Hot Rods Another master cylinder question

1953 Ford F100 -- I'm keeping the stock drum brakes but converting to a dual reservoir late 60's Ford drum/drum master cylinder. The port threads are 2 different sizes. I see a lot of discussion about which port goes to which end of the car, but this is mostly on disk/drum systems. Since it's drum/drum, no proportioning valve is needed. My thinking is that it doesn't matter which line goes to which port. Thoughts?

 

1/8 I’d run to the front. 1/4 I’d run to the rear. Chevy did it that way into 57 I know.

 

This is a good question.

 

Both ports are for 3/16" line, 3/16 inverted flare. Only the threads are sized differently on the two ports. This was obviously meant to allow the lines to only connect to specific ports in the OEM application. On the OEM application the master cylinder output goes through a differential pressure valve that illuminates an indicator lamp if there is a brake failure. I won't be using that valve, so either line could go to either port. I think I answered my own question.

 

The fitting suze on the MS isn’t designed for store bought size fittings only. Meaning the OE used deferent size fittings sometimes. To avoid unsightly adapters, I use the size fittings that fit the MS and the brake line. I plumbed mine with 3/16 lines. Removed the fittings from the parts store brake line and used the size that fits the MS
The parts store should have those. I sometimes clean and reuse the OE fittings.

 

I was able to source the correct inverted flare nuts so I won't have to use adapters. They're not only unsightly, but are another place to leak.

 

It makes no difference which way you hook them up

 

Seriously?

It most definitely determines which axle has the brakes applied first and the basic pressure applied to each axle.

According to this diagram of the distribution block on a 68 Mustang from a Mustang Forum the rear cylinder with the larger (1/2 inch threads) fitting goes to the front brakes while the front with the 3/8 fitting is for the rear brakes. That is on those particular Drum-Drum Ford Master cylinders though.

 

No prop valve being used

I added a 67 f100 to my 63 drums. No prop valve even though the 67 had one .
I think the the one closest to the firewall went to the front. Don’t quote me

both reservoirs were the same size. Drum/drum

 

Then how did GM get away with doing it the other way?

OP never said he was using a distribution block.

 

Yes seriously. If you actually took the time to read what he wrote there is no combination valve. You’re too busy trying to be the only one that knows anything.

Explain how it would make a difference on a drum drum master which way the lines are hooked up .

 

I used this MS in my merc.early 60s AMC
Interesting which one the manual the lines go to

haven’t located a similar diagram for an f100

 

How can it make a difference on which port to use on a drum-drum master cylinder? One word. TIMING.

No all mc are made this way but most have some built in bias to apply one port with pressure before the other. They can do this by changing the relationship between the seals and the port and also using internal valving. I would never just plumb whatever looked good without checking which port the manufacturer says to use for front and rear.

 

I have never seen any documentation or a master that has different spacing for the ports. I would welcome documentation that actually shows a difference in the vent port to primary seal spacing to apply one set at a different time. Doesn’t work that way, unless it’s a step bore master then it matters.

 

Timing of application is crucial for safe stopping. Get it backwards and you will have problems in a hard stop. The internal ports, springs, and cups are specific to each master cylinder. The Ford picture does show either port can be used for front or back depending on bore size and application, it doesn't mean they are interchangeable.

 

Strangely alot of masters have the firewall side/ flange side for the front brakes. Checking the original layout as stated above is key.

 

Take one apart and show where this “timing” takes place. I’m also interested to know where and how this timing happens with a single circuit master cylinder.

 

Single pots......
I don’t think timing is the correct term when it’s more like power.
The primaries on single pot systems are the front wheel cylinders , shoes and drums. If you’ll notice on nearly all vehicles the front brakes have larger wheel cylinders and wider drums and shoes.
This is how “brake bias” was accomplished on a single circuit system.
Another factor is adjustment.

 

I’ve always considered how the factory connected the lines whenever I swapped in a different master cylinder, just in case there is some factor, such as timing, designed in that I wasn’t aware of. I did the same if I used a factory distribution block. I’ve never had a problem.
It’s been a long, long time since I actually disassembled a conventional master cylinder and repaired it unless you count my unfortunate encounter with a Treadle-vac.

 

Yes and the same is true of a dual circuit, unless it’s a quick take up master they work exactly like two single pot masters, it’s strictly for safety, that’s why we have metering and proportioning valves.

 

Watch this animation for the 'timing' I was referring to.

The circuit that feeds the fronts (or builds pressure first) would depend on the design of the springs. So it would be good to refer to the OEM routing. If there is doubt pull the piston and spring stack out and see which spring compresses first (lower rate). This would indicate the front feed.

 

This ^^^^

 

Lots of good info and opinions here. Based on the referenced video, which line connects to which port depends on which circuit you want pressurized first, since pressure has to rise in the primary piston before the secondary piston is activated. I think it would usually be the front, but when using a master cylinder in a system outside of the OEM application, that could vary.

 

Not all master cyls

 

This gets debated regularly.
Port location isn’t the determining factor
If in doubt or worried on “timing” then bleed the MS, clean it up and see which port pumps fluid first.
there’s plenty where the front bowl(opposite the mounting flange) is plumbed to the front. Gm had a few
In the diagram I posted it can be either port depending on bore size.
I’d suggest if you wanted confirmation to look up the service info for the master cyl used.

 

It is milliseconds of a delay, unnoticeable in driving, everyone can believe what they wish. I am well aware of how they work, I have had hundreds apart and have a lot of publications on this stuff, not one reference to timing or applying first.

I hook them up according to reservoir size, if they are the same I hook them up so the lines are neat. Never had one not stop.

 

Every “why won’t my brakes work” thread no one gives a thought to piston/caliper/wheel cylinder size but we are up in arms about something that will make zero difference in brake performance.

 

So you are saying brake performance will not be affected by which end of the vehicle starts braking first ?

 

I spoke to a brake specialist about a similar issue a few years back. He told me " The larger reservoir is for the front disk brakes and the smaller for rear disks or drums. For a drum/drum setup, similar thinking. Front drums 'usually' have larger surface area than rear."
No end starts working before the other, just that the front has more pressure going to it.

 

Corrected my statement above... thx