I replaced all the brake hoses on my Ranchero this weekend. While bleeding, I inadvertently let the master cylinder run dry.  The pedal was very soft, so today I rebled all four wheels and still have very little pedal. Can the master cylinder be damaged by letting it run dry? All brake fittings were dry this morning w/no leaks apparent. This is the original type master cylinder. Thanks for any help!

James

Possibly what has happened is this.Assumung its a master thats been in use for a long time the bore develops a wear area .When you bled the brakes the piston moves past the regular wear area and damages the rubber sealing cups.I dont recall for sure but is that master a single?You might come up with a kit which gives new cups and pistons.OR you might take this opportunity to switch to a newer dual master.Just my suggestion on what has happened.

  

Mark, thanks for the reply, it makes good sense. I do have a single master cylinder. I see ebay has a dual w/booster for my application offered regularly for $200. Has anyone used this and what would be the pitfalls?

you probly still have air in your lines.sometimes it takes several tries.

You may want to get a newer single M/C. Mustang,Granada etc non power brake . The brakes dont care what type of M/C sent the fluid to the shoe. May consider a dual cylinder. easy to install . I have 78 Granada dual cylinder in my bird.Didnt cost 200 either. I had the same problem with my install. It was just air and took several bleeds to remove it.

55Birdman  Hickory NC

As suggested before you replace it try bleeding again.I did mine recently.To work by yourself get a clean jar and a piece of hose to fit the bleeder screw.Fill the jar with enough clean  brake fluid and stick one end of hose in the fluid and open the bleeder and attach hose.Keep the master full and pump each line starting with longest.As  long as the hose is immersed you wont draw air back in.Close each line as you finish it.

  

Thanks for all the replies. I will try another bleeding or two before I replace the master cylinder.

If the front of the car is jacked up appreciably higher than the back, air may be trapped in the forward end of the master cyl and cannot be expelled into the line to be bled out, nor be able to come out of the feed hole in about the center of the bore.  Had that happen to me on a non Ford once.

John - "The Hoosier Hurricane"

If you ran the master cyl dry, I'd bleed it as well.....bleeding it via the wheel cylinders can take a while.  Just use the m/c output fitting as you would the wheel cylinder bleed valve----open and close as though it were a w/c bleeder.  Once you do that, then bleed the w/c's as you normally would. 

Almost a year ago I learned the value of bench bleeding.



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Lawrenceville, GA