I was replacing my brake fluid today and I let the rear run dry. I got just clean fluid at all bleeders but the pedal still bottoms out. I tried pumping the pedal and going over each wheel again. I was using a might vac and after going through 2 1/2 quarts of brake fluid, I still don't have any pedal.

With the MC empty I noticed some rust in the reservoir. Should I replace the Master Cylinder? Either way I think I need to bench bleed the master. If I buy a presure bleeder will that remove air from the MC or do I still have to bench bleed. Also can anyone think of any other problem that would make it so hard to bleed the brakes.

Thanks

 

you still need to bench bleed if it got air in there. A pressure bleeder will work better than a mighty vac, I could never get one of those to work very well.

 

I'm no brake expert, so this may not be 100% correct. When replacing only the master cylinder, it has to be bench bleed to remove any air. Then the old one is removed and the new one installed. The rest of the brake system is not bleed.

I had all fluid drained from my brake system: MC, all lines, and all calipers. The MC was off the car and I didn't bother to do a bench bleed on it. Filled up the master cylinder and pumped the pedal until no air bubble came out of it while watching it, had a helper. Once that was complete I then proceeded to bleed the lines and calipers. I bleed them until I could see no air in fluid when opening the bleeders on the calipers. I use one of those $5 bleeder kits with a clear plastic hose that allows me to view the fluid.
I have a full brake bedal. It does down about 1/3 way. If I use more foot power, I can lock up the tires and never get 1/2 way. I would say my brakes are as good if not better than the way it came from the factory.

Getting back to your issue. Did you have a good pedal before doing any work? If there is rust in the master cylinder, it possible that a piece of rust is affecting it. Even if you have a 'little' air in the system, the pedal should not go to the floor. Unless you can in point the problem, I would change the master cylinder. Re-bleed the entire system. Brake fluid is not expensive. However, if you can capture it and it is clean and clear, just re-use it. Normally a bad pedal indcate a bad master cylinder, air , or a leak. With a leak, you look for a wet area on the garage floor.

 

The brakes worked perfect before. This was just some preventive maintenance.

 

You don't want to push all that rust thru the whole brake system nor do you want to move the piston and seals with rusty fluid.

-Empty the resevoir
-Diconnect the brake lines from master cyl.
-Put temporary fittings and tubes if available onto master cyl
- use a small acid brush to stir up the sediment in the reservoir, then fill with clean fluid and use mytivac to flush out master. Do front and back until you get clear fluid
-reconnect brake lines and preferrably get pressure bleeder for the rest of the car. With a pressure bleeder, you need not bench bleed. A PB will spoil you.

Flushing the system once a year is a good idea and can prevent premature failures.
Google and you can make your own pressure bleeder. Most people have all the parts.

 

A remanned M/C is $35 at Autozone. Just replace the danged thing.