The Stovebolt Site Forums The Shop Area Engine Shop Single to Dual Master Cylinder

I have a 53' Chevy 3/4 ton that currently has a single master brake cylinder. That cylinder is shot, so I am planning on replacing it with a dual master cylinder.

I see that the normal retailers have adapter brackets like this one at Classic Parts.

Are these usable on a 3/4 ton or is it 1/2 only? Also, is buying a bracket like that one my best option, or is there a better/cheaper alternative?

Thanks!

Build Your own , it is not hard {look at the pic} and all You need is some 1/4 inch plate , get the new master from NAPA or Your flaps for a 60s -C20 pick up with drum -drum and build the adapter to fit Your truck. thats what I did and it came out great .



Pete

HERE's a drawing I used a few years back to make an adaptor...Joe

Having a dual master seems like a good idea, one which I had thought about. However in a recent issue of Smoke Signals the magazine of the Pontiac owners club, a professional mechanic discouraged the use. He has been writing a column on rebuilding brakes on older vehicles and says that if the system is maintained properly a single MC will be just as good.
I can't recall the gist of the article but one comment was about his experience when the rear brake line broke and he was unaware of driving with just the front brakes in operation. Perhaps someone here has the article and can quote from it.

Find that hard to believe!... single circuit brakes are better than dual circuit??
I've driven a truck with only the front brakes when the rear ones failed, and I sure knew the difference, like plan stops a block ahead of time.

He is correct in saying that the original system in reasonable shape will give no problems, if it's in good shape it will work fine, by definition. It won't always be in perfect shape, and the brake system still has a chance of failure with the most careful maintenance.

It's the failure mode on single circuit brakes that sucks, you have nothing.
With dial circuit brakes if something fails likely you still have some braking ability; some or even the chance of some is better than none at all.

At least that's how I see it,
Grigg

It's hard for me to believe that a professional mechanic would say not to up grade to a dual MC.
I guess he perfers "NO BRAKES to having "SOME BRAKES"

I can tell you from my own personal experience that having a brake line blow out on a single MC is a more exciting, more hair raising & a hellva lot more dangerous then blowing one out on a dual MC. Ask me how I know

You got to be kidding , He did not know He did not have rear brakes , He never had a brake line bust I had one in My van a long time ago and I'll tell You it a eye opeaner , up grading Your brakes is all about safty for You every one in Your truck and everyone in front of You.I can not understand why anyone says things like that .


Pete

Had a 66 chevelle when i was 18...great little car,except when i blew a brakeline and rear ended this womans brand new peugeot..

I call BS. Did he explain how he was able to maintain pressure to the front brakes with an open line?

Same here. As a professional brake mechanic myself, I most certainly would suggest a dual circuit brake system, especially on a daily/regularly driven vehicle.
I will admit, though, that I did not convert mine, but that was more due to lack of funds at the time I did the brakes. The stock system works fine, but the dual system has that extra safety factor. If I had it to do over, I would go with a dual system, and perhaps a disk conversion (make my own using late model Silverado parts).

First, having taken a few of these trucks apart, I believe the 1/2-ton conversion bracket would work just fine on a 3/4- or 1-ton. The stock frame brackets the adapter attaches to, if not identical, are very similar.

I used the stock porportioning valve from the 'donor' car when I did my disk/dual conversion. I put donor in quotes because aside from the rear axle and drums I used very little of the brake system from the donor, just specified parts for it when I bought new stuff.

The nice thing about that combo valve is it includes a switch that supports lighting an indicator when the dual master goes out of balance.

If memory serves, the switch grounds when the system is unbalanced, so connecting an indicator between an ignition switched power source and that switch means the indicator will light when the two sides are not balanced.

I would quit reading a publication that argued against converting to dual master on anything other than a very limited use show restoration.

One further thought. Dual master became the standard in 1967. Anything with a single master is now at least 43 years old. Unless you are replacing every piece including the lines with new stuff you are trusting you life and those of others on wear and corrosion prone parts more than 40 years old. And if you are not a good proffesional brake installer, ask yourself if you'd bet your kid's life on the work you've done.

A dual master system dramatically increases the odds your brake system will work when you need it. For me I can't imagine ever doing a truck without a dual master conversion.

