Brake Lines Confusion

[ThreeQuarter]

I've searched for threads about this topic and I haven't found any that directly address my situation, so I'm reaching out for advice. Obviously I have some bending left to do to make these lines mate to the pressure switch, but here's my situation with the fit-up:

Equipment:
- 1968 C10 with original drum brakes
- All new Inline Tube SS line kit
- CPP Corvette-style master cylinder
- Original pressure switch from this drum/drum system, has two different fitting sizes

Installation details:
- Original pressure switch mounts perfectly to master cylinder with new Inline Tube lines. Mounts in same place with same orientation--small fitting forward and larger fitting to rear.
- Rear brake line at pressure switch has larger fitting
- Front brake line at pressure switch has smaller fitting

So, if I put the brake line fittings into the pressure switch ports where they naturally fit, I'll be violating the consensus advice here that says the the front brake line belongs in the rear port of the MC/pressure switch, and vice-versa.

Does that mean I need to adapt both line fittings to make the brake lines fit the correct ports, or is there something I'm missing?

[FirstOwner69]

I have a '69 3/4 ton with original drums. The rear port on the distribution block serves the rear brakes. From what I've read on here, on the disc brake trucks ('71s and '72s which had proportioning valves rather than distribution blocks) the front brakes attach to the rear port on the proportioning valve.

Somebody please correct me if I am wrong.

[Andy4639]

You are doing a Drum to Drum it shouldn't matter which line goes where. The distribution block is only to keep the system separated in case one side ruptures so the other side will keep pressure to stop you.
So either or are fine.
On a Disc to drum yes it's as you stated. But it's also to just separate the two lines. On a disc/drum master the rear bowl is bigger for the disc brakes up front require more fluid as the pads where down to keep them tight as the drum don't need as much so you have a smaller bowl. The reason for the disc bowl to be the rear is it applies the front brakes first when you push the pedal and then the rear drums.

[ThreeQuarter]

Perfect, thanks Andy. That will simplify things if it doesn't matter which port the drum/drum lines go to.

[70STOVEBOLT]

My disc/drum master cylinder has the large reservoir at the front and the front brake line is plumbed into the bottom of the prop valve.

[Andy4639]

Here is a good explanation of lines and how to hook them up.

https://static.summitracing.com/glob.../ssb-a0730.pdf



2) Connect the front brake outlet of the master cylinder to the port marked "F I" on the top of the
Prop Block. The outlet of the master cylinder for the front brakes will typically be the one for the
larger reservoir. If the reservoirs are the same size, a good rule of thumb is that the front
reservoir feeds the front brakes with GM master cylinders, while the rear reservoir feeds the front
brakes on Ford and Mopar master cylinders.
3) Next connect the two ports marked "F O" on the front and bottom of the Prop Block to the lines
feeding the front brakes of the vehicle. Most vehicles will have two separate brake lines: one
feeding the left (driver) front wheel and one feeding the right (passenger) front. If your vehicle
uses only one front brake line to feed both wheels, it is acceptable to plug the remaining front
outlet port of the Prop Block.
4) Connect the rear brake outlet port of the master cylinder to the port marked "R I" on the top of
the Prop Block.
5) Connect the port marked "R O" on the back of the Prop Block to the line feeding the rear brakes.
If your vehicle is equipped with a 1/4" rear brake line, use the supplied adapter fitting to connect
the line to the outlet of the prop block. SSBC has supplied the 1/4" adapter for the most popular
sizes. In the event that this fitting will not fit your line, you will need to locate a fitting from your
local parts store.
6) Tighten all fittings using a tube wrench and be sure to check for any leaks after the brake system
is bleed.

[Steeveedee]

Putting a Corvette style master cylinder on a truck is a mistake. There is a reason that that master cylinder isn't on a truck. You need to get the proper part number components and plumbing right for maximum brake safety. God help you if you get in a wreck and the suing party finds out that you have modified brakes. I see this all the time, and not just with trucks. Sorry to seem hard boiled about it, but brakes have to work properly, because people's lives depend on that.

[ThreeQuarter]

Originally Posted by Steeveedee

Putting a Corvette style master cylinder on a truck is a mistake. There is a reason that that master cylinder isn't on a truck. You need to get the proper part number components and plumbing right for maximum brake safety. God help you if you get in a wreck and the suing party finds out that you have modified brakes. I see this all the time, and not just with trucks. Sorry to seem hard boiled about it, but brakes have to work properly, because people's lives depend on that.

Steeveedee, do go on. I’m open to swapping this MC out for another. For my benefit, can you explain how this combo is more likely to lead to a failure compared to a factory MC?

[70STOVEBOLT]

If you use a Corvette master cylinder, you need to have front and rear disc brakes, as that is what it is designed for.

[AussieinNC]

Originally Posted by ThreeQuarter

Steeveedee, do go on. I’m open to swapping this MC out for another. For my benefit, can you explain how this combo is more likely to lead to a failure compared to a factory MC?

