1" or 1-1/8" master cylinder?

[Bigdock]

Finally getting to brakes on my 64 I've got a 8" dual diapram booster and have disc brakes on front and disc brakes on the rear so which master cylinder do I need? I'm ordering from summit racing just the universal cast iron black master cylinder thanks for the help

[NEWFISHER]

1 1/8 for sure!
The more volume the better. In this case bigger is better in my experience with master cylinders.

[TJ's Chevy]

1-1/8 was stock I believe. Been awhile. But like NEWFISHER said. 1-1/8 for sure!!!! lol

[Captainfab]

You will want to be sure that the master cylinder you are getting is designed for a disc/disc brake system. I would also go with a 1-1/8" bore master.

[Bigdock]

Thanks for the help guys I checked the master cylinder and it doesn't say if it disc/disc or disc/drum just that it had 1/2-20 and 9/16-18 ports so I'm waiting on them to email me back

[Bigdock]

Called summit and talked with a tech guy and he said I needed the 1" bore for disc/disc application which is the second link but I was thinking the first link is the one I needed he said that was for disc/drum tho does that sound correct?http://m.summitracing.com/parts/sum-760101-blk
http://m.summitracing.com/parts/sum-760100-blk

[siggyfreud]

I would think 1" would be okay for disc/disc, since you're moving a lot less volume with disc brakes when compared to drum setups. But I'm also in the same situation of finding a good booster/master cylinder combo for a disc/disc.

I'm leaning towards Summit's 8" dual diaphram, and a Wilwood 1" with their adjustable prop value package.

[Bigdock]

Yea I'm also going with the summit 8" dual diaphragm in black just to blend in a little better I might look at the wilwood 1" but will I need prop valve with the disc/disc master cylinder?

Originally Posted by siggyfreud

I would think 1" would be okay for disc/disc, since you're moving a lot less volume with disc brakes when compared to drum setups. But I'm also in the same situation of finding a good booster/master cylinder combo for a disc/disc.

I'm leaning towards Summit's 8" dual diaphram, and a Wilwood 1" with their adjustable prop value package.

[siggyfreud]

You may not, but I am getting one so I can dial in my brake bias the way I like it. I think a lot depends on what rotor/pad setup you have in the back, and how the master cylinder defaults the bias.

Traditionally, rotors and pads in the back are smaller than the front, but on my setup they're the same all the way around, so I want to ensure I can dial the bias down a bit for the rear so I get the proper split with the front doing the majority of the work.

[NEWFISHER]

Since you are running disc disc vs disc drum, the master doest care what it regulates. Get the lager bore for drum drum, adjustable prop bias valve and install a 2-4lb residual valve in the rear line. This combo is what I have found to work the best and eliminate more threads on "why do my brakes feel mushy, CPP tech line is no help" or " I installed disc, now what" etc.
Spend a few hours in the brakes and suspension sections searching disc brakes and read all of the headaches and the solutions.

Ps I have never run a bias adjustable valve on a disc disc system, but have been scalded and warned. Im recommending it only as an additional safety item recommended by others.

[siggyfreud]

For Drum/Drum wouldn't you want a larger residual valve at the rear? I thought you needed like 10lbs and 2-4 was more for disc setups.

[siggyfreud]

Doing more reading it seems like the 1 1/8" is traditionally for power brakes, and the 1" is for manual, as trying to push less fluid was easier on the legs without the power assist.

[argonaut]

You aren't pushing more or less volume with either. The volume displaced is the same. The 1" bore will have a greater mechanical advantage than the 1.125". It will also have just a little more pedal travel. For a given amount of leg force, the system with a 1" master cylinder will create more force at the calipers and wheel cylinders.

[siggyfreud]

Originally Posted by argonaut

You aren't pushing more or less volume with either. The volume displaced is the same. The 1" bore will have a greater mechanical advantage than the 1.125". It will also have just a little more pedal travel. For a given amount of leg force, the system with a 1" master cylinder will create more force at the calipers and wheel cylinders.

What would give the 1 inch a greater mechanical advantage if volume pushed per amount of travel wasn't part of the equation? I thought it was that the smaller bore meant you're moving less volume per inch traveled thus it would be easier physically to push, but would require longer travel to move the same volume as larger master cylinder.

I would agree that overall you're not moving more volume in the system. But volume moved as the pedal travels would be different, yes?
Posted via Mobile Device

[NEWFISHER]

Originally Posted by siggyfreud

For Drum/Drum wouldn't you want a larger residual valve at the rear? I thought you needed like 10lbs and 2-4 was more for disc setups.

Yes, OP is using disc disc hence the smaller res valve recommended. The larger drum drum master was recomended for its bore size...bigger

[siggyfreud]

Originally Posted by NEWFISHER

Yes, OP is using disc disc hence the smaller res valve recommended. The larger drum drum master was recomended for its bore size...bigger

That's what I thought, but was just checking as your post said "Get the lager bore for drum drum, adjustable prop bias valve and install a 2-4lb residual valve in the rear line," which I now see was just a typo.

[NEWFISHER]

Originally Posted by siggyfreud

That's what I thought, but was just checking as your post said "Get the lager bore for drum drum, adjustable prop bias valve and install a 2-4lb residual valve in the rear line," which I now see was just a typo.

Not a typo.
The bigger bore cylinder is for drum drum. He is using it for disc disc and should use the smaller resi valve in the rear line.

It may sound complicated and confusing, but jf you spend some time reading builds, brakes threads etc and follow them to the end and solution, yoj will see that what I am recomending not only works for me, but others as well.

[Bigdock]

I've read thread after thread on brakes and everybody does something different but in my mind I'm pretty well set on the 8" dual diaphragm from summit and the wilwood 1-1/8 aluminum tandem master cylinder kit that includes the prop valve think I'll pass on the residual valve seems like I only need that if master cylinder is lower than calipers

[argonaut]

You want a little residual pressure on the rear if you have drums in the rear. Not necessary for disks.

[Bigdock]

I'm disc all the way around so should be good

Originally Posted by argonaut

You want a little residual pressure on the rear if you have drums in the rear. Not necessary for disks.

[argonaut]

Originally Posted by siggyfreud

What would give the 1 inch a greater mechanical advantage if volume pushed per amount of travel wasn't part of the equation? I thought it was that the smaller bore meant you're moving less volume per inch traveled thus it would be easier physically to push, but would require longer travel to move the same volume as larger master cylinder.

I would agree that overall you're not moving more volume in the system. But volume moved as the pedal travels would be different, yes?
Posted via Mobile Device

Leg force = F1=P1*A1 where P1 os the fluid pressure at the master cylinder and A1 is the cross sectional area of the master cylinder.

Caliper force = F2=P2*A2 where P2 is the fluid pressure at the caliper and A2 is the cross sectional area of the caliper piston.

P1=P2 Because it is a closed and incompressible system

Then:
F1/A1=F2/A2

If you hold F1 and A2 (leg force and caliper diameter, respectively) constant, then an increase is A1 (master cylinder diameter results in a decrease in F2 (force on caliper)

As you stated, the volume of fluid moved is a constant. So, as I said, the smaller bore master will have anlittle longer stroke.