Bench Bleed Master Cyl Question

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mitch340Duster

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Rebuilt my original Duster master which I had re-sleeved. (front disc / rear drum). I'm trying to bench bleed it but I get nothing from the front reservoir tube (the smaller reservoir that services the rear brakes). No air, no fluid. I'm definitely skeptical of the residual pressure check valve,which my FSM said to install in the "front" reservoir. Obviously a spring-loaded rubber plug sealing the port would prevent anything from flowing through it.
My gut tells me all is OK and it's just some weird design thing, but I wanted to ask about it before installing the master on the car. Thanks for your thoughts

DSCN2030.JPG
 
Rebuilt my original Duster master which I had re-sleeved. (front disc / rear drum). I'm trying to bench bleed it but I get nothing from the front reservoir tube (the smaller reservoir that services the rear brakes). No air, no fluid. I'm definitely skeptical of the residual pressure check valve,which my FSM said to install in the "front" reservoir. Obviously a spring-loaded rubber plug sealing the port would prevent anything from flowing through it.
My gut tells me all is OK and it's just some weird design thing, but I wanted to ask about it before installing the master on the car. Thanks for your thoughts

View attachment 1715376026

Try capping that tube with your finger tip on the return of the piston.
It will add suction and help the fluid pull into it.
I have had to do this with a few of them.
 
I just did this yesterday and it seemed like one reservoir bled much sooner than the other. It took a while pumping to get anything through the second.
 
Like TB says; you have to use your finger tips to act as valves, so the fluid doesn't just shuttle back and forth thru the compensating ports. You have to do this on the bench, cuz it will be far more difficult after installation, and probably messy, and, Dot-4 or less brake fluid eats paint.
The residual valves go in the lines that operate brake shoes. Lines to discs must not have them, else the pads will get cooked. In a factory Mopar, the frontmost reservoir gets plumbed to the rear brakes.
 
Thanks for all your time. Long story even longer since I'm taking a break before cleaning-up lots of brake fluid in the garage. Tried all of the above with no joy. Today, 1st thing, I decided to disassemble the master and start over. I just didn't like the way things "felt" yesterday. In-addition to the other problem the plunger was choppy and tight. First time I put it back together it was a little better, but still would not bleed the front reservoir. So I decided to install it on the car against AJ's advice so that I could have my angry wife pump the pedal while I stood guard against fluid spills. Still nothing, and no indication of any vacuum while doing the finger trick. Then I noticed that, when looking into the small holes on the bottom of the master, I could see the rear piston moving but not the front. Removed it again, disassembled it again. This time I ran some 1000 grit around the bore, cleaned and re-assembled. It felt better, and upon re-assembly I got some immediate satisfaction from the front reservoir. I dunno….I guess maybe the bore was just a little too tight and the front piston was getting hung. BTW AJ the reason for this job is because the master leaked fluid onto the firewall both inside and out, and ruined the paint on both sides below it. This occurred nearly 2 years ago and I have not had a window of time to take care of it until now. Not even a square foot of firewall had to be re-painted but you can imagine what a PITA it was to get to everything. Thanks again for your help !
 
So unbelievably I have another update on this. Cleaned the garage real nice today, psyched about finally installing the master. Tried a bench bleed and SAME S**T AGAIN. No fluid pumping from the front reservoir and tight, choppy operation. WTF ?? After much head-scratching and troubleshooting I found that the culprit is the stop / lock bolt that screws into the bottom of the master. When it's tight it's locking-up the front piston. If I remove it everything works fine. When it's installed everything still works but only until the bolt is tightened, then it locks the piston up. The only purpose I can see that this bolt serves is to keep the pistons from coming out of the bore, which would be a bad thing however there's also a plate at the rear of the master (that the bellows attaches to) that essentially serves the same purpose. The only solution I can come up with is that instead of grinding down the original stop bolt, which would have worked but I didn't want to destroy it in-case I need it again some day, I got a new 14/28 x 1/2 bolt, cut it down shorter, and installed it with an 0-ring. No, I'm not crazy about this solution but it's NOT gonna work any other way. Another weird thing is the rebuild kit came with a lock bolt that is completely different from the original. (smaller diameter and it has a long pin end). If you ever have 10 hours to kill you can find similar unexplainable situations that I have encountered when re-assembling this car.
 
what a pain. no wonder i don't rebuild them. i'd have the wheels chocked the first time i put it in gear
 
