Hot Rods Another master cylinder question

I’d like to build my dual drum as per the manual then drive it a while then swap the ports. Just out of curiosity.
I just follow the plumbing info from the OE.
I haven’t had any issue plumbing it that way.
I’ve used 2 Hydroboosts. Got the prop valve and booster from the junkyard, turn in the junkyard MS as a core and plumb it like the scrap vehicle was. Done. Did a single to dual MS swap on a 63. Plumbed it like the 67 f100. Done
Using willwood and other aftermarket brakes, I simply followed the instructions, called tech for questions.
Crap works great
I’m no brakeoligist

 

silly me...I always use a fruit jar single piston master cylinder on a drum drum set up and have a functioning ebrake
that and I make sure all my steering components are in good order....you loose your brakes you can steer into something to stop
loose your steering....oh wait...everybody has dual steering box setups now.....
but I also just made a non eventful 1000 mile round trip and drove in Denver/Colorado Springs traffic with mechanical brakes with multiple brake check occurrences...
carry on dual side mount brake masters.....

 

Now your putting words in my mouth, what I said is in a straight bore master cylinder neither end apply first or gets more pressure from the master.

I’m done now. I’ll go back to not trying to help with brakes.

 

Just because one port at the master gets fluid flowing first does not mean that circuit is stopping first. It still requires all four corners to become pressurized.

 

I agree with this logic. There is a steady-state amount of fluid in the lines, theory tells us that fluid is not compressible, aka no air in the system. There is enough residual pressure so any pressure to the pedal sends it out almost-instantaneously to the front and rear.

 

The ports don't matter, it's the reservoir size that matters. Since disc brake calipers take more fluid, and one part of the dual reservoirs is usually larger, I use the larger reservoir to feed the disc brakes. But if the reservoirs are equal size on a drum drum setup it wont matter which goes where. If they are different I'd still probably put the larger reservoir to feed the front drums since front brakes usually do more braking than rear.

 

It never ends here ...

There is also a factor called gravity. If the MC mounting position is below the wheel cylinder (or caliper) mounting level positions, the fluid will drain back and into the MC. That is one reason for a low/soft pedal.

And there is more than one reason/need for a RPV(s).

We now return you to the regular broadcasting ...

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I looked into this. I’m even bought the T shirt. It’s hanging in the closet.

It’s so simple right?
Right.

So I have my double cylinder. I need just a few fittings. How simple is that?
So I go to the NAPA......
I tell the counter guy what I’m doing and he is looking at me like I’m a cyclops or something.
A 1967 master in a ‘65????
Why would you want to do that?
I explain that.....
It’s for the children.

It’s not like the old days where you go through the drawers of fittings. Nope, each fitting is individually wrapped and tagged in it’s cute little baggy.

Apparently the Secret Service and Homeland Security has to be notified for me to go behind the counter to the fitting bin.
The counter guy is not happy? It’s really difficult to see if it’s the right fitting through a plastic bag.
I’m nice. I’m very respectful. I’m a little dumb too because I end up buying fittings for an ice maker.
Yep.......
An Ice Maker.........
He was so proud of those ice maker fittings and was very fatigued because he had to walk 10 feet and bend over and open a bin,
I felt obligated to buy a few dollars worth of ice maker fittings.
Who knows, maybe I’ll install me an ice maker one day.
The counter guy said that’s what all the farmers use on their tractors.
I never knew tractors had ice makers.
Who knew?
So.....
I go to Oreillys.
I must of had clearance because those kids let me go the bin.
They must have thought I was Fonzie or something. They were like heyyyy this old guy knows his stuff. Our fitting bin is yours.
So I find a T for the brake switch.

You have to know exactly what fitting you need down to the part number.
Guess what.....apparently basic fittings are being discontinued.
Not only that there’s the AN fitting bubble flair BS that’s not DOT
WTF??????
Then you get into the pedal ratio blah blah blah......
I come to the realization that.....

You know the old single pot worked.

The only reason that I’m going double cylinder is because of an internet guilt trip.

It’s the must do upgrade.
You’ll be sorrrrrrry! All that stuff.

I finally admit to myself that......
I like old cars.
I like drum brakes
I like single masters.
I like how they feel.
I like making that system as good as it can be.
I understand the limitations.
My cars are pretty much stock
I’m going to go with what I know.

So......
For me I’m staying stock.

If stock is not for you I completely understand.
Plan it
Research it
Find out exactly what you need.
Refer to what the factory did.

it’s not the old days anymore.
A brake system is not something you build on the fly or by the seat of yours pants.
There’s no maybe “maybe this will work”

You have to know your stuff and have your poop in a group.

If not, it’s better to stay stock.

 

https://www.jalopyjournal.com/forum/threads/fittings-pictures-to-determine-what-you-need.1315828/

 

F-one: Our old NAPA store got bought out by some kinda syndicate of young cats. Still NAPA, and the young guys try. Our old guy didn't like pulling out the old paper books, but at least he had them. For fittings, now they got this huge rack of the little drawers.......with not one scrap of useful information on the drawer. Just a number, doesn't even say whether inch or F*cking metric. Parts kid says, "welcome to my world."

 

I've downloaded the brass fitting catalogs -- Edelman, Gates, Weatherhead, etc., and figure out the part number I need and write it down on a slip of paper I can hand to the parts kid before I ever walk into the store. It makes life easier.

 

My impulses were once again influenced by flawed logic. Corrected logic applied in following posts.

I've always worked with the opposite assumption. Calipers may take more fluid to fill initially. But once filled, they take very little fluid to actuate. When the brakes are released the piston(s) barely move back into the caliper, just far enough to create an air-gap between the pads and the rotor. It takes very little fluid volume to then re-apply the brakes. For the most part I think that the reason the OEMs gravitated towards disk brakes was their simplicity and the lack of hardware needed to release them.

