The Stovebolt Site Forums The Shop Area General Truck Talk brakes

I was wondering how safe is to keep the original type of master cylinder in my truck everybody is telling to put a dual master in it?

Nothing wrong with the original type master cylinder if it is in working order. The reason that the dual circuit is considered safer is that it splits the system into separate front and rear circuits. With the system split, if a leak in the system occures, like say a blown line or wheel cylinder, you still have the other circuit to provide braking power.
Converting over will depend on what you plan to do with the truck. If you are going to do a disk conversion, a dual system is pretty much manditory. You would also want to consider it if you plan to use the truck for highway/long distance driving. for short distance, car show, occasional weekend cruise type use, the original MC will be just fine.
I will admit, I am still using the original style on mine, and have had no problems with t, either in town or on the highway.

It is fine,rebuilding mine now. Just watch your old brakes lines as they may have deteriorated.

Hank

I'm still trying to figure out what the huge advantage is when it comes to a duel system. I know it sounds good and of course looks good on paper, but have you experienced the function, or I should say lack of brake function when 1/2 of the system fails.
I had this experience when a rear brake line burst leaving the front disc system to stop with.

The only thing I can say is it sure falls short of giving the kind of brake action I thought it would provide,especially since it left the best braking half of the system...the frt. disc.
I'm not saying it's worthless, I just expected more and I don't expect to save my life if it happens again.
The only thing I'm betting on is a good brake system be it single or duel.
Dan

The single master is perfectly adequate and was used by most all cars and trucks well into the muscle-car era. Our trucks have what was then called an "emergency brake" a cable operated back-up system (now called a parking brake) and from what I've read here and elsewhere works a whole lot better than 1/2 of a dual system in an emergency. I've been driving single systems for longer than I want to admit and never had a failure. Keep them adjusted and periodically inspect everything, you'll be good to go IMHO.

I've had failures on both types of systems, and I'm here to say I'd MUCH rather have half a brake system, or less, over having none at all! The biggest problem most people have is the very low pedal that happens when one part of the hydraulic system fails. It's necessary to push past the spongy feel and get to the part of the pedal stroke where there's some stopping power left, and most people panic when the pedal gets low.

I lost the brakes on a 59 Burb at interstate speed, with a 16 foot heavy trailer hooked up. If I hadn't had electric trailer brakes, it would have gotten nasty, as traffic was stopping in front of me, and I had nowhere to go but onto the shoulder. An incorrectly-secured brake line had rubbed through from vibration, and the single-chamber MC dumped all the fluid in about 4 pedal strokes. I've had two relatively modern vehicles develop pinholes in rusty brake lines in the past 6 months, and both times, I was able to drive to my shop in relative safety to repair things. If a dual system is available, I'm going to have it!
Jerry

Jerry, I hear what your saying and would rather have a duel system,but I don't understand why all the pedal travel when the systems are separate in the master cyl. and the working system is the front disc. which has better stopping power than the rear drum.
With the pedal near the floor and standing on it, waiting for the car to stop.
Maybe there's something I'm missing about the hyd system.

Dan

Basically you have two pistons in line in the master cylinder. When on system fails, the pedal has to take up the stroke of the failed system before pressure develops in the other circuit. I would imagine that a second quick application of the pedal would help things out a lot. I could see where mere panic might prevent the second stroke with some drivers.

I can't see what your saying. There's one piston in the master operating two separate systems. The only thing I can't figure is the proportioning valve which is there to prevent the front disc from applying until the rears have had time to apply.
Now how the P valve works when the rear fails is the part I have no knowledge of.
Dan

I only have dual master cylinder vehicles and have never experienced a brake line failure - for educational purposes, if a brake line does fail on a dual circuit system, do you need to pump the brakes to get the pedal to rise for an effective half system brake stroke?

The dual master does offer some protection against a line or wheel cylinder or caliper failure. Today these are very unusual events but when our single master trucks were new it was common enough that the concern turned dual masters into a legal requirement.

My own feeling is that if you have replaced every line and cylinder in your original single master system, and are going to honor the original service cycles you are probably fine with a single master.

Otherwise the dual master is cheap insurance against no pedal and no brakes.

glasman,
if you look at how a dual master is designed, there is a piston between the front circuit and the rear circuit. That piston is forced into action by the pressure in the rear most circuit in the master. At the rear of the master there is another piston which is has mechanical linkage to the brake pedal.

When the rear circuit fails, the rear piston bottoms on the second piston and then you have pressure in the front system. If the front system fails, the front piston bottoms toward the front and then you have pressure in the rear system.

This explanation is given in Petersen's "Basic Chassis, Susupension & Brakes".

Thanks for the refresher on master cyl. I guess if I had opened a book I might have seen that.
It's been awhile since I've torn one down, mostly cause when one was needed we just traded the old for a new or rebuilt.
WOW, it's 2010, time is flying, that was over 20 years ago when I tore one down.
I think I might be getting old. Ya know, in my mind I still think like I was young, then I step in front of a mirror and see reality.

Dan

My mirror does silly things like that too. I haven't been able to find a mirror that works properly!

Fred