Before you proceed with fitting the lines etc, are you totally sure the "Corvette Style" master cylinder is suitable for Drum/Drum brake system? What part number is the master cylinder?

Most Corvette style masters are intended for Disk/Disk applications....Disk/Disk lack the residual line valves in the outlet ports essential for Drum/Drum systems. The residual line valves retain a small amount of line pressure to the wheel cylinders to prevent air intrusion into the systems from the wheel cylinder rubber cups.

Also, is this master cylinder being used on a power booster setup?

Please post part number of master cylinder and also if there is a booster in the system....

[Andy4639]

Dang I totally missed the CPP corvette part guy's.

This is not the right master cylinder for your truck. You need a drum/drum one. Why would you put a disc brake master on it in the first place knowing it's drums all around?

[ThreeQuarter]

I have a CPP Corvette STYLE master cylinder but it is (supposed to be) built for a drum/drum system. I bought it from Brothers as an assembly with the booster, because I wanted to be sure they were a complementary set, not a mismatch. The Brothers part number is KORN772.

I think the key word here is style. It’s a Corvette-style MC that is actually engineered for use with my factory drum brakes. All good then?

[Andy4639]

Originally Posted by ThreeQuarter

I have a CPP Corvette STYLE master cylinder but it is (supposed to be) built for a drum/drum system. I bought it from Brothers as an assembly with the booster, because I wanted to be sure they were a complementary set, not a mismatch. The Brothers part number is KORN772.

I think the key word here is style. It’s a Corvette-style MC that is actually engineered for use with my factory drum brakes. All good then?

OK, yea you should be fine then!
Man you had me worried there.

[RichardJ]

Bull ****, Bull ****, Bull ****, and more Bull ****.

There is no such thing as a Corvette type Master Cylinder.

Primary consideration for selecting a Master Cylinder is BORE DIAMETER.

It doesn't matter if it came from a Yugo , a Studebaker or a Corvette, as long as the BORE DIAMETER is correct for your vehicle.

Engineered for drums my arse. Let Chevy do your engineering.

Of secondary importance is the correct fitting size for the lines and the hole depth in the rear for manual or booster application. CPP provides a plug to insert in the piston hole to make their MC interchangeable between manual or power.

The reservoir size has little to do with the operation of the brake system. Larger reservoirs for Disc reserve capacity in Disc/Drum systems in the '70s & '80s have for the most part been replaced with single reservoirs with a electrical switch to signal low reserve fluid level.

The only reason for the larger disc reserve capacity is so the disc pads wear out BEFORE the reserve capacity was used up and emptied 50k miles down the road depending how hard you are on your brakes.

If you are replacing a MC on an original drum/drum system you want a MC with the same bore diameter that Chevy used originally.

If you are switching from original manual drum/drum to original power drum/drum you want a MC with the same bore diameter that Chevy used with power drum/drum.

Power systems usually use a slightly larger bore diameter than manual MC.
A larger bore diameter by itself requires greater pressure from your foot and that's where the booster comes in. The net result is the same hydraulic pressure coming out of the MC with less foot pressure.

One other thing that too many people fail to understand is that the pressure from the front MC port is exactly the same as the pressure from the rear MC port. If these two pressure are ever different, the Pressure Differential Switch shown in post#1 above will turn on the instrument panel Brake Light. The same switch is in the middle portion of a Combination Valve used with disc brake systems.

[ThreeQuarter]

RichardJ, thanks for the info. All the concepts you mentioned about brake system design ring true to me. Can you tell me: 1) What’s the bore diameter of my MC? and 2) What’s the bore diameter I am looking for?

[AussieinNC]

The "Corvette Style" is an advertising description only it seems IMO....

CPP lists both a 1" and a 15/16" bore master cylinder....

On the Brothers site so long as you selected Drum/Drum from the Size Color drop box you should be ok....

You can check for residual line valves by GENTLY probing inside the outlet ports on the master cylinder...use a small rounded nose piece of wire and probe gently....you should feel a small rubber style valve just inside the fitting in the port of the master cylinder...if the probe goes in more that 1/4" the line valve is most likely not there...check you original receipt and call Brothers to double check you have correct master...

In your original post the pic showing the distribution block simply needs to be turned around the get the posts aligned with the correct size pipe ends...

Hope this helps...

[ThreeQuarter]

Originally Posted by AussieinNC

The "Corvette Style" is an advertising description only it seems IMO....

CPP lists both a 1" and a 15/16" bore master cylinder....

On the Brothers site so long as you selected Drum/Drum from the Size Color drop box you should be ok....

Thanks, Aussie! I agree that “Corvette-style” refers to the cast that was used, but doesn’t necessarily mean the MC is machined to be used on a Vette. I’ve been assuming this all along, but didn’t have the knowledge of how I could verify it. I’ll do my best to check into this and will report back.