Upgrade from single master to vacuum boost dual master - 63 C20

[Asshat]

On the advice of many here, I would like to upgrade the master cylinder. It still has drum brakes- hope that is not an issue.

Can I just buy a dual master and booster from Rock Auto or is the Truck Shop better? Isn’t there a special bracket I need from Captain Fab?

[Captainfab]

For what you are doing I would recommend a booster and master assembly for a '67-'70 C20. Yes it will bolt up to my '63-'66 standard booster bracket.

[Asshat]

Originally Posted by Captainfab

For what you are doing I would recommend a booster and master assembly for a '67-'70 C20. Yes it will bolt up to my '63-'66 standard booster bracket.

Cool. How much for that bracket?

[Steeveedee]

Captain, do you sell the rest of the hydraulic stuff that he will need? Or can you point him to a source?

[LostMy65]

With a C20, you'll be happy with power drum brakes. And the dual master cylinder adds even more safety.

Here's a good thread from the FAQs:
http://67-72chevytrucks.com/vboard/s...d.php?t=332148

I also added one of these to the rear line so I could adjust for a loaded or unloaded bed. It's not necessary though.
https://www.summitracing.com/parts/s...BoCH9kQAvD_BwE

[Captainfab]

Originally Posted by Asshat

Cool. How much for that bracket?

The '63-'66 standard booster bracket is the same price as in post #1 of the for sale thread.

http://www.67-72chevytrucks.com/vboa...d.php?t=339081

Originally Posted by Steeveedee

Captain, do you sell the rest of the hydraulic stuff that he will need? Or can you point him to a source?

I don't see where the OP said anything about converting to a hydraulic clutch.

[Asshat]

Originally Posted by LostMy65

With a C20, you'll be happy with power drum brakes. And the dual master cylinder adds even more safety.

Here's a good thread from the FAQs:
http://67-72chevytrucks.com/vboard/s...d.php?t=332148

I also added one of these to the rear line so I could adjust for a loaded or unloaded bed. It's not necessary though.
https://www.summitracing.com/parts/s...BoCH9kQAvD_BwE

Hey - thanks for the link.
However, there are no pics showing up, probably since the thread is so old.

Bottom line, do just need to split the lines, so the front of the master goes to the front brakes, and the rear of the master goes to the back brakes?

[LostMy65]

Originally Posted by Asshat

Hey - thanks for the link.
However, there are no pics showing up, probably since the thread is so old.

Bottom line, do just need to split the lines, so the front of the master goes to the front brakes, and the rear of the master goes to the back brakes?

For some reason I thought the rear port went to the front brakes, but with drums it may not matter.
.
Also, I just went to the thread on my phone - the pics are there.
Here is part of the pics as screenshots starting from top to bottom.

[LostMy65]

I'm trying to post the rest, but I keep getting a security token issue message.
Give me a few.

[LostMy65]

Here's the rest.

[LostMy65]

Does that help?

[LostMy65]

Just found another thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=487384
And this one was in the FAQs:
http://67-72chevytrucks.com/vboard/s...d.php?t=599582

[Asshat]

Originally Posted by LostMy65

Does that help?

Yes, I will read through it.
Thank you.

It doesn’t show the booster, doesn’t make a difference, does it?

[Asshat]

Am I missing something? These write-ups just mention the splitting of lines and which master cyl to buy.

Should I just upgrade to the dual master and not worry about the Vacuum booster?

Will the dual master alone improve the braking?

[LostMy65]

I would do the booster while you are at it. I feel safer with the dual master cylinder, but I'm 55 and if I have to do a lot of braking on my 65, I definitely feel it in my right leg.

[Steeveedee]

Originally Posted by Asshat

Am I missing something? These write-ups just mention the splitting of lines and which master cyl to buy.

Should I just upgrade to the dual master and not worry about the Vacuum booster?

Will the dual master alone improve the braking?

The dual master gets you out of serious harm if front or rear brake fail, as you still have "half" the system to brake with. But it doesn't improve the braking itself. You'd need to go to disc brakes for that, and then I'd recommend power brakes.

