Dual Master Cylinders: Are They All They’re Cracked up to Be?

They work. Saved my *** on several occasions...and the ***es of friends on more occasions. Rust never sleeps up here!
Unless the master cyl is shot, you can't drain out both sides just from one line leaking. They are individual systems with their own containers...or a single container with a wall down the middle to separate front from rear as the level drops.
Lose the rear and you hardly notice a difference in braking power, but losing a front will make you rely on the less effective rear drums which will slide the rear wheels anyway due to weight shift during braking.

My opinion is that the guys with a split system who had no rear brakes when a front line popped, actually had no rear brakes BEFORE the line popped due to lack of maintainance/proper shoe adjustment.

Not even gonna argue about it...
Maintain your equipment...and they WORK. Period. Been there and ALWAYS drove the car back home with no issues!

 

If you properly maintain a single reservoir system, its FINE. If you try to run a single reservoir master thats 50 years old, then yeah, your looking for problems. Its all about maintenance people. Replace the old worn out ****, and its good as new.

 

Interesting read. I found the info below the other night when surfing around and I think it provides some valid points that support continual vigilance regarding the brake systems and not to just blindly think your dual system will save you.
Ol Blue

<TABLE width="90%"><TBODY><TR><TD>by Skip Readio
skip.readio@compaq.com NSRA has recently added dual master cylinders to their list of not required but neat things to have on your street rod from a safety inspection standpoint.
While I do not dispute the fact that they are a great safety item, I do have a problem with the blanket acceptance of the device as the "end-all" to everyone's brake failure problems.
A lot of the following has to do with drum brakes as opposed to 4 wheel disc brakes.
Like most of you, I have been driving vehicles with dual master cylinders for a number of years now. I don't think I have ever owned (or leased -- I drove leased cars when I was in field service) that didn't experience some kind of brake failure. Yea, the '81 Aries was ok but I didn't have that one long enough to get into trouble. Same goes for a couple of other short-mileage examples.
However, every vehicle I've owned/driven beyond the 100,000 mile mark has experienced an hydraulic failure of some sort one or more times.
The ONLY times I totally lost my brakes were in dual master cylinder equipped vehicles.
Why is that, you ask? (I've been saying that a lot in the past few days) Let's take a look at driving habits and it'll become quite clear why reality doesn't follow theory (sound theory, but incomplete)
I am not one of those individuals who spends a lot of time performing deliberate forward/back self-sdjusting brake maneuvers. (better take a minute and explain whatb that means for out novice readers.)
Self adjusting brakes on domestic vehicles employ a cable activated ratchet mechanism to rotate a star wheel between the two brake shoes in such a manner as to maintain a minimum clearance between the shoes and drums. In order for this system to work, slack must be induced into the cable to "reset" the ratchet. You will need to understand a bit about self-energizing brakes to see how this works.
When you step on the brake pedal while the vehicle is in a forward motion the wheel cylinder expands a pair of pistons out against the two brake shoes. The front shoe snags, if you will, on the drum and the whole front shoe / adjuster wheel / rear shoe ***embly rotates slightly in the direction of the wheel rotation.
Since the brake adjuster cable is a segment of the front shoe mechanism, it goes slack and a spring on the ratchet at the bottom of the front shoe drops the ratchet down as far as possible given the confines of the system.
If, at this time, the driver comes to a complete stop and releases the service brake (takes his foot off the pedal), the brake adjuster ratchet is in the "****ed" position.
The operator then prceeds to back up and when the vehicle is rolling at 3 or 4 mph the operator performs a firm and deliberate application of the brakes. This causes the shoes and adjuster ***embly to rotate in the opposite direction. This reverse rotation of the ***embly STRETCHES the cable and actuates the adjuster ratchet.
If the shoes were far enough out of adjustment, enough motion would be induced into the ratchet to cause the star wheel to rotate one or more tooth positions thus lenghtening the distance between the bottoms of the brake shoes (and closing the gap between the shoes and the drum)
You have to go forward again and reset the ratchet if you want to get another rotatation of the star wheel. You can't keep backing up and hitting the brakes. They only adjust themselves on the first application after a deliberate forward-motion stop.
