I had an odd experience bleeding the brake master cylinder of the 83 300SD from bone dry. The two aft ports bled normally but just a trickle of fluid from the front port. I hooked up the aft ports to the brake lines then the front port bled normally. The brakes feel fine. I can count on one hand the number of brake master cylinders I've bled but I don't recall this nuance in the past.

Sixto
83 300SD

Probably had exhausted the source of fluid after drawing down the aft lines? Then you're getting an air pop?

I have only reduced the Master Cylinder of brake fluid, so as not to allow any air bubbles or air infiltration to the lines. With an archaic hand pump, I'd pull fluid through starting with the RT rear line to fresh looking colored fluid, left rear, RT frnt, then left frnt - NEVER allowing the freshly poured fluid to be diminished from eye sight in the Master Cylinder.

Don't know if this helps, but I take no chances with a dry line from the Master Cylinder.

The above was on my 83 300SD.

To be clear, I was bleeding a fresh master cylinder before attaching the brake lines. This was the master cylinder with all three ports dumping back into the reservoir. There was fluid in the forward compartment as far as I could see. The front port just wouldn't flow enough to bleed properly. Adding resistance to the rear ports got the front port flowing.

IIRC the FSM has a procedure for bench bleeding the master cylinder. It's not clear in the FSM whether a pressure bleeder will take care of a dry master cylinder, particularly in this car without ABS.

Sixto
83 300SD

Hi Sixto,

Cleaning my garage and found more parts for the 83 SD. Please give me a call.

Best,

Shane

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Shane83SD

The 2 aft ports are connected together, i.e. the MC serves as a "T" for the front brake tubing, so no surprise they both flowed. I don't know why your front port (rear brakes) didn't flow much. I replaced the MC on both my W123's and saw a healthy flow from both F & R systems. I "bench" bleed w/ MC on the car, using the pedal to push. If you were truly doing it on the bench, I suspect you weren't able to push hard enough to move the 2nd piston. There is a spring between the 2. I used plastic screw-in port fittings w/ thin clear tubing to return to the reservoir. Those came w/ the MC or I had from prior work. If your tube is larger it might provide less restriction, but doubt that matters since I have used steel 3/16" tubing on other cars w/ no issues.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Yup, I bled it in the car and I used plastic nipple fittings with clear hose back to the reservoir. After getting good flow the first time, the front port flowed like the aft two. It's somewhat reassuring that the front port feeds the rear brakes.

Sixto
83 300SD