This was written for the average Mark II owner that doesn't have all the information they need to make informed decisions.
In my opinion, unless you're barreling down mountain passes, or driving in water up to you floor pans, I see no other good reason to install disc brakes on a Mark II.
I started doing brake jobs at my Uncle Milt's Standard station at the age of 14, in 1966, to pay off a debt my parents knew nothing about. While they were on vacation I "serviced" my mother's '63 Tempest and overfilled the trans-axle and left the dope out of the differential. My father worked out of the house, and got rid of us all during the summer by joining a swim club 25 miles from our home. On the first trip after me "fixing" her car the rear end seized up. My father came to get us after calling Uncle Milt for a tow. I rode back with Milt and confessed that I thought I might be the cause. He did a rear axle swap and only charged my parents $100.00. I paid the rest out of wages.
When I went to work for him every Saturday and Sunday I was given many tasks. The first thing I learned was how to use the stud gun for snow tires. Talk about boring. Then I learned oil changes. Oil filters were changed and a new mileage sticker went on every door or post. I then learned brakes. I'd say that by 1966 new-fangled disc brakes started showing up on passenger cars. I kept learning about drum brakes.
Having no experience I was told how brakes worked. In simple terms the friction of the shoe material, which is sacrificial, creates stopping power when it pushes against the inside of the drum (which is sacrificial), by two pistons with hydraulic pressure made by your foot on the brake pedal. The harder you push, the more the friction increases. That interaction of material produces heat, an element of good stopping, but also the ruin of good parts. The brake shoes are stationary, attached to the car, while the drum spins around the shoes on bearings. The drum is attached to the wheel and tire through the lug nuts. The stopping of the tire from rotating makes the whole car come to a halt safely if all the brakes are working evenly. If they aren't the car will pull to one side or the other on hard braking.
I learned that the best brake job consisted of new shoes, new drums, and new spring kits, the last being the most important of any brake job. I'll start there. The braking system on all hydraulic-equipped cars operate the same. Hydraulic fluid is pushed out of the master cylinder under the pressure of your foot. It passes through a rigid brake line, and through flexible hoses to allow for steering and the up and down motion of the rear axle. If you didn't know how old your flexible hoses were, they got changed. They were the weak link of any single or dual MC system. Where the springs come into play is the extremely important task of retracting the shoes so that the pistons that push them out get pushed back all the way into the cylinder, pushing the brake fluid back to the reserve. If the springs are weak and the shoes do not retract they will wear out the drum and shoes prematurely. When heat is produced it hastens the demise of the strength of the spring, so, installing new shoes with old springs is really asking for trouble. I did that to my own car once. The rear shoes wore out prematurely. The springs "looked" fine, but they weren't. I burned up the new shoes and a drum. If the brake shoes do not fully retract, the fluid will be low.
When Mark II drums are new they measure 12", precisely. When shoes are new they fit a 12" diameter drum, precisely. However, while a new drum that has worn .030" it's reusable, but it's 12.030" in diameter and the 12" shoes no longer fit. Take a quarter and put a nickel on top of it and align the right edge of the coins. The difference in arcs explains why you must re-arc the new shoe to fit the worn drum. You can see from that example that by "wearing-in" the shoes you're literally creating so much heat that you're glazing the shoes and drums, losing most of the stopping power. The initial small burned contact patch burns away, making the glazed area bigger and bigger each time you use your brakes. The more you use the brakes the faster you make them worse. Eventually, they do wear into the arc of of of the worn drum, but by then they are too slick to provide much friction without excessive pressure and heat.
In Milt's and Moe's Standard on 8-mile near Wyoming, they had a brake arcing grinder in the back room. They were in the process of being banned in service stations and that often vented the asbestos dust into the alley. Funny how no weeds grew in the discarded dust. We really didn't know. The job of brake arcing then fell on the local machine shop that did automotive work. The machines were pulled when liability insurance and the cost of elaborate filtration systems outweighed the income. However, the airplane and large trucks industry still largely use drum brakes. The norm became shops sending out shoes to specialists. This is how they do it. You take your worn drums to the automotive machine shop. The drums are measured precisely with a special drum micrometer. If they would be within specifications after turning a somewhat coarse surface. A coarse surface will smooth as any corrections are made to the shoe and drum for final arc mating. Then the drum is marked with the measurement of the finished bore. This measurement is what that specific pair of new shoes are ground to fit. The shoes would be marked with the same measurement to tell the grinder what size to trim them to without having the drums in hand. They repeat that for each drum and send your shoes out for relining and grinding. You tell them the kind of car and the weight and its use and they select the proper friction material for the application. That's far better than one-grit-fits-all, off-the-shelf shoes that don't come from the original manufacturer. Now you have the first key elements covered.
While the drums are at the machine shop have them lube new bearings and press in new bearing seats and seals. I frequently find bearings with no grease on brakes that have overheated. They seem to be a case of cause and affect. Bearings are very inexpensive. Like flexible brake lines, if you don't know how old they are, replace them. Talk to camper/trailer owners. There's no worse way to stop your forward motion and ruin your vacation than a spun bearing.
