Brake master cylinder: vacuum vs. hydroboost?

[IDIoit]

I will let you do the math...but I will explain principle

2 mc

1.25

1.3125

Pi R Sq = Surface area

Surface area x 1000 lbs force from booster....1000 is an example number = psi

Thus the larger MC vs the smaller MC =

Larger has less psi however greater volume to fill wheel cylinders and calipers
Smaller has higher psi however lesser volume to fill wheel cylinders and calipers

It is very basic and easy to prove....

Just sayin

Personally I run the Hydroboost MC

JM7.3CW

thank you for your explicit proficient analogy of why i should run the hydro MC.
please forgive my ignorance for not knowing which would work with which, also handing information on a half polished silver platter.
i had not a clue if there was a difference inbetween the two.
due to my lack of knowledge and obviously what should be common sense,
i shall now repent and move forward in life.
lets all bow to thee Al Mighty Riot warrior

 

[riotwarrior]

thank you for your explicit proficient analogy of why i should run the hydro MC.
please forgive my ignorance for not knowing which would work with which, also handing information on a half polished silver platter.
i had not a clue if there was a difference inbetween the two.
due to my lack of knowledge and obviously what should be common sense,
i shall now repent and move forward in life.
lets all bow to thee Al Mighty Riot warrior

 

[IDIoit]

it's correct.if you zoom in you can see the bore size on the unit in the pic.it's the one i bought for chip truck so i know first hand it's the one too.

the extra port you must be thinking of im guessing is on the power steering pump reservoir.

You must be registered for see images

the part number for that is: E5LY-3A697
but the last i remember they are no longer being made.you'll have to score a used one,T the return line,or make your own return tube in yours.
i bought mine here:
http://www.fordpartsgiant.com/parts/ford-reservoir-asy_e5ly-3a697-a.html

though since members claim they are discontinued.id call before placing my order to see if they actually have it.

not doubting ya man, just tryin to dot I's and cross T's
looks as if the master cylinder has an extra threaded hole in it, could be me.
i already have a extra return in my PSR,
that i bought after i also heard they were discontinued. bought mine with a remaned PS pump, for 60 ish bucks.

 

[cpdenton]

Make sure to orde a master cylinder for a 92 or older f-superduty. The extra threads hole on the units newer than that I s for the cruise control cutout switch(you know, the one that was burning down trucks).

The master cylinder for your year model truck is identical other than the threaded port for that switch.

I bought one from rock auto on a close out deal for 13 dollars. It is on the shelf for future use

 

[icanfixall]

thank you for your explicit proficient analogy of why i should run the hydro MC.
please forgive my ignorance for not knowing which would work with which, also handing information on a half polished silver platter.
i had not a clue if there was a difference inbetween the two.
due to my lack of knowledge and obviously what should be common sense,
i shall now repent and move forward in life.
lets all bow to thee Al Mighty Riot warrior

Al not all this is exactly correct. True.. A larger master cylinder bore is pushing more fluid per stroke but remember that the hydroboost peddle pin has been moved up around 1 inch. So this changes the travel and the possible pressure exerted on the master cylinder. The hydroboost brake booster increases the "possible" pressure in the system by nearly double what the vacuum booster can do. So in the end results we have nearly double the braking power when we modify to the hydroboost brake system.

 

[LCAM-01XA]

Al not all this is exactly correct. True.. A larger master cylinder bore is pushing more fluid per stroke but remember that the hydroboost peddle pin has been moved up around 1 inch. So this changes the travel and the possible pressure exerted on the master cylinder.

^^^ This. Boosters aside, the larger bore and thus somewhat lower internal pressure of the big master is compensated for by the shorter travel of its piston and increased input force suppiled by the pedal. IMHO there's two ways to do the hydro swap and make it all work good:

1) the full swap with pedal and booster and master

2) keeping the factory master and pedal, and relocatin the mounting studs for the hydroboost unit so its pushrod sits on the firewall at the exact same height as the vacuum booster.

Been done it both ways, IMHO there's little to no noticeable difference in performance between them. You start mixing masters and pedal ratios and things can get goofy real quick, keep the master matched to the pedal and all will be well. Ultimately the booster itself is just a force multiplication device, it cares not what's on either side of it, the only difference between the hydro and vacuum is the multiplication factor...

 

[hce]

I left the stock cast iron 1-1/8" master cylinder and pedal, when I swapped for hydro boost. Master cylinder slide right onto the hydroboost. If I upgraded the master cylinder I would have needed to change fittings on the brake lines or find adapters. On the 84 the brake pedal pushrod was in the same position on both the vacuum booster and the hydro boost. As expected very little effort to apply brakes, but the odd thing is the pedal travels is much less, even after adding larger 1-1/8" rear brake cylinders. Guessing that the pushrod out of the hydroboost was a bit longer so there is less dead pedal travel. Never had problems with the self adjusters not working before or after. Very happy with all aspects of the upgrade, brakes are very well behaved from hard stopping on dry pavement to ice covered roads.