I have been trying to find a suitable dual cylinder with a 1 1/8" bore size and have so far been unsuccessful. I have read about people using a 67' C-10 dual master, but that has a bore size of 1".

Is it safe to run with a 1" bore size, or is there a vehicle with a 1 1/8" bore size drum setup that I have overlooked?

Thanks

The 3/4 ton MC of that year will have a 1 1/8" bore.

If you don't mind using an aftermarket Corvette style MC from one of the brake kit vendors, they come in many different bore diameters, including 1 1/8". These are the MC the kit brackets are made to support. The aftermarket Corvette style MC also is ported on both sides and can be ordered for stock size fittings or for 3/8-24 fittings. The MC is about $60.

Okay boys and girls I did not make this up. I will dig out those issues and let you know what he wrote. I have an 81 Malibu with a dual master and my rear brake cylinder blew. I drove it for about a week before I knew it. I did know that the front brakes were very sensative and grabbed to the point of almost putting me through the windshield.

Here is a quote from the article. If anyone wants to read the whole story email me and I'll send it as a PDF file.


And here's another
shocker: I would never consider
installing a dual master
cylinder system on the older
cars. Currently, this idea is
being touted in every magazine
as being safer- it ain't. I've had
dozens of those masters fail
TOTALLY on factory equipped
cars. It even happened to me
on one of my own vehicles.
when those dual masters
became standard on the '67
GM cars, I saw a 300%
increase in failures at my own
shop. If you take the time to
maintain your brakes the way
they should be cared for, you'd
never need this so-called safety
net.

Wow, the guy that wrote that article doesn't know much about braking systems, does he? Does he give nay credentials? Like ASE Certification? Sounds like he's the same guy that says there's no such thing as "warped rotors".

But at least you still had brakes........

Was there no change in the pedal feel?

Don't worry to much about what this guy preaches..

He says
"I've had
dozens of those [dual circuit] masters fail
TOTALLY on factory equipped
cars.....
If you take the time to
maintain your brakes the way
they should be cared for, you'd
never need this so-called safety
net [of dual circuit brakes]."

Guess he doesn't take the time to maintain his brake system then does he? A dozen MC failures in a lifetime is several times more that I'd expect anyone to have, but wait.. didn't he say "dozens"?.

With a track record like that wonder how many partial brake system failures his dual circuit systems have actually helped him by avoiding complete brake failures?
With a minimum of 12 complete failures there have to have been some less than complete ones thrown in there too.

I don't have a terribly long driving history, but probably have driven over 250,000 miles in the last 11 years; in used, well used, antique, and some newer vehicles. I have yet to have a master cylinder of any description fail me. I do a reasonable job of maintenance but could do better I'm sure.

I'm still convinced that a dual circuit system is a great idea, and hope I never need that added factor of safety,
Grigg

I totally agree Grigg...How many millions of cars are running these systems....I'll stick with my dual M/C too!

Not to beat a dead horse - I think running a single is OK if you are going for that 100% original ride & changing this could hurt the value.

That said - I can't think of any car or truck I'd drive on a regular basis that didn't have a dual master cylinder. It just makes sense. Not to mention you can buy the entire set up for less than $200 using new parts. If you build your own etc you can convert it for less than $100. No-brainer. They switched to dual cylinders 42 years ago for a reason.

I think the guy in the article is a mechanic & when he says he has had dozens of failures he is talking about the clients he sees not his own vehicles. I too have had a master cylinder totally fail. It sucks. They do however usually give you enough warning to fix it before it is totally gone. The thought of trusting my truck & the lives of others on the road to a single rusty brake line is scary.

Alright, I have the conversion bracket and a master cylinder from a 67' C20 pickup. How much clearance is there between the master cylinder and a SM420 transmission?

I don't have my engine or transmission in and I really don't want to plumb everything only to find out my transmission won't fit anymore.

If anyone has a picture that would be great.

Thanks

If you're refering to the under-cab conversion bracket for installing the master cylinder to the framerail, I've got one installed and would be happy to e-mail you pics.

You send me your e-mail address to [email protected], and I will send you back some pics today if you want.