Master Cylinders/ lets talk about this logically

There are countless threads on here talking about master cylinders and everybody has a different opinion on it. Lets take a common example of the corvette disk/disk 1" bore master. Why would the master care if it was disk disk or disk drum? If it is a one inch bore that does not change no matter what it was intended for. The difference I would understand is that the disk use more fluid as the pads wear so it would have a larger chamber, but functionality should be the same. Also, why would a master cylinder care if a power brake booster was in front of it from the factory as well? I am just trying to make sense of all the info out there on this in a logical manner. Pleas help me understand all of this.

 

One issue is some master cylinders have residual pressure valves built in for drum brakes, use them with discs and the calipers will drag. Another is fluid capacity, disc calipers displace more fluid than wheel cylinders. Often GM used different pushrod lengths to keep someone from accidentally using a drum master with disc brakes and vice versa.

 

if your mastercylander has a divider for front and back dose it mater which one you make the front or the back? my mastercylander is under the floor so the front of it is closer to the back of the car.

 

Usually the larger cylinder goes to the front brakes. Always worked for me

 

Larger chamber for front disc brakes as they use up fluid as the pads wear down.

Drum brake cars had the residual pressure valve to hold the cups tight to the wheel cylinders and prevent seepage. In 1975 or 76 they came out with a new design of wheel cylinder with spring loaded cups, after that they did away with the pressure valve. At least this is true of Chrysler products, does anyone know if other car companies followed suit?

 

You're right, I have used drum M/C's and vice versa on drum/drum, disc/drum, and disc/disc systems. The M/C doesn't care where the pressure is going. Now as far a residual valves, bore size and pedal ratio goes, you do have to have things in order, and sometimes you have to swap bore sizes or change the pedal ratio to make a system work.

With the smaller chamber drum M/C's on a disc car, you do need to keep an eye out for the fluid level. Also, alot of power brake M/C's will not have the groove in the piston that will accept the push rod lock, so the push rod could fall out!!

 

Why not just get a vacuum can?

 

Harder. You are now pushing all that air against the diaphram that the engine vacuum would be moving for you.

 

They are basically the same, except most power masters have a deeper push rod bore, needed when using a non-retained custom or non-stock push rod.
Some manuals will also have a dust boot retainer ring.

 

With the vacuum depleted, the pedal wil have a mechanical connection (by law) through the booster to the master, so you will in effect have stock manual brakes with the 6:1 ratio. The only thing that may be different would be a larger master bore size that came from the factory on some power braked vs non-powered vehicles that would result in higher pedal efforts.

 

One of my vehicles (not HAMB friendly) has discs up front and drums in the rear. In addition to the residual valve, there is also a proportioning valve. So, presumably you need different pressures for disc and drums.

 

What hasn't been mentioned is the area of the master cylinder compared to the area of the caliper/wheel cylinder. Changing the ratio between those two has the same effect as changing the pedal ratio. The bigger the master cylinder bore the more fluid it moves. The smaller the master cylinder bore the harder it pushes on the caliper/wheel cylinder for a given amount of pedal effort. And, bigger bore means less pedal travel than smaller bore.

 

In order to get a logical grasp and a intelligent conversation on master cylinders , you'll need a basic understanding of general physics, fluid physics, ratios, and some basic math. Those will get into a hypothetical discussion.

You'll need to know bore sizes, travel distance and fluid displacement to get into the particulars of a system.
Knowing the above you'll be able to build any brake system from any thing you want via junkyard wizardries.

Without that , you'll be reduced to buying kits or swapping the entire braking system from a donor.
An example would be Every component from a S10 pickup onto a similar weight hot rod would stop just like the S10 pickup.

 

Jeff K. you should consider an alternator off a small jap diesel truck these things still charge your battery but also have a vacuumed pump on the rear of the alternator. That way you will have a nice pedal and a big camshaft. The other thing to consider is a hydro boost these are in Chevy C 20-30 from the late 70's these run hydraulic power steering pump to an oil powered booster. But I don't think you would have the room in your corvette for one of these. Good luck with what ever you decide

 

Very good question, and my experience is it doesn't matter. I've used drum/drum masters and put them on disc/drum setups by adding an adjustable prop valve.
I've also used manual masters with and without the power booster, on the same brakes and car.
I recently purchased a 4 wheel disc master/booster for my project, and removed the booster, and ran it manually on my disc/drum setup, and it's worked great. It also had 4 output ports and I blocked off one each front and rear to run one line to the front through my line loc, and one to the rear through a adj. prop valve.
So I guess I'm with you and don't understand all this either.