If the brakes are propely adjusted there won't be enough movement in the cable to cause the ratchet to increment the star wheel so once they're adjusted, repeated forward/reverse won't over-adjust the system.
Ok, now back to the problem. I, and a lot of other people don't, in their normal driving mode, sufficiently adjust their drum brakes.
If the vehicle is 4 wheel drum, the brake pedal, over time, gradually sinks to the floor. Something clicks in the brain and the brakes are either serviced or the neighbors look at you in wonderment as go forward and back in your driveway.
With a disc/drum combo, the failure to adjust the rear brakes isn't anywhere near as apparent. We have to look at the basic master cylinder design to figure that one out.
First off, the dual master cylinder is a pair of pistons not mechanically connected to each other (unless there's a failure and we'll get to that later)
The piston closest to the brake pedal has a pair of packings, both facing forward, that cause brake fluid to flow when the pedal is depressed.
When you step on the pedal fluid is forced by the rearmost packing out into the brake lines to actuate the front brakes (they do 60% or so of your braking, depending on vehicle weight displacement).
The frontmost packing forces brake fluid against an opposing packing that's on the rear of the front piston. i.e hydraulic pressure within the master cylinder is employed to actuate the piston controlling the rear wheel cylinders. the front packing on this piston sends fluid out to the rear wheels.
If there's a loss of pressure in the rear cylinder (the one controlling the front brakes) the rear piston comes into physical contact with the front piston 9the one controlling the rear brakes) and the pedal is now mechanically connected to the rear brakes.
The problem with this scenario is that there isn't enough pedal travel before you hit the carpet to get adequate application of out-of-adjustment rear brakes.
With disc brakes, no appredciable amount of fluid flows back into the master cylinder after application of the brakes so they're "self-adjusting" and any hydraulic pressure increase has an immediate effect on the application of the brakes.
With drum brakes, you have to re-fill the wheel cylinder each time because the return springs on the shoes force the brake fluid back into the reservoir.
That's why disc brake reservoirs are larger than drum brake reservoirs. The drum fluid is "recycled" while the dusc fluid isn't.
So, HERE'S WHERE THE FALSE REASURANCE PROBLEM ARISES. In most systems, the front brakes will more than adequately stop a vehicle in normal driving conditions. The pedal resistance will be pretty re***uring and even if there's a hole in thne rear brake line, it won't be readily apparent because the pedal "feel" tells you everything's OK. Not perfect, but OK. What WILL happen if there's a hole in the line is the brake warning light will come on.
But let's say there isn't a hole in the line but the shoes are just way out of adjustment. The spring pressure (brake return springs) is going to present enough resistance against the switch in the combination valve so that, UNDER NORMAL BRAKING, the light won't come on telling you there's an imbalance in the braking systems. This can go on for months and although you're still actuating the rear brakes (and wearing them down) you're never ever lighting that lamp on the dash that says you got a problem UNLESS you panic stop and really bear dow on the pedal. THAT'LL get your attention.
Anyhow, I've lost the front brakes in my '72 Dart and, because the rears were well enough along, I lost everything. THAT was a fun ride home ...dropping the trans into low when I anticipated stopping, left hand constantly on the parking brake lever (yea, it's a pull it out then rotate to release type)
Just before I left for Australia this past February I blew a brake hose on a front caliper on my wagon. Again, rears were on the loose side and Bingo, no brakes. Luckily the car's a 4 speed and it was fairly late at night. Got that one home, too. Fixed it when I got back 5 weeks later.
My old Volare wagon lost caliper hoses twice with the same results and my GTX did it to me once way back in 1971.
Now, I currently own two vehicles with single master cylinders. One's my hemi-powered '34 and the other is the '48 Chrysler 7 p***enger sedan. Both of those cars have lost wheel cylinders and master cylinders but on EVERY occasion there was prior warning that things were about to fail.
Spongy pedal, rebuild the master cylinder. Low pedal, top off the master cylinder and rebuild the leaky wheel cylinder. Drop of brake fluid on my toe, top off the master cylinder then rebuild it when I got home.
Normally, low brake pedal, adjust the brakes.
I'll probably convert the '34 to a dual master cylinder but not because it's the politically-correct thing to do, because it isn't. I can't get rebuild kits for that old Ansen swinging pedal ***embly any more.
Skip Readio
skip.readio@compaq.com
Early hemi s.m.e.
Street rod wiring consultant
Freelance rod & custom journalist
</TD></TR></TBODY></TABLE>

