Some of you have asked about the rear disc brakes for your Bronco’s. Below is a summation of about 5 years worth of research and experimentation with 2 totally different rear disc brake systems, both of the original FORD equipment on their respectitive vehicles. This is no way comprehensive and is my opinion and experiences and should be treated as such. Most, if not all, the facts can be checked if you wish to follow up on this.

I have used two different rear disc systems on my 2 Broncos.

One system came from a 1973 Ford Thunderbird car. This was the “Big Bird”. As I recall the car was a sick green and had four doors and was a real boat. My shock came when I found rear discs on this car. Digging discovered that the brakes were available on this car at this time. The option only lasted for about 5 years so if you find one with it on it. GRAB IT!! If you don’t want it let me know I will buy it. For obvious reasons, I call this the Bird conversion or something similar. It was on a 9” rear end with the small bearings and the small bolt pattern. Keep this in mind when you are hunting for rear discs as it is critical.

The other system came from a 78 Lincoln Mark Car. Again, a real boat, white in color and had all the options, (except hydroboost which was strange). Big four door SOB and just about bent my Jackall getting the thing up into the air. Some Lincolns had rear discs, and if you get a chance to get this setup go for it. You will NOT find this in a U-Pull yard. These are long gone from these cars before the wreck even hits the yard. The hot rodders have this market sewn up and the yard guys are in their pockets. You will find this setup on cars out in the boonies; behind the barn type discoveries so to speak. I found mine this way. Bought the car for 100 bucks and made money by the bucket load on the car. That is another story. This is the desirable system as it has big calipers and rotors. This is also a 9” rear-end with the big bearings and large bolt pattern. I call this system the Mark conversion or something similar.

Now to the basics. On both systems, when you are stripping the brake systems out, take everything. All the little clips, hoses, brackets, clamps, brake fittings, Ebrake cables and lines that is attached to the system. Get the Master Cylinder and Proportioning valve or Hblock depending what is on the car. If you forget or don’t get one little item and go to buy it at the local parts store, you will learn what sticker shock is real quick. If it is attached connected or remotely part of the brake systems take it.

There are two different types of rear discs, one is called floating caliper and the other is called sliding caliper. Most of you are familiar with sliding as that is what most front discs are. Obviously it is because of the way the calipers function that the systems work. I have had both. The bird conversion was floating, the Mark conversion is sliding. If you want to see the two different systems get the Hayes manual for the Big Mercury cars in the 80 to 90 years and it is illustrated there. I have 2 of these manuals and they are very thoroughly explained in these manuals. If you are going to do rear discs get one of these manuals, the reference is worth the price.

The Bird conversion is usually floating, do not be afraid of this, it works very well. The discs are about 11” in diameter and are unidirectional. Grab the discs for a Bird conversion. If you have time and the energy get the front disc system, all of it. Even though the caliper mount may not work you will be glad you did get the rest if you get a brake imbalance condition in your Bronco. Simple exchange of the fronts fixes this very quickly. This system is easy to install and magnifies the rear braking power by many factors. It really shines on rock crawlers, mudders and people who like to swim with their Broncos. If it gets wet, the rear discs will save your ass more times than not. Decent size discs, easy to maintain and not expensive to buy.

The Mark conversion, this one is the big one. If you get monster meats on your rig or love to get into the deep and dirty stuff this is the one you want. The Mark conversion is always sliding caliper. I have never seen a floating caliper on a Lincoln. Not saying there isn’t one, just I have not seen it. Again, as above, grab all the parts off the brake system. If you have time and energy get the front discs calipers and mounting hardware. If you have problems with your system you will be glad you did this. One exception with this one, unless the rotors are new or near new, don’t bother with them. They are unidirectional and very expensive. This is to say that each rotor is labeled, one left one right. There are better replacements for this system. I have seen the Mark Conversion with 13” rotors!! This is serious stopping power. This system usually has hydroboost attached to it. If you get anything, get the hydroboost unit then get the discs. Most Mark conversions are on 9” rears big bearing big bolt pattern. Check the rear end, some Lincolns came with Detroits in them. Don’t leave this behind!! Again, bolts on to a big bearing rear-end. The replacement rotor that usually works is a Jeep rotor off a CJ7 or something like that. I have a parts guy running down the details now but we both seem to agree the front discs off a 78 ½ ton 4×4 pickup should fit into the rear as the calipers are the same size. The pistons in the calipers are even the same size. More on this later as this is assumptions on our part and we are still looking into this.

I have run the Bird conversion on a 1968 Bronco and it worked well. 6 cylinder with manual brakes and the system had no problems locking up the 31 inch rubber on the truck. Bear in mind this is with the Birds MC and Hblock not the Bronco’s. great system worked well and gave me no grief.

