I have difficulties getting the air out the brake system after I had to “repair” two wheel cylinders that were leaking.
The pedal remains spongy and I can push almost to the floor.
The car slows down decently and remains straight but I cannot make the wheels to lock.
I have rigged a foot air pump to the reservoir and applied about 20psi pressure to the reservoir while bleeding the air out. But there is not much improvement to the stroke of the pedal or the sponginess.
After 3 pedal pumping strokes I did not see any air bubbles coming out.
The instruction book says that about 10 or 15 full pumping strokes of the pedal will be needed to get the air out of one wheel cylinder.
Knowing that the reservoir has to be refilled after 3 strokes this seems to be very cumbersome to get to 10-15 strokes per wheel cylinder.
Could it be that I really need to go to so many strokes per wheel cylinder in spite of putting backpressure to the reservoir?
Or could it be that the cups of the master cylinder are worn in such a way that the master cylinder looses its pressure somewhat?
Any other experience and suggestions?
Thank you very much.
Rik

Rik...I know what you mean about bleeding brakes. They seem to never get bled. You could try a Mityvac (vacuum pump) on the wheel cylinders. I have done it on my '31 Plymouth. Sometimes the person depressing the pedal in the car might let it up slightly allowing some air to be brought back in. I have never heard of putting air pressure on the master cylinder to push fluid through.

Harry, As the main cylinder and reservoir is practically at the same hight of the wheel cylinders of the Chrysler I assumed that air bubbles could remain in the main cylinder. Modern cars have the reservoir at least one foot above the main and wheel cylinder. That must provide a little pressure (12 inches watercolum) which should help remove the air bubbles better from the main cylinder. So the thought about putting pressure on the reservoir was ment to compensate for the lack of hight difference between the reservoir. ( I put 20psi or 150 inches of watercolum assuming that the system is used to such kind of pressures)
Since it did not help much I begin to suspect the main cylinder itself. I have never dismantled a main cylinder but I assume that things can wear there too in which case less pressure would go to the wheels.
Vacuum is another good idea though.
Thanks for the thought.
Anybody knowing how to diagnose a suspect main cylinder without dismantling it?
Rik

May also try pinching off the flex hoses and seeing if the brake pressure comes up, if so you can figure out which wheel cylinder has air, or you may also have to adjust the clearance of the shoes as well...or a combo of both..

Your reservoir should not run dry after only 3 pumps of the pedal. Something is wrong if it does. 10, 15 or more is normal. Otherwise the fluid would run out and leave you with no brakes as the shoes wore down.

Sometimes the brakes seem to be completely bled out but there is a bubble back in the line someplace.

Also air can get dissolved in the fluid while you are filling and bleeding the brakes. Let the car sit overnight and the air turns into bubbles that can be bled out.

I suggest you first, figure out why the master cylinder is running dry so fast. Then, bleed the brakes thoroughly without letting the master cylinder run dry. If you get air in the master cylinder you have to start all over and bleed the brakes again.

I had the main cylinder dismantled because I wanted to check whether the reason for the "sponginess" could be due to worn cups. They looked somewhat used so I replaced the cups but the sponginess remains after bleeding. Maybe the bleeding was not complete yet, so I will continue on Thursday.
This gave me the occasion to measure the content of the reservoir and to approximate the oil consumption per stroke.
The reservoir is about 6.3 cuinch.
The cylinder diameter is about 11/4 inch so the consumption per inch of cylinder stroke is 1,22 cuinch.
4 full pedal strokes with an open wheel cylinder bleed nearly drains the reservoir. So that's about 1.5 cuinch per travel.
To avoid risking to empty de reservoir I limit myself to 3 pumps of the pedal before refilling.
As you say that 10-15 pumps is more normal, could it be that I open the wheel cylinder bleed valve(s) too much during the bleeding process?
I can think of no other reason. I took the drums of a second time but could see no leaks.

I finally went to my Volkswagen /Audi garage for help.
They to my surprise had a standard issue tool from Volkswagen/Audi, which allows them to bleed the air out of brake systems under pressure. Similar to my foot pump system except that it allows for continuous brake oil replenishment.
It has a reservoir of DOT4 brake oil, an air pressure regulator and a flexible piping system with fittings of all sorts so that they can adapt to almost any brake system reservoir.
The regulator holds the reservoir under a pressure of 15-20psi
while the piping system continuously replenishes the main cylinder reservoir of the car.
Now my brakes work normally. A brake test on their test bank was done to confirm.
Thanks to all who helped and advised.
Rik

Hi, As you well-initiated members can tell, Im new to this community. Since everyone is talking 'bleeding' brakes, thought someone could send me in the right direction. Im looking to buy 1928 Buick - Im sure it has mechanical brakes - would want to convert to (at least ...) drum brakes. But want to keep the current wheel and tire configuration (original wooden spoke type) Would appreciate someone's response.

Thanks for your time,

Ron Zm