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Any thoughts on why my brakes would fade to the floor?

The prior owner removed the booster from the circuit...


I rebuilt the master, booster and bled each line. I worked great for several weeks and now the pedal will go to the floor. No brake fluid at any of the connection points and fluid has not been topped off since I rebuilt them.

I am going to re-bleed the lines again (to make triple sure there is no air in the lines) but I thought I would ask to make sure I am not chasing a ghost.

Any chance the system or cylinders were cleaned with an incompatible cleaner that has deteriorated a rubber seal somewhere or water or some other contaminant has gotten into the brake fluid and is gassing and able to be compressed when the fluid temperature increases. As I recall, the brakes with the Hydrovac power unit need to be bled in stages and power unit done in a specific sequence. Any chance something was amiss in the bleeding?

What appears to be happening is that after the 1st push of the break pedal, the fluid drains backward into the fluid reservoir. Evidently that is why the break booster was bypassed--- I'm putting a 2lb residual valve in the system to stop the drain back.

Any issues by doing that?

There should be a residual (check) valve at the end of the master to prevent fluid draining back into the reservoir. When the brakes are applied the master cylinder piston moves a control piston in the booster to start the vacuum assist. The fluid from the master is also passed into the slave cylinder and brake lines to provide initial brake action. As the vacuum starts moving the power piston to apply more power another check valve in the power piston is supposed to trap the fluid in the slave cylinder so the vacuum assist is providing the power. Perhaps one or both of the valves are not working.

No idea of the specs for the master cylinder residual valve but probably 2-5psi. An external residual valve in the line between the master and booster might do the job if the master valve has failed or is missing. I would be careful to keep the valve at a low value so as not to provide so much valve resistance fluid could not easily return to the master and reservoir via spring pressure from the wheels when brakes are released. If not enough fluid is returned brakes would be a candidate for locking up or being extremely sensitive as they were repeatedly applied, each time adding more fluid and filling lines and wheel cylinders.

Here are a couple of scans from the 56 Stude manual. Your 57 Clipper was a facelifted 56 President model so brakes should be the same as the Stude manual details.

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Excellent. That is great. I will try that!

There is complete manual for 56 Studebaker and 57 Clipper supplement here on Packard info

Interesting issue...after redoing the bleeding a second time and having another mechanic do the same thing ALL by the book. We still came up with the same issue.

We needed to bleed the brakes the same way you would do a Duesenburg.

Thanks for all of the help and suggestions.

Gar

May I ask a question? This is sort of a followup to HH56's response in post #2. Is the bleeding being done exactly per the shop manual? The shop manual is very specific about several things. First, the power brake unit and the Hill Holder (if equipped) must be bled first before bleeding the wheel cylinders.

Second, manual bleeding (which I assume you are doing, as opposed to pressure bleeding) of the power brake unit is not quite intuitive. The power brake unit is bled by opening the bleeder valve first, then depressing the brake pedal, then closing the bleeder, and finally releasing the brake pedal. And, third, the engine should not be running, and there should be no vacuum in the power brake unit.

Very recently, some friends were bleeding the brakes on a Packard Hawk, and couldn't get the brakes to bleed correctly. When they consulted an old time Studebaker mechanic (not me, I'm just old ), they were told the same thing -- bleed the brakes exactly per the shop manual. The bleeding was then done per the shop manual, and the brakes bled fine.

This may not be your issue -- you may be very aware of the procedure for bleeding the power brake unit. But it's a good reminder for others who are not aware of the correct procedure.

I wanted to give a final update on my power brake issue.

I re-bled the power unit per the manual for a 3rd time, and I was able to get two tiny air bubbles out of the line. I did this by having the front end of the car elevated about 1" off of the ground.

Brakes work fine now and stop the car as expected.


++I appreciate all of the help and suggestions++

I wanted to give a final update on my power brake issue.

I re-bled the power unit per the manual for a 3rd time, and I was able to get two tiny air bubbles out of the line. I did this by having the front end of the car elevated about 1" off of the ground.

Brakes work fine now and stop the car as expected.


++I appreciate all of the help and suggestions++