 

That's nice and all - but I lost a seal in a wheel cylinder on my ranchero and had NO brakes. Had fun coasting through a red stoplight in los osos. Single MC. (changed right after)

Sure, if your rear brakes don't work for **** - then a dual MC isnt going to do you any good... that's just a trueism. A properly functioning dual MC w/ properly functioning brakes is a world beyond a single MC setup for safety.

It's not that hard to make sure your rear brakes are adjusted properly...

 

This is one of those rare times where I would tell someone to their face that they're an idiot.
I don't even know where to start with something this stupid. Let's just pose a quick question about when these things were federally mandated in '64...does anybody really think that the Big Three, who weilded a whole lot of power back then, would have just rolled over for the Feds without a fight if they didn't think it worked?

I had new lines on my car, NEW damn wheel cylinders, and I rebuilt the master cylinder. And the rear wheel cylinder let loose.

But you're right...that was probably a one-in-a-million fluke. Who's ever heard of brand new parts from the auto parts store failing?! ****, that wouldn't happen.

They're called "accidents" because they are unexpected. If you expected them, they'd be called "plans." Nobody plans on their wheel cylinder blowing out, or a rubber line rupturing, or any of the other problems that occur. Just because you've never personally experienced it, doesn't mean a nice, new wheel cylinder can't blow. I've had it happen, and I garaun****ingtee other guys here have too.

The solution, therefore, is to make you're brake system redundant, so that if they DO blow out do to an unexpected problem, you don't end up going through a stop sign and getting T-boned.

Jeez...what the **** is so hard to understand about something this simple? If you have ONE bucket feeding four hoses, and one hose gets cut, the other four hoses will not have pressure in them. If you have two buckets, each feeding two lines, and one of the four hoses gets cut, you still have pressure in two of the hoses. The brakes are the single, absolute most important thing on your vehicle. Why would anybody fight about something like this?

I know that when the fronts went out on my Dakota, it took a lot of pedal travel for the rear drums to stop me, and it wasn't quick...but they did stop me. And I do know that when the NEW wheel cylinder popped on my Buick, I did NOT stop until I was in the far lane of a 4-lane highway.

But don't believe me or anybody else who has a similar story...we probably were slack in our vehicle upkeep.
-Brad

 

What the other guy said. This is just dumber than hell.

 

When automotive engineers came up with a dual master, there was a reason. Now when you think running a single master is better and you a smarter than people with mechanical engineering backgrounds and years of automotive research and testing..... let me know your theory of absolutely considering a single master over a dual master system.

 

" beats the **** outa plowin into stuff at any speed"[/quote]#11
It beats walkin too!
"Its my understanding that without the use of a 'combination' or 'safety' valve, you are not getting the safety factor that you think you are."[/qoute]#16
proportioning valves more ***ociated with dual systems as are idiot lights.
"Nobody said a Hot Rod wouldn't kill ya"G.T.

 

<meta http-equiv="CONTENT-TYPE" content="text/html; ch****t=utf-8"><***le></***le><meta name="GENERATOR" content="OpenOffice.org 2.0 (Linux)"><meta name="AUTHOR" content="David"><meta name="CREATED" content="20080303;23191200"><meta name="CHANGED" content="16010101;0"> <style type="text/css"> <!-- @page { size: 8.5in 11in; margin: 0.79in } P { margin-bottom: 0.08in } --> </style> Proper design, proper installation, proper maintenance. These are required to make the brakes work every time. Miss one and you might have them work most of the time.

