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Brakes go to floor initially, then as pumped the pedal stays higher and firmer to the point brake feels good. If pressure is kept on pedal, brakes stay firm and pedal high. But once pedal let go, 20 seconds later pedal goes to floor again until pumped. Plenty of fluid, did system bleed including two on hydrovac (tandem piston cylinder style). Lines look good, not losing fluid. Any ideas why brake is soft before pumped?

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Did you bleed system before starting engine? I have heard bad tales about bleeding while running, so I always left engine off till all the air was gone. A vacuum pump is right handy for this job.  

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Lots of air gets trapped in those systems, in all reality vacuum bleeding it the best and quickest way. Otherwise you just need to spend a lot of time going back to bleed it. Air is usually in the secondary part of the booster system.

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On pickup trucks, if I replace the line along the frame heading to the rear axle I've found I usually have to pump some fluid through it before hooking it up to the rear axle line, otherwise it holds too much air and doesn't like to bleed for me. Likely because for a while I didn't have all the right tools. Now I have that cup with the tube that hooks to the bleeder valve. That thing is real handy for bleeding brakes.

Just don't let brake fluid get on paint, it eats through and destroys paint pretty quick.

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I've always filled all reservoirs on an empty system and bleed the master first to the inlet of the hydravac unit. Then bleed hydravac unit, then move to the wheel ends. Trying to bleed the system as a single unit leaves too many variables and guessing. Break the overall system into components and work it from that angle.

Vacuum is much easier if you have access to the process but it goes pretty quick with a couple of folks working in unison.

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Did bleed per manual in correct order. Did it manually and it does recommend pressure bleeding. Thinking of picking up a motive power bleeder and giving a try

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Leak in master, once past 10 psi on power bleeder the master cylinder started leaking. The more pressure the worse it got. Guess I’ll be looking for a new one or trying to rebuild it.

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If anyone looking for master and there’s is a wagner casting, give them a call. They looked up truck and were able to find what master cylinder needed. Turned out to be MC2842, still in production and readily available all over online. Never been the case on this rig in last 5 years, guess first for everything 

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