We should note a couple of important points at this stage.

First - if you look closely you will notice that the spindle area where weld-on disc brake bracket will be installed (labelled "D" in the above pic) is not perfectly round, but actually very slightly tapered being larger in diameter on the outside and slightly decreasing towards the outside (end) of the spindle. So what? Well, this is going to add to the challenge of getting the bracket perfectly square to the axle. And we know the bracket must be square (as well as the holes perfectly spaced and true) otherwise every press of the brakes twists and bends stuff until something (or everything!) goes BOOM!

Now, to be fair, even a 3/8" thick bracket doesn't really have enough surface area on the inner radius to be relied upon for proper indexing square to the axle, but the fact that the spindle area is neither perfectly cylindrical nor exactly 3.25" in diameter adds to the challenge of getting the bracket square and true which, trust me, is very important. We'll return to this topic and how to deal with it momentarily, but for now, let's take a look at another option should you not want to mess with tricky alignment or even weld.

Bolt-on Brackets

If your 14-Bolt still has the original stock drum-brake backing plate brackets, there are options for bolt-on brackets. These have not-only the advantage that you don't have to grind and weld to install disc brakes, but also they automatically position the bracket, and therefore the caliper in the correct position (both height over the rotor and spacing laterally on the axle).

Weld-on Brackets

If you don't have an axle for which there is a bolt-on bracket available, or if you want the lightest or cleanest installation, or like me, you no longer have stock flanges to bolt to, then you need to use a weld-on bracket.

Hubs

Callipers, Pads, and Rotors

Most places, you will read that the callipers, pads, and rotor required can be sourced from 1972-1986 Chevy 3/4-ton trucks (rotors, pads, callipers) and 1972-1986 Chevy 1/2-ton trucks (pads & callipers).

While that is a true statement, there's actually a bit more to it than that, including a larger HD calliper option, a difference between metric and standard brake line fittings, and a huge list of potential application.

Here are the details, BillaVista style:

Callipers

There are actually three different callipers to choose from:

1) Standard front calliper, 2-15/16" Piston, standard 7/16"-NF brake line (banjo bolt) fitting [1971-1978].

2) Standard front calliper, 2-15/16" Piston, metric 10mm x 1.0 brake line (banjo bolt) fitting [1979-1986, 7,200 Lbs GVW, RPO JB6/JD6].

3) Heavy-Duty front calliper, 3-5/32" Piston, metric 10mm x 1.0 brake line (banjo bolt) fitting [1971-1986, 8,400 Lbs GVW, RPO JB7/JD7]

What's this RPO thing?

RPO Codes

GM uses a 3-digit code, called an RPO (an acronym for Regular Production Option), to identify the options with which a specific vehicle is built. They are listed on a label or sticker called the Service Parts Identification (SPID) label. On late-model GM trucks this label is found inside the glove box, on earlier trucks it may be on a door jamb or kick panel. Some of the most famous RPOs are Z28 (performance package found on Camaros) and LS1 (specific type of V8 engine).

By looking up RPOs in a reference table you can identify the options with which the vehicle was built.

Note that sometimes they are referred to as "options codes", "equipment codes", or even specific names such as, in this case, "brake codes".

Now, back to brakes - you will note that, in the description above I mentioned RPOs (aka brake codes) such as JB6 and JB7.

If you search through this master list of GM RPOs, you will find the following definitions for these brake-related RPOs:

JB5: Brake, Power, Disc/Drum, 6,400 Lbs GVW
JB6: Brake Power, Disc/Drum, 7,200 Lbs GVW
JB7: Brake, Power, Disc/Drum, 8,400 Lbs GVW

JD5: Brake, Dual Power, Disc/Drum, 6,400 Lbs GVW (Dual Diaphragm Vacuum Booster)
JD6: Brake Hyd Power, Disc/Drum, 7,200 Lbs GVW (Hydro-Boost Booster)
JD7: Brake, Hyd Power, Disc/Drum, 8,400 Lbs GVW (Hydro-Boost Booster)

Some parts places and / or manufacturers refer to these RPOs or "brake codes" when you order or lookup parts, so now you know what they are referring too.

So, in summary, you can choose to use a standard calliper with a 2-15/16" piston and either standard or metric brake line fitting. Or you can choose a more heavy duty calliper with a larger 3-5/32" piston and a metric brake line fitting (there is no HD calliper with standard brake line fitting). They all fit over the same rotor, take the same pads, and bolt up to the same brackets.

Here are some part numbers for the different callipers:

Standard calliper, 2-15/16" Piston, 7/16"-NF brake line (banjo bolt) fitting.

Fenco Callipers:

Front Left: p/n: C502 / Front Right: p/n: C503: 1971-1978 Chevy K20 4x4 3/4-ton pickup.

Wagner Callipers:

Front Left: p/n: CR76050 / Front Right: p/n: CR76051: 1971-1978 Chevy K20 4x4 3/4-ton pickup.

Standard front calliper, 2-15/16" Piston, 10mm x 1.0 brake line (banjo bolt) fitting.

Fenco Callipers:

Front Left: p/n: C528 / Front Right: p/n: C529: 1979-1986 Chevy K20 4x4 3/4-ton pickup 7,200 Lbs GVW, RPO JB6/JD6.

