Master Cylinder Help Please

[Luke87gt]

Hi guys, I’m hoping you can steer me to the best option master cylinder for my 1969 c10. I got drop spindles and will be doing the front disk conversion (keeping the rears stock drum)

First, I’d like to keep the brakes manual. I understand the the 4wheel drum brakes came with a 1.125” MC bore. With manual brakes, I will need 1” or 15/16” so the pedal isn’t too hard. Which of those two do you recommend and why?

Next, can you point me to a MC online that is a good option for me? I’m looking for something that’s good value and will bolt up to my truck and existing lines with as little modification as possible. If available on Rockauto, that’s a plus!

Lastly, I also need a proportioning valve. I see a lot of MCs being sold without these.

Thank you.

[72c20customcamper]

I believe the 71 trucks had an option to have non power assisted disc brakes . So a master cylinder for that year would work. You might have to get adapters for the lines at the portioning valve because I believe the lines are of different diameters . I got the two adapters from Napa .

[Luke87gt]

Strange, every MC Rockauto shows for the 71-72 is 1.125” bore. And RA doesn’t seem to sell proportioning valves…

Ideally there’s something out there that won’t require adapters and is plug and go for a ‘69.

I mean these are like the most popular classic truck of all time aren’t they, lol

[Luke87gt]

This looks like it could work…

https://www.speedwaymotors.com/GM-Co...BoCeQ8QAvD_BwE

[Luke87gt]

I would need a new proportioning valve

Another source of confusion, every MC for a 1969 on Rockauto shows 1” bore.

Why won’t that work for front disks?

[Steeveedee]

There are different guts in a disc brake master cylinder.

[Luke87gt]

Originally Posted by Steeveedee

There are different guts in a disc brake master cylinder.

You’re right Steevee, that’s the part I was ignoring.

[Luke87gt]

There’s also the option to get an adj prop valve… that would then go on the rear line only?

[Rust_never_sleeps]

https://mpbrakes.com/master-cylinder-sizing-guide/

[binford]

What luke posted was correct. I've used the corvette master cylinders before.
The 7/8 vs 1" is close. The 7/8" will require more pedel travel and feel like you have more power over 1" master cylinder. The larger the MC pistion the harder you have to push with manual brakes.

The differance between disc and drum brakes is the size of the pistion getting pushed. Disc brakes use a lager pistion and require more fluid to be pushed, so they need a MC larger pistion. Which is why they created "power brakes".

My 1968 was all manual. The only thing power was the engine, my MC was 7/8" for my truck with drums all the way around.

Question, do you have power steering?
My 71 has power steering with stock disc brakes. I just upgraded that to used hydro boost brakes from a newer chevy it has a 1 5/16 mc pistion. It uses the powersteering fluid to add assit to your brakes vs using vacumm. They work amazing.

[OL SKOOL]

Originally Posted by Rust_never_sleeps

https://mpbrakes.com/master-cylinder-sizing-guide/

Mr. Rust that is an excellent description of master cylinders and bore sizing applications thank you learned a lot.

[BRL]

I just wanna make a comment here that isn't much help to answer your question concerning master cylinder bore size but I had a 73 C-10 that had manual front disks and those were by far the best brakes I've ever had, including power assisted disks up front.

They were so controllable using just foot pressure that I would get the proverbial 9 cents change every time.

Someone T-boned the truck and I had it hauled off to the yard before I found out the brakes could have been easily modified to fit in my 69 C-10.

[Luke87gt]

Originally Posted by binford

What luke posted was correct. I've used the corvette master cylinders before.
The 7/8 vs 1" is close. The 7/8" will require more pedel travel and feel like you have more power over 1" master cylinder. The larger the MC pistion the harder you have to push with manual brakes.

The differance between disc and drum brakes is the size of the pistion getting pushed. Disc brakes use a lager pistion and require more fluid to be pushed, so they need a MC larger pistion. Which is why they created "power brakes".

My 1968 was all manual. The only thing power was the engine, my MC was 7/8" for my truck with drums all the way around.

Question, do you have power steering?
My 71 has power steering with stock disc brakes. I just upgraded that to used hydro boost brakes from a newer chevy it has a 1 5/16 mc pistion. It uses the powersteering fluid to add assit to your brakes vs using vacumm. They work amazing.

Thank you, how did the corvette 1” MC feel for you?

[425HP409]

Originally Posted by Luke87gt

This looks like it could work…

https://www.speedwaymotors.com/GM-Co...BoCeQ8QAvD_BwE

This master cylinder says in one place will work with disc/drum and drum/drum. In the more detailed description it says it will work with disc/drum. All Corvettes since the introduction of disc brakes in 1965 had 4 wheel disc brakes.

Master cylinders have a one way check valve in the outlet ports if it is for drum brakes. If it is for a disc/drum application it has the one way check valve only in the drum side. If it is for 4 wheel disc it does not have a check valve in the master cylinder, either port.
The one way check valve for drum brakes leaves a little pressure in the line to make up for the brakes shoes not touching the drums. This allows the brakes to contact the rotors and drums at about the same time. If you put a master cylinder on a disc setup with the check valve in place you will have the shoes always having pressure against the rotor, not good.

I put 4 wheel discs on my 68 and used a Corvette master cylinder because I knew it would not have check valves. I did the same when I put rear discs on my 77 GMC Sprint. They both work great.

[mike16]

70 t0 72 firebird came with non power disc brakes.

[theastronaut]

I used a 1" bore when I swapped to discs on the front of my '66 C10 and the pedal effort/feel is perfect. The pedal is firm, drops just the right amount to heel-toe downshift, and is very easy to modulate near lock up. Remember that *you* are the ABS system; the smaller the bore the easier it is to lock up the brakes and slide in a panic stop situation, so don't make the pedal too light/easy- you need to put some effort and thought into locking up the brakes.

The "proportioning valves" shown in the first reply is actually a "combination valve" which includes a hold off/metering valve for the front discs and a prop valve in the rear, but who knows what its calibrated for which is why I went with separate valves and an adjustable proportioning valve. That way you can get the most out of the rear brakes instead of some generically calibrated prop valve.


I used-

1"CPP disc master cylinder
6.25:1 pedal ratio (factory '66 manual ratio)
No booster
The usual squarebody style front disc kit
Stock rear drums
10 psi residual valve in the rear line
Wilwood adjustable proportioning valve in the rear line
Hold off/metering valve in the front line
Semi metallic pads


Semi-metallic pads are important here- organic and ceramic pads have a lower coefficient of friction and will take higher pedal effort to stop it, possibly too much effort in a manual brake truck. Look for pads that are rated "FF", the letter code its the cold and hot coefficient of friction rating, the higher up the alphabet the more friction they make. Be sure to properly bed-in the pads to get the most bite/friction out of them.

[dmjlambert]

Here is a solution discussed a couple years ago and what I went with. https://67-72chevytrucks.com/vboard/...39#post9169739

[binford]

Originally Posted by Luke87gt

Thank you, how did the corvette 1” MC feel for you?

I had planed to run disk brakes up front, so the pedal was just slighty harder to press. I sold the truck before the disk conversion and bought a 71 with disk brakes.

The 71 now has hydro brakes form a 2006 chevy van and they are awesome!!

[PbFut]

This thread has better info than most on the Master and combo valve options. I have hydroboost and find it's good for normal dry road operation. I would not like to attempt a hard threshold braking stop on a wet road or threshold braking in a performance application. The break feel is too isolated with hydroboost. I'm not going to change as there are other advantages with hydroboost that make up for the rare instance I may need to modulate in a unusual way from normal street driving. My truck is a Home Depot run, Sunday cruiser.