Has anyone experienced this problem? Going by the manual , it states you depress the brake pedal fully while bleeding but what I’m finding is that allows the piston seal(rear seal) to travel past the rear port in the reservoir and leak out the rear of the m/cyl into the booster. I am thinking I have to put a block under the pedal to limit the stroke which should allow me to bleed the brakes. I’ve bled a lot of vehicle brakes before and only went to the manual after having this problem thinking it might say it needs to be blocked while bleeding only to read the above. It all started with a split in the brass T peice in the outlet needing to be changed, I can sort it , but had never experienced a M/cyl that could be overstroked. It obviously can’t happen with the brakes adjusted properly and bled up only needing minimal travel. What a bitch to bleed though manually.
I think you may want to look inside the master the overstroke?may have done something to the rear cup flipped or damaged
This right here would kind of put me in the frame of mind that maybe some previous repairs had not been done properly. It might be a good idea to have a '64 T-Bird service manual at your disposal. I would make no assumptions that the car has had any correct replacement parts installed by any number of previous owners. Or that they followed any special service procedures described in the Ford service manual.
My thought is that when the brakes failed; the master cylinder piston traveled into an area where it had not been in a long time and crossed over some corrosion which in turn damaged the outermost cup. Used to see this happen on off-road equipment when brought back on line after winter. No way is a master cylinder built to permit the intake port to become uncovered.
"No way is a master cylinder built to permit the intake port to become uncovered." So true, unless someone assembled the insides wrong, or left out parts. I would just buy a new correct for that year and make master cylinder and be done with it safely.
Thanks for your thoughts but, I have a factory manual I’m working to,and it instructions, This is an original 64 M/cyl, and all internals are as per the manual parts show, The seals are as per the manual except for the rear piston o/ring has been upgraded to a lip seal, The pushrod from the booster has been set as per the manual, 1” plus or minus a few thou from the mounting face, Once this is set and as the master is fit to the booster face, any movement from the piston can be seen though the makeup port in the reservoir so yes, this is set correctly, The brakes worked fine before I went to change the T peice, it’s only the bleeding of the brakes that the problem in the master cyl appeared. Measurements of the bore port depths( reservoir ports) and piston seal positions and travel all show the rear piston seal can travel past the makeup port, this cannot happen while the brake system is fully charged and the shoe adjustments are correct . All brake master cylinders I have worked on had a stop built into the piston forward of the front seal to stop over stroking( but these had side ports for the lines) , in this case none, like a wheel cylinder where the seals travel is only stopped by the fact the shoes contact the drums. I was just hoping to verify this with someone with experience on these master cylinders.
Just to add, today I measured how far the piston has to travel to get the rear seal to pass the makeup port and allow fluid to get behind the seal and enter the booster , 1.5”. And it can still travel deeper into the bore. I also measured the throw of the booster rod from the mounting face of the M/c with the brake pedal fully down and it’s 1.5” so it will in fact allow fluid to leak into the booster while bleeding the circuit. It won’t travel that far once bled and all brakes adjusted correctly though but at least I now know what the leakage was caused by. Next is to check if the brake peddle has a stop that is damaged or worn.
Sorted now , thanks for the comments. Put a block under the pedal to restrict the stroke, bled up perfectly. Just to add, this style M/c can be overstroked , as Ripley said, believe it or not!
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