Converting drum brakes to disc brakes

[wheikkila]

One thing I think we all can agree on. Is brake maintenance is the one item that can't be ignored. I have had people mock me for replacing brake hoses on every car I have purchased. After having a hose bust on you. You never take someone's word I have replaced them.
                 Thanks Wayne       

[TJ Hopland]

A dual master with a line failure is a false sense of security. The peddle will go very near to the floor with only enough braking to stop while rolling, then you better have plenty of room in front. Unfortunately, I speak from a lot of experience, just a word of caution.

Fair point that a line failure on a dual system isn't just a slight reduction in performance, it could be pretty significant but usually at least for an application or two you do still get some brake action. I would think most people that drive older cars in the rust belt have got to experience that a time or three, I know I have.  But are you saying given the choice of no brakes or some brakes you choose none?

I have had failures on singles but luckily not 'on the road'.  Its been on cars that are just being moved or moved onto a trailer sort of a thing.

[signart]

Fair point that a line failure on a dual system isn't just a slight reduction in performance, it could be pretty significant but usually at least for an application or two you do still get some brake action. I would think most people that drive older cars in the rust belt have got to experience that a time or three, I know I have.  But are you saying given the choice of no brakes or some brakes you choose none?

I have had failures on singles but luckily not 'on the road'.  Its been on cars that are just being moved or moved onto a trailer sort of a thing.

Not saying that, but saying you have next to nothing, so just cautioning and encouraging more reliance on maintaining the complete system that you already have or install, including the e-brake to supplement in case of a catastrophic failure.

Luckily our old 50's Caddies, have a reliable 4 speed trans than can be of assistance in a hopefully in a rare instance, and I haven't had occasion to rely on it in my '53 thankfully. But, I have overheated the brake shoes on another GM make on a steep winding downgrade where a two speed gearbox landed me in trouble and had to rely on the overheated emergency brake to come to a complete stop once I got to a short landing. I could not continue my decent from there and had to be towed the rest of the way down. (Thanks, Hagerty)

I hope I don't sound argumentive, I am sincere in my advice and just put in my 2 cents.

[Cadman-iac]

  If done properly with a proportioning valve, and it's in good working order, on a dual system, if you have a line or cylinder failure, the valve will move to close off that half of the system, leaving you with the other half to control your stop. Granted, half, especially the rear half, is not as ideal as the front half, but is still better than nothing.
Back when I was still in the army and running around in a 56 Chevy wagon, I had added a set of overload coil springs that used a big U-bolt to mount them on the axle, and over a period of around a year, one had rotated slightly, (due to vibration I'm guessing), but it caused the brake line to crack eventually and I only discovered it as I was rapidly coming up on a red light. Thankfully it hadn't broken the line off completely, so I was able to pump the pedal until the car stopped, but after I got out to check the fluid in the master, I found I had pumped the thing dry, and I had sprayed brake fluid all over the bottom of the car.
Whenever I convert from a single to a dual system, I always use a proportioning valve and I wire in a warning light so that it can warn me of any problems that may arise. Because usually these problems creep up on you slowly with a small leak. The sudden failure is less likely if you're checking things regularly and fix any seepage that occurs.
A small leak will still allow the system to function, albeit not as effectively, until the fluid runs out in the master cylinder. But if the leak is large enough to cause the proportioning valve to block off that side, it will notify you by illuminating that warning light, and hopefully give you a chance to keep things under control.
  No system failure is ever good, and no system is 100٪ failure proof, but the dual system with a proportioning valve is definitely better than the single circuit brake system with nothing to stop a failure from completely eliminating any brakes you had.
  Also, if I remember correctly, when GM went to the dual brake system, initially it did not include any proportioning valve in the system at all. A dual master cylinder will work with a 4 drum system  just fine without the prop valve, until you have a failure somewhere. Then you loose everything, just like you would with a single system.
  My dad and I had parted out a 66 Cadillac when I was still in school, and I remember that it didn't have any proportioning valve on it at all. Just 2 lines coming out of the master cylinder and going directly to each end of the car. The only connection between the two halves of the system was the master cylinder itself.
When GM began offering disc brakes, there still wasn't a true safety proportioning valve in the system. There was a residual pressure valve on the front supply line that also doubled as the distribution "tee" for the front wheels, but it's only purpose was to keep the required 2 to 3 psi in the lines to prevent the pads from backing off of the rotors.
This was used through at least 1969 that I know of. This is what was used on my 69 De Ville, and every one of the parts cars I had for it as well.
A true safety proportioning valve for disc brakes came along sometime in the early 70's. My 72 Coupe Deville and my 72 Eldorado both had one.
You can tell if you have one by whether it has an electrical connection on top for the warning light.
  Relying on the emergency brake might work for you if it's easy enough to release once applied, but if the release method is complicated and requires you to use a foot to apply and a hand to release, requiring you to coordinate that and still steer the vehicle in the process, it could be more than difficult in a panic situation.
And yes, I know that Cadillac used a vacuum release on the emergency brake if the vehicle is in gear, but if the release valve does not work and you have to reach under the dash to grab the manual release lever, all while trying not to run over someone or something,.... well, you get the point.

Rick

 PS.  I also remember that on a 68 Caprice hardtop with disc brakes that I had once, (and a big block), it did not include any proportioning valve, just a residual pressure valve located just below the master cylinder in the line to the front wheels.