Open a bleeder on your "dual" system and stomp the brakes. Your foot go all the way to the floor? If it did, your dual system isn't working correctly, that is, its not working how a dual redundant system is supposed to work. Its either broken, installed wrong or designed wrong. Designed wrong would be leaving out the slider valve REQUIRED for proper redundant dual systems. Fix it.

Open a bleeder on your single system and your foot IS going to the floor.

Which system is safer? I suppose that is dependent only on the operator. If you smart and diligent, both are safe. If you are lazy and stupid, neither are safe. David

 

My son showed up from college in his (OT) honda accord with one rear wheel soaking wet with brake fluid. His front brakes were not affected and he didn't even know he had no rear brakes at all.

Front brakes are a whole lot better than no brakes. Rear brakes are a whole lot better than no brakes

 

It's okay,Brad. They probably won't be posting here very long. Just hope others don't go with them.

 

I was thinking about this and does nobody really run an E-brake? if you do wouldnt this put a 3rd to the saftey of your rod??

 

I had a properly e-brake on the '54. A (new) rear wheel cylinder blew and coated the inside of the drum with brake fluid. No fronts, one slick/useless rear, one good rear that tried like a hero with the cable-actuated E-brake, but didn't do too much more than absorb my effot.

-Brad

 

OK, enough already! Car nuts spend piles of cash on powertrain mods and good looking cosmetic stuff and some will step up to the plate and build an excellent tandem brake system. Sadly, some don't bother.
1. Regular brake maintenance and inspection is mandatory!
2. 4-wheel discs far superior to disc/drum combos.
3. Rear drum adjusters will over time will sieze and fail to maintain minimum shoe-to-drum clearance. Hence the pedal going to the floor upon front system failure.
4. Rear braking effectiveness on small front wheel drive cars is only 5&#37; max. according to Raybestos information. (and that is if they are regularly serviced)
5. Brake fluid should be changed every two years to remove condensation contamination.
6. Examine every new component you install on your brake system. I have encountered a few incorrectly ***embled components. (you do need to know the difference between correct versus incorrect ***embly)
7. Make sure the front sliding calipers slide. Rust ac***ulates causing caliper siezure, causing uneven disc wear, causing hard pulling to the left or right during braking. Both sides rarely sieze at the same time. An anti-sieze compound applied to the sliding surfaces reduces rust buildup and lubricates as well.

What is really scary is the knowledge that way too many vehicles that we share our highways with have inadequate brake systems, having had little or no maintenance service since leaving the ***embly line. I won't tell you what I've seen come into the shop - you may not want to take your prede-and-joy out for a cruise. At stop lights, stay a car length behind the car in front - this gives you somewhere to go if the idiot behind you "needs a little more stopping room". It has helped me out of a couple potential rearenders.

 

I'm running a rebuilt single master on my '52 Dodge with all new brake parts and lines all around. It's a calculated risk but I check my brakes/lines/e-brake (drum brake on the driveshaft!) religiously every time I cruise. I honestly don't drive the car often enough or fast enough or far enough to upgrade the brakes right now within my budget. Heck, if I installed a dual m/c the car still wouldn't stop worth a damn without discs
If you drive smart and anticipate brake failure at every stop, you'll probably be ok. Swapping to a dual m/c is a little more work and money than some let on (at least on my car): m/c $25, fab bracket (and avoid problems with shift linkage, clutch linkage etc), mod brake lines, upgrade to front discs $$$, new disc brake wheels, new tires, etc. it adds up! Just my .02

 

Both of my personal experiences were with cars having a fully functional E-brakes - prior to the event. In one case it was rendered useless because it was hooked to the tailshaft of the trans ('57 mopar torqueflite trans) - broken driveshaft = no "E" brake.