I am presently putting the Mark conversion on my 73. This one has a 355 going into it and has 33” M&T’s on it. I will keep you informed on this one. Have a major problem with mine, it was born with the small bearing rear-end and I have to decide whether to alter this rear to accept the brakes or get a new big bearing rear-end. As my present rear has a Detroit in it and works great I am leaning to altering it accept the discs. I have altered another Bronco to the Marks brakes, it was a 77. Worked great with the jeep rotors. Was a bolt on and he has had no problems with the setup. He loves taking it to Midas for a checkup and watching the ‘technicians’ go nuts trying to figure out where to get the new pads for the rear discs. After the pad episode they are really stuck when they cannot figure out the rotors. (The mark rotors are really different appearance wise than the Jeep rotors) He lets them run around for a while and then tells them to “forget it, I will change them tomorrow”

Why the Bird or Mark Conversion?? It is all FORD. No welding, No adapting, no screwing around. It either fits like a glove or it will not fit, no way. The rear disc e brake system works. Most conversions do not allow for this. These conversions the emergency brakes work period. I am lazy; I will not reinvent the wheel when someone else already has done it. If it is bolt on, it’s for me. Get my drift?? It works all the way not just part way. These are the only way to get fully functional rear discs for your horse. Not that other kits are bad, just a lot of work, or incomplete, or both. Also parts are readily available and relatively inexpensive. Worst case is a FORD dealer but he is still cheaper than some of the aftermarket kits.

Get the FORD version and get it stopped quickly. These conversions are out there and cheap if you look right. GO FOR IT!!

Tech article by TOFIC (The Old Fart in Canada.)

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The addition of rear disc brakes is a popular upgrade for early Broncos. Lots of creative people have accomplished this mod using components from Lincolns, Cadillacs, Ford Explorers and others. These days it’s easier than ever due to the availability of commercial kits that include everything needed for the swap. Generally the kits are an adaptation of parts obtained from vehicles which came with them from the factory, most often based on a GM caliper found on 1980’s vintage Cadillacs, Buicks and other GM luxury vehicles. The piston area of this caliper is a good match for the stock Ford calipers found on ‘76-’77 Broncos and F150s as well as the calipers used by Bronco enthusiasts for the Chevy front disc conversion. This GM caliper also incorporates an emergency brake mechanism that matches the cables found on early Broncos perfectly.That emergency brake mechanism doesn’t always work as it should, however, particularly if the calipers came from a junkyard donor vehicle. When I first did this swap, I could find no information on how the emergency brake mechanism worked, and as it turned out, mine didn’t work at all for a while. I had been told that I needed to cycle the emergency brake to adjust the calipers, which I did until my foot was numb. That didn’t work, so I started experimenting with the calipers, taking them apart to understand how they worked. In this article I’ll explain what I learned, and how to make those bargain junkyard calipers work as expected.

DISCLAIMER: Bad brakes can kill you. If you choose to rebuild your brakes, it is your responsibility to ensure that quality parts and good shop practices are followed in every aspect of the brake system. The follow information provides guidelines on servicing Cadillac rear brake calipers only, and is not intended to be the last word on brake system design and repair. I won’t be held responsible if you make a mistake. Honestly evaluate your abilities to perform brake system diagnosis, service and modifications before touching them, and hire a professional mechanic to do the job for you if you aren’t certain you can do it yourself. You, your passengers and your loved ones will be better off.

First, a photo with some terminology- I need to call the components something for explanatory purposes. These are my choices for names- GM may have used something else. The picture shows a right side caliper (note the “R” on the casting) straight from the junkyard.In a conventional disc brake caliper, the piston is advanced out of its bore as the pads wear. There is no mechanism that retracts the piston when the brakes are released, so it and the pads remain in light contact with the rotor at all times, ready to clamp when required. In the GM caliper, things are different. When the brakes are applied, the piston is forced out of its bore as always, but the parking brake mechanism inside the piston actually causes it to retract when the brakes are released. Instead, the GM caliper does indeed depend on the regular use of the emergency brake to advance the piston and remain in adjustment. When the emergency brake is applied, the lever is rotated, which causes the threaded shaft to drive the piston out of the bore and clamp the pads against the rotor. When the emergency brake is released a “one-way clutch” built into the piston slips, allowing the piston to remain extended while the clamping force is released.

The problem arises when that mechanism seizes. In the case of mine, I got them cleaned up, installed, hooked up the brake lines and bled like crazy. Tried the brakes, pedal went to the floor. A couple of pumps brought it up, but nothing I did could get a good pedal. Eventually I figured out that if I re-clocked the e-brake arm by removing it, rotating the shaft until it clamped the pads against the rotor and re-installing it angled as far back as possible, I could get my brakes to work without pumping so much. But using the e-brake still didn’t make any difference. So I bought a rebuild kit from Napa (expensive at $30 per caliper) and proceeded to dismantle it. The caliper I used for the photos here was a spare, so rebuild parts aren’t shown. If the caliper is in generally good condition (piston dust seal not ripped, no leaks) then a rebuild kit may not even be necessary, though some peace of mind comes from knowing that all the rubber parts in an otherwise 20 year old caliper are in good shape.

Remove the 11/16″ retaining nut and wiggle the e-brake arm loose. There should be a rubber seal and a nylon washer under the arm. Remove those and set them aside (there are replacements in caliper rebuild kits). Once the arm is off, give the end of the actuating shaft a nudge and the piston will pop out, followed by a big spring. Along with a bunch of smelly old brake fluid.