With drum brakes however, it may not take as much fluid to initially fill the wheel cylinders. But when released the shoe return springs have to pull back the brake shoes a pretty fair distance to clear the drum surface. Definitely further than a couple thousandths inch air-gap like the disk brakes. This displaces more fluid from the wheels cylinders which in turn requires an increased volume of brake fluid to re-apply the drum brakes.

If I had a master cylinder with one large and one small reservoir and a disk/drum brake system, my first impulse would be to plumb the large reservoir to the drum brakes and the small reservoir to the disk brakes. Has anyone else noticed this as a common pattern when working on OEM brake systems?

If it was a 4 wheel disk or 4 wheel drum vehicle I'd have to do a little more research so it didn't make my brain hurt.

 

I took my corvette style master cylinder to a local shop that is known for being the go to place for brake parts for fittings, they even had brakes in their name. They had no idea what they were looking at and were confused about the 2 different size fittings. I had to order from Amazon.

 

In answer to Claymart. How much brake fluid would the master cly, disk brake reservoir need if the pads are worn completely out and the caliper pistons extended almost all the way out in their bore ? That's why the disks have the large reservoir. A wheel cylinder has to fill approx a one inch bore with brake fluid , a brake caliper has to fill a 3 inch bore in most full size cars

 

My impulses were once again influenced by flawed logic. Corrected logic applied in following posts.

As pads and rotors and shoes and drums wear it will indeed take a bit more fluid to keep the calipers and wheel cylinders filled. That's why even if you don't see any leaks you still may have to occasionally top-up the brake fluid in the reservoir. I'm not aware that hydraulic brakes have ever been considered to be a "sealed system".

Either way it still takes only a relatively small volume of brake fluid to re-apply the brakes. Especially when drum brakes are kept properly adjusted and the self-adjusters are properly installed and maintained.

 

That impulse is going to get you hurt (or worse) and a very stretched seat cover.

 

My best luck with fittings is rooting around in the Ace Hardware bins, I just match up what I think will work. Tags and descriptions, most things are not in their OG bin locations. There is always an open-untagged one I use as a test piece.

 

My impulses were once again influenced by flawed logic. Corrected logic applied in following posts.

So you're saying that you've seen, on OEM brake systems, a regular pattern of the larger reservoir serving the front disc brakes and the smaller reservoir serving the rear drums? Do you see the same pattern on GM, Chrysler, Ford and other vehicle manufacturers?

 

No, I did not say that. Re-read your statement in that post.

 

When you treat the parts store people respectfully, they usually will let ya look thru things like fittings to get the correct stuff

 

They use a larger reservoir with disk brakes, because as the pads wear, the fluid moves to the calipers and stays there. Normal use makes the level go down, so the reservoir needs to hold enough fluid that it won't run dry before the pads wear out completely.

Drum brakes don't do this, they keep the same amount of fluid in the wheel cylinders, because the self adjusters (or the person adjusting the brakes) makes up for wear by moving the lower end of the shoes further apart.

If you understand why the engineers do things, then you can do it the right way yourself.

 

I usually ask the parts kids if they wanna learn something new today....they usually do and are amazed that old grey beards know about parts....and books made from trees.

When you have to drive to a parts store a significant distance, these things pay for themselves in a hurry.

https://www.nationaltoolwarehouse.c...3MRmNODhQQxvPlstyCk8QXX7KcCinqTBoCR78QAvD_BwE

 

Jim’s last statement says it all right there.

 

I've had to re-read things a couple more times but I'm seeing the logic in your conclusion. Thanks for pin-pointing just where my train of thought got derailed.

 

!!! BINGO !!!​

So, as the shoe pads wear, and the WC's have to push the shoes out further to contact the drum and the fluid level drops due to fluid displacement, there is no need to top off the drum brake reservoir of the MC? Was this also true with a four wheel drum SGL RESVR MC?

- CONFUSED IN W(BY GOD)V ...

 

Shoes are used with drum brakes. Pads are used with disc brakes.

Drum brakes have a stop for the shoe, so the shoe always ends up in the same place relative to the wheel cylinder, as the shoe wears. So the MC level will remain the same if there are no leaks.

 

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I think I'm beginning to understand how this scenario works.

It may help if you can imagine a drum brake system that either has no self-adjusters, non-functioning self-adjusters, or is never manually adjusted.

As the brake shoes wear, and if no adjustment is made for that wear, it will take consistently more fluid volume to move the shoes into contact with the drums. Keeping the shoes manually or self-adjusted compensates for that wear (by providing a variable stop for brake shoe return) and eliminates the need for additional fluid volume at the wheel cylinders.

Does it sound like I've got my brain wrapped around this the right way?

 

Not really.

The adjusters for brake drums spread the bottom of the shoes apart, to make up for wear. The tops of the shoes always retract to the stops, so the resting place of the wheel cylinder pistons is always the same.

If you don't keep drum brakes adjusted, then the pistons have to move farther when you apply the brakes, but they still always return to the same place, so the resting fluid level never goes down.

 

Let me try it this way. A brake shoe assembly is made from several components.

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1) WEB

2) LINING TABLE

3) BRAKE LINING or PAD

Yes, they will return to the stop unless there is a mechanical/hydraulic failure.

As the pads ... er sorry ... brake linings wear, it will require more fluid to move the shoes to fully contact the drum. As you periodically (hopefully) adjust the shoes (or have self-adjusting brakes) the lower shoe will also move closer to the drum.

So, if you never have to add fluid to compensate for the additional distance movement, where does the required additional fluid amount come from? Help me here, I cannot understand.

 

The extra fluid required has all ready been factored into the reservoir for “allowable” wear. Go beyond that, well that’s another thing all together.