to do on the slaves.

[austinnelson117]

Ill check your suggestion Leon. But my symptoms sound just like mikes. I took out the master cleaned it refilled it and still have brown fluid in the resiviour.

[PastorMike]

I theorized that the brown color was due to rust forming somewhere in the master's rear circuit; probably under the rear-most rubber piston-seal. All of the interior parts of the master cleaned up OK, except the rear nylon cup part, which is still stained brown.

Remember, DOT3 brake fluid is hydroscopic (absorbs H2O) and should be flushed every 2 to 4 years.

[Oiluj]

I had a similar problem with mine, as the car sat for too long. Had to replace the master and also had a sticky emergency switch block. Emergency switch had a bunch of crud built-up in it over the years.

[austinnelson117]

Where is this emergency switch everyone is talking about? I couldn't find anything on it

[beermanpete]

Where is this emergency switch everyone is talking about? I couldn't find anything on it

Directly below the master cylinder, attached to the inner fender. It has 5 brake lines and 1 wire attached to it.