In my 1979 240D, I have this issue where the pedal goes almost to the floor when I first go to drive it in the morning. After a few stops, it's working fine and works fine for the rest of the day, but the next morning, the same issue occurs. The master cylinder and RF caliper sat dry for a while, so I'm wondering one of them is leaking. I'm going to check them, but is there anything else I should be looking at?

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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

I had a similar thing happen. I could not find a leak anywhere. I changed the master cylinder and that fixed it. I am not sure if the calipers can leak internally and fail. I am mostly sure the master can.
Be ready to pump the brakes if it happens when you actually need to stop. It happened to me on the freeway. Never trust an iffy system. If it happened once it will again. Possibly at anytime.

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Chris
84 280sl
82 300d euro

Remember to take a look at the booster, too. Sometimes they can come and go.

Dan

Bleed (either gravity method or conventional "pump" method) the left front caliper. If any air has entered the system that is where it is.

This is not a "fix", simply a test to check for air entering the system. It won't show where air is entering the system just the fact it is.

It is not unusual for small air bubbles to form after the system being open (as you said the master and one caliper was "dry") and then put back in service. The small bubbles will be pushed to the path of least resistance (shortest brake line) over the course of normal operation. The hydraulic system is designed to be "sealed" and won't vent the trapped air. Eventually the bubbles congregate and create a bubble large enough to interfere with proper fluid pressure.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Thumbs up Mike D ,

Thanks for the advice! My one question is, why would the air stop affecting the pedal once I've pressed the pedal once or twice at the beginning of the day? I would think that a low pedal caused by air would manifest itself consistently throughout the day, not only a couple times after the cars has been sitting after an extended length of time.

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Yup, sounds like fun . I've parked the car until I figure it out specifically because I don't want to experience that... fortunately, I can borrow my parents' car in situations like this, since my mom never drives but they have 2 cars.
I will! Thanks.

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."