Nobody thinks about lubrication when it comes to brakes. Listen to your brakes in operation. Have someone push on the pedal with the tires off. If you hear anything, you shouldn't. The shoes need to retract freely. If you hear "spring" noises you need to get out the brake grease. Springs themselves don't make noise. What you're hearing is the springs rubbing against their perches. If that contact point were lubricated there would be no catching and no noise. The springs hold the shoes to the backer plates need to be able to move freely as the shoe moves. They move more with wear. The 3 pads that each shoe gets pulled against must be lubed as well as the spring at the adjuster. Anything lubricated that's metal to metal will help the shoes retract properly. You should not need a return spring on the brake pedal.
The brake cylinders, pushing in opposite directions, apply the hydraulic force to 2 pins that push the arced brake shoe lining into the properly-fitting drum. The other end of the shoes are held together with a spring that acts to hold the adjuster in place and to hold the adjustment star in place of the selected setting. That separates the shoes and gives equal pressure to both shoes, if that's desired. The engineers determine if these wheel cylinders need to both be the same size or different, based on trillions of miles of development. That's called brake bias. There are engineering norms that apply. Great study and education goes into shoe bias and front/rear bias. That is accomplish on some cars with a dual wheel cylinder with different size bores. On a Mark II the engineering said 2.5" wide shoes in the front and 2" wide shoes on the rear. Far more friction material on the front than can be delivered with Mustang disc brakes.
I'm not alone in my findings. Many professional mechanics have reversed more systems than they've installed. I have an explanation. Since the common practice of "wearing-in" brakes became the cop-out for mechanics that wanted to get a car off it's rack while shoes were sent out they cautioned the customer to drive gently and everything would be fine. That's really not the case, at all. I wish people had an opportunity to drive on good Mark II brakes before making the decision. Like I said, unless you're barreling down a mountain or driving in 12" of water, Mark II brakes work great. I would hope that those that have done a complete brake job would attest to the success. Driven in a manner appropriate for a Mark II, it's an extremely capable car.
The last item is the Master Cylinder. From what I've seen the Treadle-Vac master cylinder is unique in the realm. A traditional master cylinder has a cylinder bore with a piston and seal, like an internal combustion cylinder that compresses air and fuel. On a normal master cylinder brake fluid fills a chamber. Your foot moves a rod that moves a piston that pushes the fluid out of the chamber ahead of it. That push of fluid is what moved the wheel cylinder pistons outward. The Treadle Vac accomplishes the same results safer. The MC has a reserve of brake fluid, but the pressure is created by pushing a rod into an open chamber causing movement by displacement. The failure risk is lessened by the much smaller diameter seal, and, the fact that any fluid that does get past the first seal is stopped by the second and any leakage is returned to the reserve instead of filling up your booster with brake fluid or on standard brakes have it drip into your feet. The MC works great if you bench bleed it before installation.
There are only two weak links, the aforementioned rubber brake hoses, or rust. The wheel cylinders are iron. They interact great with brake fluid, until the brake fluid absorbs molecules of moisture through the vented master cylinder cap. The surface of the brake fluid in the reserve, which is an oil, is hygroscopic, which means that it absorbs water. Water molecules are tiny and will settle in the lowest part of the braking system, the wheel cylinders and the brake line that runs under the front of the engine. That's the culprit if you can't figure out why you have a pull, or worn brakes on the RH front side. Water brings in the component of Oxygen, which starts to make a mess of your wheel cylinders and can block steel brake lines. Rust blossoms can keep the cylinder from moving, or retracting. I was diligent about 2-3 year brake fluid changes, yet my brakes did fail, spectacularly, so even if you have disc rear you have shoes in the back. In fact, it was my rear brakes that saved our lives.
I was in the commercial lighting maintenance business for 40 years. I sold commercial parking lot owners on group relamping. I changed all the lamps all at once and gave them a discount. It was so bright they couldn't believe it! I gave them a 2 year warranty. When the first lamp that expired out of warranty I sold them another group relamping. The HID lights lights, like brakes, got less efficient over time and usage. They were comparing lamps that were fairly new bunched with lamps that were fairly old and the mix was dim. Installing all new lamps restored the original designed light level and everybody was happy with the arrangement for 40 years. So, people are astounded when I tell them I made my fortune changing light bulbs. They think I'm kidding. Like everything else, operating at peak efficiency is optimum.
Your rear brakes are also your emergency brake, which on many modern 4-wheel disc cars, is a drum brake. :) If your hydraulics do fail you manually activate the brakes through a series of levers and cables that give you the mechanical advantage close to hydraulics. These are not dependent on the hydraulic wheel cylinders at all, the cable moves a lever that applies appropriate braking, if the brakes are not glazed.
In the end, it's your car. if you feel safer with disc brakes, that's great. That in itself is a plus. If you've only compare glazed or poorly maintained brakes to new disc brakes you actually drawn an inaccurate comparison. My best advice is to seek out any owner with good brakes and swap cars for 10 minutes in a parking lot. These cars benefitted from major engineering dollars at Lincoln. You owe it to yourself to compare what they can be as new. Most of you are fixing as you go. Those of us with fully restored cars have the benefit of knowing what they were like new.
Does this need pictures?
Glazed and media-blasted shoe. Brake shoes are not supposed to be reflective.
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But brake drums are supposed to be shiny. What you're seeing us burned metal. This is a '58 Chevy I'm working on. He replaced the shoes without arcing the shoes to match.
Attachment 23675
