Bench bleeding master cylinder - still a bit confused

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62Ranchero200
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Bench bleeding master cylinder - still a bit confused

Post #1 by 62Ranchero200 » Sun Aug 21, 2016 12:01 pm

Greetings Ford Six Fans,

'62 Ranchero - originally 170, "three on the tree", 7.25" rear end, manual drum brakes all around, "fruit jar" single-chamber master cylinder.

I've already switched out to an 8" rear end with larger drum brakes; all brake hardware in the rear is new as of fall 2015, and only has a few hundred miles on it since.

I've already switched out the front brakes to disc; all brake hardware in the front is new as of New Years, and only has a few hundred miles on it since.

Still have the "fruit jar" single-chamber master cylinder and about to change it out. Have been reading about bench bleeding ... plumbing the new master cylinder outlets with adapter fittings and hoses, leaving the top off the master cylinder, and using the push rod to force air out of the master cylinder into the brake fluid inside, where it bubbles up to the top. I understand this process, but ...

I assume that no one installs the master cylinder to the car with the top off, but still full of brake fluid and with the bench bleeder kit installed. If you drain the master cylinder completely, you've negated the bench bleeding, right? There's air in the master cylinder again. So it seems to me that to preserve the bench bleeding and keep the air out of the master cylinder, you'd have to install plugs on the master cylinder outlets, leave the brake fluid inside and install it with the top on.

First question - are inverted flare plugs made? Those would not be commonly used in OE applications - why would Ford create a fitting, then plug it? If inverted flare plugs are not made, does something else work to keep the brake fluid from leaking out of the master cylinder without damaging the threads on the master cylinder outlets? If so, you'd have to remove the bench bleeder fitting quickly, hold your finger over the master cylinder outlet, then insert and tighten the plug. Is that what the bench bleeders do?

Likewise, once the master cylinder is installed in the car and the brake lines are ready to pickup, again you'd have to quickly remove the plugs, hold your finger over the master cylinder outlet, then insert and tighten the brake line fitting. Is that what bench bleeders do? Brake fluid is an excellent paint remover, so if any significant volume of brake fluid leaks out, it's going to remove the paint from the frame, firewall, steering gearbox, etc.

Maybe I'm just being dense about this. Wouldn't be the first time.

Thanks,
Bob
62 Ranchero, 252 cid, 300 rods, RaceTek pstns, ARP mains bolts & studs, balanced & blueprinted, CI AL head, 1.6 adj rckrs, Smith Bros, 274/274/108 cam, CI int, Holley 500, DSII, CI SS hdrs, PowerMaster strtr and 1wire alt, Optima, V8 rad, T-5z, 10" organic clutch, 5 lug 8" w/3.80 Trac Loc, rear drums, front 5 lug discs, Centerlines. Next: ?.

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B RON CO
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Re: Bench bleeding master cylinder - still a bit confused

Post #2 by B RON CO » Sun Aug 21, 2016 3:08 pm

Hi, if you are careful you won't lose to much brake fluid going from the bench vise to the car. Don't fill the master to the top before you install it. I do it the messy way, by pushing in the plunger and then covering the holes with two fingers as I release it. The brake fluid will squirt a couple of feet. You can do the lines before you mount it on the car. If the pedal is spongy you will have to bleed all the brake lines. Good luck
B RON CO. Still workin' on it!

1933 Ford Pickup - 59A Flathead V8
1966 Ford Bronco - U14 - 170/200 Straight 6
1966 Ford Mustang - 289 V8

mustang6
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Re: Bench bleeding master cylinder - still a bit confused

Post #3 by mustang6 » Sun Aug 21, 2016 5:03 pm

Often times new master cylinders come with plastic flare plugs in the holes, so I had saved and reused those over the years. Even if you plug them with a small rubber or plastic plug to help keep them from dripping that's all you need to do.

Also, I feel bench bleeding is really to "prime" the cylinder and get most of the air out, so after priming and before installation I put the plugs in, pour most of the fluid out of the top, put the cap back on, install it, take out the plugs, install the lines, take off the cap and top off the fluid. Any air that gets in during that process can just bleed out the wheel cylinders when I am doing those. If the cylinder is "primed" you will have no problems doing that. If you didn't bench bleed it at all you might have a time getting it to "prime" in the car.

Scott
Scott

68 Mustang 200 ci, Aussie 250-2V head, Dual Headers, Comp Cams 252H, DSII w/MSD 6AL, T-5, V8 suspension.

65 Ranchero 200 ci, late 170 head, Autolite 1101, 3.03 3 speed, Maverick 8" 4 lug rear with 3.55 gears.

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Re: Bench bleeding master cylinder - still a bit confused

Post #4 by B RON CO » Sun Aug 21, 2016 6:07 pm

PS be very careful not to get brake fluid on your paint job, and that means touching things with your hands after they got brake fluid on them. Good luck
B RON CO. Still workin' on it!

1933 Ford Pickup - 59A Flathead V8
1966 Ford Bronco - U14 - 170/200 Straight 6
1966 Ford Mustang - 289 V8

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