 

Thanks for the input guys. Seems what I was thinking is correct. I believe people have tried to make this more complicated than necessary over the years. Regardless, some good infor here that I hope helps others in the future.

 

No...I don't think people are making things more complicated than need be.
In fact...YOU are!

Heres why:
When you're talking cars, for every rule theres an exception.
Master cylinders are a good example.
Mix and match and you may find that some drum masters don't have RPV's and will work fine on a disc setup.
Same with proportioning valves...all kinds of stuff.

The PROBLEM with that thought is simple.
You have to experiment and if you're lucky you have a 50/50 shot.
IF...you're lucky.

The basic reason for many of the rules "experts" offer to less experienced builders is that by following those rules you have a much better chance of getting a working system instead of a useless or compromised system.
You save money, you save time and you might even save the car or a life.

Things can still go wrong of course. Even following the rules is no guarantee that something else won't pop up and bite you!

Personally I don't see the sense for going against the grain on something like a brake system. Too much to lose.
All this stuff has been thought out thru the builds of countless Hot Rods over the years and the basic rules have resulted from all that for a simple reason:

Following them you have a much higher percentage of successful builds...

Nobody says you can't experiment if you want but don't pass off accepted and sensible build guidelines as old wives tales just because you got lucky.

 

Don't get me wrong, I with you. I researched all this until I turned blue but in the end I realized some of the guidelines did not make sense. Like the power brake master would be the same internally, but I did learn from this thread that they may not have a locking push rod or enough length for it. All good info so we can choose one more logically and know what to look for.

 

kind of harsh. simmer down a bit.

 

There is no logic in hotrodding - We all know that by now.LOL

 

Seriously?

Where do you see me simmering? I'm just stating fact.

He was suggesting that because he's a little confused with a huge amount of research done in a very short period of time, that none of the info he found is reliable...and then posting that finding as though its fact.

I'm sorry...that attitude needs to be nipped in the bud as it has the potential to make less experienced builders ignore things and just start bolting things together...with NO research at all.
That just won't cut it because the ultimate result can be a hell of a lot harsher than anything I said.

 

Its easy to spot , just look for a thread like " help brakes don't work " or something similar. There'd be hundreds of them. I bet we see another one soon.

 

The rear or firewall nearest port is for the rear brakes.The actuator rod pushes this inner piston first, thus slightly applying rear brakes before fronts.You can watch this thru clean fluid when bench bleeding. On your aplication the port closest to the rear of the car would actually go to front brakes.

 

I did not post anything as fact. Simply trying to get more input. The only attitude needing to be nipped is your condescending tone. Please take it to another thread.

 

I'm not trying to be condescending...and if you think that, I apologize.

In the last quote you said you didn't post anything as fact...
but in the first quote you said that you believe people have made this more complicated than necessary...and in the second you said that you researched till you were blue in the face but things didn't make sense.
Those are pretty solid statements to make.

All I'm saying is that there is a huge amount of info available because the subject is a complicated one and a simple, straightforward answer might not be obvious for each individual combination.
That doesn't mean that the available info should be dismissed.

This blanket statement worried me.
"Seems what I was thinking is correct. I believe people have tried to make this more complicated than necessary over the years."

Thats just not a good thing to say around inexperienced people who are building their first car!
It could give some of those people an excuse to just bang something together without any thought or research at all and someone could easily get hurt.

Thats ALL I'm saying!

If you're reading more into it than that, then you're reading way too hard because I'm certainly not trying to pick on you personally.

 

Go HAMB, now so what I'm hearing is that I don't need proportioning valves when running drum/drum combo with manual master on a hot rod?

 

That simply is NOT true! Many masters have the primary port/chamber going to the fronts, while others have it going to the rears, even within the same car line. It depends on vehicle application, period. What IS true is the larger chamber ALWAYS goes to the fronts, and is obvious on disc/drum and some drum/drum masters.

 

Production drum/drum vehicles never used proportioning valves, only disc/disc and disc/drum systems. However, when mixing ineffecient non-servo brakes on the front, like old Ford Lockheeds, with modern dual servos on the rear, an adjustable prop valve isn't a bad idea.

 

Could you give an example of your statement? I am led to believe the larger reservoir goes to the rear brakes.
Thank you

 

I have to ask who led you to believe that? Go look at ANY car/lt. truck master cylinder with obvious chamber size differences and follow the lines to the brakes. Generally, most masters bias the fronts in volume, even if the chambers look the same. Exceptions would be some drum/drum and disc/disc vehicles, where the master is split 50/50, and front plumbing could go to either port.