 

[riotwarrior]

Al not all this is exactly correct. True.. A larger master cylinder bore is pushing more fluid per stroke but remember that the hydroboost peddle pin has been moved up around 1 inch. So this changes the travel and the possible pressure exerted on the master cylinder. The hydroboost brake booster increases the "possible" pressure in the system by nearly double what the vacuum booster can do. So in the end results we have nearly double the braking power when we modify to the hydroboost brake system.

^^^ This. Boosters aside, the larger bore and thus somewhat lower internal pressure of the big master is compensated for by the shorter travel of its piston and increased input force suppiled by the pedal. IMHO there's two ways to do the hydro swap and make it all work good:

1) the full swap with pedal and booster and master

2) keeping the factory master and pedal, and relocatin the mounting studs for the hydroboost unit so its pushrod sits on the firewall at the exact same height as the vacuum booster.

Been done it both ways, IMHO there's little to no noticeable difference in performance between them. You start mixing masters and pedal ratios and things can get goofy real quick, keep the master matched to the pedal and all will be well. Ultimately the booster itself is just a force multiplication device, it cares not what's on either side of it, the only difference between the hydro and vacuum is the multiplication factor...

The question was regarding mc not boosters.....hence my use of 1000 lbs of force for an example.

What I presented is true and can be proven via math and this thing called physics, repeatadly.

Now change the force by what ever means you choose...and if same forc is applied to both MC the same holds true.

The question was about the MC

NOT BOOSTERS & PEDALS

I am in no way saying the hydrobokst setup doesnt make MORE pressure; just that all things equal the big mc overall makes les psi a d more volume.

Make sure you are comparing apples to apples guys....

For example...new pedal w higher pin for hydro booster...attach small mc get more psi than large mc...again...pedal pin and booster remaining same...for both mc...physics and math dont lie


JM7.3CW

 

[Black dawg]

Please for the rest of the worlds sake, DONT MODIFY MASTER CYL EARS TO FIT A BOOSTER!

There are always other masters that will fit.

 

[LCAM-01XA]

The question was regarding mc not boosters.....hence my use of 1000 lbs of force for an example.

What I presented is true and can be proven via math and this thing called physics, repeatadly.

Now change the force by what ever means you choose...and if same forc is applied to both MC the same holds true.

The question was about the MC

NOT BOOSTERS & PEDALS

I'm not saying you're wrong, cause you're not. But you DO have to look at it as a system as well - unless the hydro is modified it calls for a pedal with a changed ratio, and regardless the hydro's boosting abilities the new pedal ratio alone will require a larger master. So while the larger master alone does have the effects you described, they are offset by the changes in pedal ratio necessitated by the booster's mounting setup. Now if the boosters would freely interchange and there was zero need for swapping pedals with different ratios, then yes, the masters can be looked at individually and not necessarily as part of a matched system.

 

[riotwarrior]

I'm not saying you're wrong, cause you're not. But you DO have to look at it as a system as well - unless the hydro is modified it calls for a pedal with a changed ratio, and regardless the hydro's boosting abilities the new pedal ratio alone will require a larger master. So while the larger master alone does have the effects you described, they are offset by the changes in pedal ratio necessitated by the booster's mounting setup. Now if the boosters would freely interchange and there was zero need for swapping pedals with different ratios, then yes, the masters can be looked at individually and not necessarily as part of a matched system.

But e question is in regards to slotting the stock vacuum booster MC to fit hydro or use stock hydro MC

So all is equal...but not equal...now isnt it

 

[LCAM-01XA]

But e question is in regards to slotting the stock vacuum booster MC to fit hydro or use stock hydro MC

So all is equal...but not equal...now isnt it

But there was also the idea thrown out there to relocate the booster so that no pedal change would be needed. In which case one should either slot a '87-up master or use a '86-down as a direct bolt-in unit, and while using the ginormous F-superduty master is still definitely possible it is IMHO a pretty foolish thing to do (for the same reasons you described).

 

[FORDF250HDXLT]

it's always good to know all the possible ways to do something,then we can all make a more informed decision.
we're all in agreement here basically,simply using different words to say it.
either do the complete f450 swap with booster,master and pedal or to keep the same geometry,simply use the f450 booster with the pickups master and stock pedal by sliding the whole works downwards by drilling new mounting holes.not a bad option either,cus you've no need to worry about scoring a f450 pedal nor buy a new master.im really some happy with the complete f450 goods.one things for sure,get the geometry wrong and it's nowhere near the setup it should be.i know this first hand.ugg.
do it one way or the other but do either way correct and it all kicks vacuums ass.

 

[IDIoit]

i have purchased the correct master.

keeping the stock hole placement of the steering column bracket/firewall
will be looking at either using the brake pedal with my clutch/brake set up, or re-drilling my brake pedal for the correct height of the pin/HB arm.