So unbelievably I have another update on this. Cleaned the garage real nice today, psyched about finally installing the master. Tried a bench bleed and SAME S**T AGAIN. No fluid pumping from the front reservoir and tight, choppy operation. WTF ?? After much head-scratching and troubleshooting I found that the culprit is the stop / lock bolt that screws into the bottom of the master. When it's tight it's locking-up the front piston. If I remove it everything works fine. When it's installed everything still works but only until the bolt is tightened, then it locks the piston up. The only purpose I can see that this bolt serves is to keep the pistons from coming out of the bore, which would be a bad thing however there's also a plate at the rear of the master (that the bellows attaches to) that essentially serves the same purpose. The only solution I can come up with is that instead of grinding down the original stop bolt, which would have worked but I didn't want to destroy it in-case I need it again some day, I got a new 14/28 x 1/2 bolt, cut it down shorter, and installed it with an 0-ring. No, I'm not crazy about this solution but it's NOT gonna work any other way. Another weird thing is the rebuild kit came with a lock bolt that is completely different from the original. (smaller diameter and it has a long pin end). If you ever have 10 hours to kill you can find similar unexplainable situations that I have encountered when re-assembling this car.

The tip of that bolt goes in a specific place to keep the front piston from returning too far.
It sounds like you had it on the piston instead.

This is a Ford master, but you can see how that bolt stops the front piston from returning further but allows it to go in to push fluid.
You have to push that front piston in a little against it's spring, then the stop bolt goes in.

h5613c.jpg
 
"That's it, I'm out". I was confident that the problem was "solved" by using an incorrect stop bolt, which I wasn't wild about doing anyhow, but even now the same issue re-appeared again. The master is pumping for the rear system, but with WAY less force than the front. Maybe normal, I don't know, but at one point I know it was pumping a lot more than it is now. I can see that the piston is moving, but only slightly. The investigation continues. I'm able to bleed the rear brakes, getting fluid from the wheel cylinders when bleeding, so I know it's pumping fluid, BUT I can still turn the rear wheels while my now angrier wife is again handling the brake pedal. Adjustment? I don't think so cuz there's normal drag on the wheels when turning them. So, I removed the brake drums and had her mash the pedal. If I remember correctly one time when I was a kid I forgot that the drums weren't on (not this car) and mashed the pedal, and it was dramatic, with shoes and springs and s**t flying everywhere. This time no such fun. All that's happening is only one of the shoes on each side is moving very slightly, but not nearly enough to provide braking.
I dunno, maybe the rebuild kit is not getting along with this master, maybe there's some issue with the re-sleeving. I found another correct master today that I ordered so I'll try that. This whole thing started 2 years ago and at that time there was not a correct master to be found anywhere, that's why I had the re-sleeve done, and if this wasn't enough, I stripped the threads on one of the coiled brake lines that go into the master. I wouldn't even have mentioned it except to give a shout-out to Nick at "FineLines". I bought all of the lines for this car from them. He didn't even have me in their system anymore since it was so long ago but still is sending me a replacement line for free. This kind of stuff is great to see in this hobby.
Again, thanks for everyone's help. I'll consider this thread closed with no definitive answer, but I'll report back after I install the next master.
 
If the master won't bench bleed, finger-valving the ports, then it's not likely to bleed on the car either.
My guess is the one chamber's compensating port is not open or restricted. The re-sleever should have drilled it out, but only very small. If it's too big, the fluid will just shuttle back and forth from reservoir to chamber. If it it's too small, you will have to wait between strokes, else any air in the bench-bleeding line will act like a big airspring, and fluid transfer into the chamber will be very slow.
Picture a syringe; when you pull fluid into it, the little air bubble at the bottom suddenly becomes a big bubble, as the fluid slowly enters the inlet. Then you flip the syringe upside down and eject the bubble, which has now returned to it's former size. On the next pull, the fluid enters a lil faster and you have to work harder to draw it in... cuz the airspring is gone.
Now drill out the hole in the bottom of the syringe.
And now when you draw in the fluid, it rushes in. The air bubble is still there but it doesn't grow to it's former size.
The M/C and Compensating port work in the same way, except you don't have to upend it to get the air out. But, and this is important, if the piston does not return to it's proper parking spot, then the compensating port does not open, and no fresh fluid can enter the chamber.
 
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