On the other incident - **** happened so fast there wasn't time to grab for the E brake. What saved my hiney was that the front system still worked.

Next thing to consider is how effective is your ebrake?? Say you DO have time to pull it - how well do you think it'll work at slowing you down in a panic situation going 70 mph - like I was??? Go out on a deserted road and give your Ebrake a test pull - you might find yourself surprised at how effective (or rather how ineffective) it really is. Don't get me wrong - it sure as hell is better than nothing, but you aren't exactly pulling negative G's with it either.

BTW - In BOTH these cases the brake systems were FACTORY designed setups in the origional vehicles - and FYI YES the pedal DOES drop to the floor - it doesn't BOTTOM OUT on the floor but it DOES and is supposed to drop - nature of the design. ALSO for the record - just because you have a proportioning valve DOES NOT mean you automatically have a 'slider valve' separating your system - cut some apart and peek inside - they're not all the same.


the arguement abou tmaintaining your system falls on deaf ears - it's not that I don't agree 'cause I do - it's just that you CANNOT always control or have prior warning to impending failure. Who would have guessed my broken driveshaft would cut the rear brake line - surely not me. But in the spirit of living and learning - I tried to improve things afterwards - bigger OD driveshaft - twin safety loops - just to name a few mods.

Guys put yourself in the position of justifying your actions after the fact to the parents of the kid you just ran over - tell them how much cooler your car was for having that fruit jar M/C on it - I'm sure both YOU and THEY will feel much better. NOT!!!!

In all the years this topic has come up I have NEVER ever read a convincing arguement for running a single m/c. This thread is no different. I especially love the arguement that goes like this, "I have been running a single M/C for 50 years and it's never let me down!"
Yeah and my Father-in-law has smoked cigarettes for 50 years - that must make him living proof that they are 100% safe too....

 

after losing all brakes on a single reservoir system am switching over to a dual system with correct valve..something is better than nothing...

 

Hard to believe there's even a debate between the merits of single vs dual M/C's..............

 

you cant debate that single is better than dual, although i do have a new stock single master in my shoebox along with new lines, hoses, and wheel cylinders, i haven't had any problems yet, although i do realize new parts can fail, they just haven't failed on me yet...i also believe that having an standard transmission and a correctly working emergency brake lessens the dangers of running a single reservoir brake system. and also...dont drive like an idiot!

 

When it comes to brakes, steering and suspension it's really simple:

How cool is dead - either you or the guys you take out?

How would you enjoy life as a quadriplegic as a result of the few $$$ you saved by not bringing your brakes up to modern standards?

How would you enjoy seeing your car totaled, and spending months in hospital recovering from your injuries?

How would you enjoy being sued by the innocent victims of your stupidity and stripped of everything you own or would ever hope to own?

How would you enjoy seeing your hot rodding career terminated immediately and permanently? All this because you were too cheap and too stupid to use the technology available to you.

The reason modern cars have better brakes than older cars is called progress. If they had had better brakes back in the day they would have used them.

The reason that government mandates safety standards is, more often than not, for people who are too stupid and irresponsible to follow safe practices for themselves. Dual master cylinders should be mandatory for all re-engineered road driven vehicles.

Ultimately, how many dollars is your life worth? Go figure.

Safety is no accident.

 

the one quality I haven't seen expressed here is the most interesting one, I think...

in the event you lose a line on a single resivoir system, the pedal goes to the floor and STAYS there.( unless you have a return spring on the pedal) there is no pumping the brakes, they're just gone.

with a dual cell, you can at least go through the motions of pumping to slow it down.

 

Single reservoir systems are acceptable IF you have a functioning emergency (Cable operated) brake-

 

Running a single MC is like jumping with one parachute...

 

I have had a single system fail, when the rear hose unscrewed from the T. I have had dual masters go bad, and still got home safe. Guess what is under MY car now?

 

ware live you have 2 have a duel no questions asked