[AcampoDave]

I run manual split system drums on one of my trucks and maual disc/drum on the other. Both stop great and take no more pedal pressure than a well maintained single pot system. I've never liked the look of the booster under the hood so I figured I'd go manual and if I felt like I ever needed to put in a booster I could always do it later. (That was at least 10 years ago and I still don't see a reason to add one). Either truck will lay a skid when I slam the pedal down and they don't stop much quicker than that. The truck with drums in front however, will start to fade under repeated use do to heat.
As far as tired knees go, I've had surgery in both of them and it's only the clutch that feels like a workout in heavy traffic. (More the muscles of the leg than the knee joint itself) Braking is no sweat. Remember though, I have half tons and have no experience with the heavier trucks.

[Asshat]

Those Impala master cylinders are not $20 anymore, more like $45 at O’Reilly.

[studeclunker]

Interesting thread and love the pics explaining the process. Wish I was so good at bending pipe!

Question:
Will the dual master bolt right up to my current booster that has a single master cylinder?
Do I have to completely replace the plumbing on my brakes, or can I just replace the lines to the distribution hub?

[Lugnutz65]

Here’s my contribution in 2 parts.

Part 1 is from my website and shows how I added the CaptainFab bracket and booster with dual MC for front disc brakes. LINK HERE.

Part 2 is a video I made when I still had drum/drum and converted to a dual MC.
VIDEO LINK HERE

[jayoldschool]

Originally Posted by Asshat

Those Impala master cylinders are not $20 anymore, more like $45 at O’Reilly.

Use an Impala master in a car. Put a 67 truck master in your truck ;-)

[Asshat]

Originally Posted by jayoldschool

Use an Impala master in a car. Put a 67 truck master in your truck ;-)

What do you do if the mounting holes are not inline horizontally? Mine are offset, one side is higher than the other.

[The Rocknrod]

Originally Posted by Asshat

What do you do if the mounting holes are not inline horizontally? Mine are offset, one side is higher than the other.

http://www.67-72chevytrucks.com/vboa...=1#post3257836

[theastronaut]

A booster is not neccessary if you do disc with pads that have a good compound and bite hard on their own. If you use ceramic pads that have a low coefficient of friction then it'll take excessive pedal pressure to make the truck stop with manual brakes. If you use a semi-metallic pad that has a more aggressive coefficient of friction it'll bite harder and stop easier with reasonable pedal pressure and not need a booster.

My problem with discs and a booster is that it can very easily have the problem of having too soft of a pedal, and modulating braking under emergency stop conditions becomes impossible.

These are just made up numbers and are extreme examples to prove a point, but lets say it takes ten pounds of pedal force to lock up the brakes, and nine pounds to stop as hard as possible without lockup. Can you vary the pedal pressure by only one pound to keep from skidding in an emergency stop situation? Or vary only one pound between 80% and 90% stopping ability? Thats really hard to do.

Then lets say a manual system locks up at 100 pounds, and max braking without lock up is 90 pounds of effort- you can more easily vary how much pressure you're applying to the pedal and stop as hard as possible without lock up because there's a wider range of pedal force needed between controllable braking and lock up.

The other issue I have with boosters is that some are overboosted so the pedal is very touchy and there's no feedback through the pedal. That makes braking accurately very hard.


My favorite setup was my old '66 with a CPP front disc kit with semi-metalic pads, rebuilt stock rear drums, and a non-power dual circuit master cylinder that was the same internal diameter as the original single circuit manual master cylinder. The smaller internal bore increases line pressure, which along with the disc made plenty of stopping power with reasonable pedal pressure and easy modulation of braking force needed to stop hard without locking up.


Issue number two... using tires that have a good compound and can actually stop harder without locking up as easily. More powerful brakes are pointless if you have a tire that is just going to skid.

[Lugnutz65]

The Astronaut,
Let’s see if you agree.
A smaller bore MC is less touchy because it pushes less fluid during the stroke compared to a larger bore making the same length stroke. Therefore a smaller bore MC is less sensitive or “touchy” than a larger bore MC.

Another method that can reduce the “touchy” feeling of boosted disc brakes is to drill a new hole where the pushrod connects to brake pedal arm. Most articles suggest moving the connection hole down 1”. Moving the pushrod down reduces the mechanical leverage from 9:1 to maybe 7.5 to 1.