Note the hex on the actuating shaft. This actually measures out to 0.55 inches, but a 9/16″ wrench will turn it. The piston dust seal can be pried out carefully using a screwdriver. No need to remove the cable bracket- I’ve taken off a couple of them, but there is Loctite on the threads of the Torx bolt, so they are tough to get loose unless you heat the caliper bracket first in the vicinity of the bracket.

It can be seen that the actuator shaft from this caliper has a right hand thread. On a left side caliper, it’s the opposite. The brass washer on the shaft is important. It’s a bushing that presses against the inside of the housing to react the load of the shaft trying to force the piston out when the e-brake is engaged.

Now we come to the interesting part- disassembling the piston. The caliper used for these photos was in pretty good shape, but the piston assemblies in the calipers on my Bronco were gummed up and corroded. Most people never bleed their brakes regularly to renew the fluid. Brake fluid absorbs water and anything else it can from the environment, and eventually it corrodes metal parts. In the case of these calipers, it eventually locks up the adjuster mechanism.

To disassemble the piston, I clamp the end of it, the part that sticks out of the dust seal, in a vise. Then I use a pair of water pump pliers to carefully twist the stamped steel retainer out of the piston.

A bit blurry, but this is what’s visible after the retainer is removed. All of the parts can come out, including the plug at the bottom with the female spline. If it’s reluctant, it can be pushed out by inserting a small rod or punch through the hole in the face of the piston.

And finally, the piston and its contents laid out on the bench. It’s important that the three balls captured in the round plate be able to rotate freely. If they can’t the clutch mechanism won’t work- it functions by jamming when a load is applied (when the e-brake is engaged) but allows everything to rotate freely relative to the piston when the force is removed. So clean those bits well before reassembly.

After cleaning and reinstalling the parts in the piston, I pushed the retainer in by hand. Then I squeezed the thing in my vise until the retainer was sticking out of the piston by 3/8″.Now it’s time to install the piston back into the caliper. Spin the actuating shaft into the piston and seat the spring against the retainer. With the caliper clamped in a vise, push everything into the bore until the threaded part of the actuator shaft emerges from the hole. That spring tries hard to shove the piston out of its bore, but once the piston is pushed past the o-ring seal, it tends to stay put. Install the nylon washer and rubber seal over the actuator shaft, followed by the e-brake arm and the retaining nut. The exact clocking of the e-brake arm doesn’t matter at this point. The piston dust seal comes next. It’s easier to do if the piston is sticking out of the bore about 3/4″ or so. If you pushed it in too far, now is when you get to see how the clutch mechanism in the piston works. Cycle the e-brake arm back and forth and it should gradually “pump” the piston out of the bore. Install the seal using a blunt instrument (I used the handle end of an old toothbrush) and slide the lip down until it seats in the groove on the piston.

The next step is to bottom the piston in the bore and orient it correctly. See the notch in the face of the piston? It engages a square bump on the back of the brake pad. That keeps the piston from rotating when the e-brake is applied and released. It needs to be oriented a particular way, as shown in the photo.The tool in the background is for rotating the piston. It’s designed to fit on a 3/8″ drive ratchet. It has a square bump on the face to engage the piston notch, and a a raised boss in the middle that goes in a depression in the middle of the piston, to hold things in alignment while turning. Rotating it also retracts the piston, as it drives the piston up the actuating shaft. When doing this sometimes the piston bottoms before the notch is oriented correctly. Cycle the e-brake arm a couple of times to drive the piston back out a bit, then repeat.

Here’s a photo showing the piston retraction tool in use.

Well, sometimes that tool just won’t work as advertised. If the caliper has been around the block a few times (most have) the notch in the piston may be rounded off, in which case the tool slips no matter how hard you push down on it while turning. In that case, I use my secret weapon.From the looks of the piston, I wasn’t the first to use this procedure.

Once the piston is retracted and oriented correctly, pop the dust seal (yellow plug visible in some of the pictures) into the hole in the face of the piston, assuming it was still there when you got the calipers. If you bought a rebuild kit, you got a new one. The brake pads can then be fit to the caliper. One thing not shown here is a wire spring clip that fits in the groove at the top edge of the piston. It’s an anti-rattle device for the inner brake pad. The spring was there when I got the caliper, but went sailing into the thorn bushes when I bumped it while taking the caliper outside to brush off some of the dirt. It’s still there. My thorn bushes don’t like me and it will take more than the loss of a clip to get me to wade into them again.

That’s it! The caliper is now ready for installation. Once mounted on the vehicle, cycle the e-brake arm a few times before connecting the cables in order to advance the piston out and get the pads in contact with the rotor. If you bought a kit, follow the directions supplied with the kit to complete the installation. In general, disc style emergency brakes don’t work as well as drums, due to the latter’s self-energizing nature. But mine hold well enough with 35″ tires to keep my Bronco from rolling onto the street from my sloping driveway, and of course now my rear brakes stay in adjustment. Most importantly (why we install rear discs in the first place) my Bronco stops straight and true, rain or shine, in the dust, or after water crossings.Tech article by Lars Pedersen (Lars)

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