Master Cylinder Problem

[xpensivewino]

I have replaced all the components on my 69E brakes. Front and rear calipers are rebuilt. New ATE master cylinder, new lines and pipes. I am having trouble getting any pedal at all. I've gravity bled, pressure bled, and two man bled. When bleeding the rears, I get about half a pedal and normal pressure release upon cracking the bleeders. As soon as I transition to the front right and crack that bleeder, the pedal goes to the floor and does not return again. At this point it also trips the reset switch on the master it's self. It seems that the rear circuit is working but the front circuit is not pressurizing. I cracked the front and rear feed lines at the master it's self and I am getting fluid from both. So is it possible that the new out of the box ATE master is bad? Is there a for sure procedure to test this fact? I don't believe it is that the pistons aren't extending enough, as that is usually the cause of a soft pedal after a rebuild, but not the cause of getting no pedal at all. Any advice on this would help. Thanks Steve

[Orange71S]

Wino,
When I restored my 71 S, I had a problem keeping pressure in the brake lines. Whenever I would sit at a stoplight on an incline or hill, pressure would slowly melt away and the brake pedal would travel towards the floor.
I assumed I had done something wrong, because (like you), everything was brand new. I called the guys who rebuilt the calipers and asked them what they thought the issue was. They recommended replacing the master cylinder. I replaced it and the problem was solved.

So....yes.....brand new ATE master cylinders are sometimes defective out of the box.
My local wrench has also had similar experiences.
Jay

[xpensivewino]

Thank you Jay for the input. Very frustrating

[76911S]

Have you tried cracking the line at the front calipers? If no fluid there then move backward in the lines to see how far it is getting. You may have some junk in the lines unless you replace all of them as well. But it does sound like a master problem, maybe a piece of debris in the master is clogging it, I have seen that on a new master.

Mark..

[xpensivewino]

Everything is new, there is fluid at all four corners, just no pressure building. I cracked the lines at the master, and there is fluid at both the front and rear circuit ports. I'm ordering a new master today. It's such a basic system, that it can really only be a problem with the master. I may attempt to dissect the current one to determine what happened, or I may just shoot it with my 12 gauge and call it a day.

[Orval_F]

You can try the aircraft method of forcing fluid from the wheel cylinders back through the system to the master cylinder.

[76911S]

Well, okay. But you did not state if you are getting fluid to the front calipers? Just that there is fluid at the lines to the master. Another good bleed method is to attach a long piece of clear hose to a bleeder and attach the other end to a standing pole of some sort. Make sure the open end is above the fluid res height, crack open the bleeder and let it sit. Fluid will always find it's own level, so if it flowing through the system it will show up in the hose.

Did you make sure hard lines and hoses where clear before install? They can have crap in them.

Mark..

[mac73s]

+ 1 on a new ATE cylinder (from Porsche) being bad. Had the identical issue when finishing up the resto on my 70-S. My SOP is to replace all such parts even thought the existing master cylinder was working fine. Finally gave up after trying every bleeding method there is, reinstalled the original master cylinder and it bled fine with a nice firm pedal in about 15 minutes of effort. I returned the defective unit to Porsche and they replaced it, but it remains on the shelf...keeping the perfectly good (used one) in use for the time being.

[sithot]

Once had problems with some rebuilt brakes which was fixed by removing the pads and allowing the pistons to extend further. This forced the rubber seals to "bloom", meaning they unfolded completely. After that everything worked just fine.

Thanks to my old pal, Dick Hyland, for the tip.

[xpensivewino]

mac73S, I think you are right on the money. I do have fluid at all four calipers, and did a "gravity" bleed so it's not a case of poor bleeding skills. This is a case of no hydraulic pressure to the front calipers. I suspect that the issue sithot refers to will solve an unusually mushy pedal, but not a zero pressure instance. I have a new master, and will install and report. Thanks guys for all the input thus far...