Wagner Callipers:

Front Left: p/n: CR130212 / Front Right: p/n: CR130213: 1979-1980 Chevy K20 4x4 3/4-ton pickup, 7,200 Lbs GVW, RPO JB6.

Front Left: p/n: CR98886 / Front Right: p/n: CR98887: 1981-1986 Chevy K20 4x4 3/4-ton pickup, 7,200 Lbs GVW, RPO JB6.

Heavy-Duty front calliper, 3-5/32" Piston, 10mm x 1.0 brake line (banjo bolt) fitting.

Fenco Callipers:

Front Left: p/n: C530 / Front Right: p/n: C531: 1979-1986 Chevy K20 4x4 3/4-ton pickup 8,400 Lbs GVW, RPO JB7/JD7.

Wagner Callipers:

Front Left: p/n: CR98954 / Front Right: p/n: CR98955: 1979-1986 Chevy K20 4x4 3/4-ton pickup 8,400 Lbs GVW, RPO JB7.

*Note that all these part numbers are for bare or "unloaded" callipers - meaning all you get is the bare calliper - no pins, no clips, no pads. Most manufacturers also sell callipers that are "semi-loaded" (meaning they include the hardware such as pins and clips) or "loaded" (meaning they include the hardware and pads. Often the part numbers are similar, but with a different refix. For example, "C528" is a standard metric-fitting calliper from Fenco, and "SLC528" is the same thing but Semi Loaded (SL). "CR98954" is an unloaded Wagner HD calliper, "L98954" is the same calliper loaded. But there are no hard and fast rules to this naming system.

Here are some screen caps from the Federal-Mogul / Wagner online parts-finder app showing calliper applications:

Standard calliper, 2-15/16" Piston, 7/16"-NF brake line (banjo bolt) fitting.

Part numbers: CR76050 / CR76051

Standard front calliper, 2-15/16" Piston, 10mm x 1.0 brake line (banjo bolt) fitting.

Part numbers: CR130212 /CR130213

Part numbers: CR98886 / CR98887

Heavy-Duty front calliper, 3-5/32" Piston, 10mm x 1.0 brake line (banjo bolt) fitting.

Part numbers: CR98954 / CR98955

Two final points about ordering parts to keep in mind:

1) It is best to never quote an application on or very near a transition year, if you can help it. Sometimes funny things happen with production runs close to transition years. For example, the standard calliper with standard threads fits 1971-1978 Chevy K20, but I would never quote 1971 or 1978 to a counterman or online ordering system - too much risk. Pick a year in the middle.

2) I do my best to be accurate and complete, but even I can make mistake. Also, companies get bought, sold, re-structured, and change their inventory, part numbering, and other practices. Therefore it's always a good idea to cross check a part number or application before spending money. Fortunately there are lots of good sites with lost of good online data available where you can do your own confirming; such as those at the following links:

Federal Mogul / Wagner

Fenco

AC Delco

Raybestos

Pads

There are a huge number of pads available that will work for this conversion. Obviously the pads matching the application or part number for the calliper you use will work. Also, each manufacturer usually makes 2-3 different types of pads for most of the applications in question. For example, Wagner make at least the following:

• ThermoQuiet OE Semi-Metallic.
• ThermoQuiet Ceramic.
• QuickStop OE Semi-Metallic.
• QuickStop Ceramic.
• SevereDuty

The pads for the standard callipers (metric or standard brake line) are the same. The pads for the HD Calliper are different.

According to the Wagner online data, for their ThermoQuiet OE Semi-Metallic line of pads, the standard calliper pads have Friction Thickness of 0.6" (Inner Pad) and 0.54" (Outer Pad). The same pads for the larger HD calliper have Friction Thickness of 0.662" (Inner Pad) and 0.572" (Outer Pad).

Not having handled or measured the HD calliper pads, I do not know if their are other differences or if they are at all interchangeable so I would recommend you stick with the pads intended for the callipers you use.

Here are some Wagner Disc Brake Pad part numbers (each for set of 4 pads):

Just for interest, here's a list of applications that use the standard-calliper pads. It's ridiculously huge. So - no worries of the pads going out of service anytime soon!

Rotors

There are fewer rotor choices (thank god!) than for the callipers and pads, because obviously only applications with 8-lug axles will use 8-lug rotors that will fit the 14-Bolt axle.

Here are some applications.

Wheel Studs

* Note: Papco list the knurl diameter as 0.630", Doorman list it as 0.622". I measured it at 0.620" - 0.625". I'm going to use 0.625" as an average.

But there are three problems with reusing the old studs from the original drum setup.

Compared to the old drum, the mounting flange on the new rotor hat is thicker and the diameter of the stud holes is larger. The result is: the old studs are too short, the knurled section is too small in diameter, and the knurled section is also a little too short to completely stake the rotor and hub together. So, ideally, we need a stud that is longer and has a longer and larger diameter knurled section. Let's take a look at the numbers

Looking at the numbers (bold text), we can see that there's another problem. While the stud hole in the new rotor is larger, obviously the holes in the hub are not. Therefore, if we used a stud with a large enough knurl diameter to fit snugly in the rotor hole, it wouldn't go through the hole in the hub.

So, we have three options:

Option 1:

We could find the closest suitable stud and have the holes in the wheel hub machined out to the same diameter as the rotor holes. Since the rotor hole is 0.658" and we are staking the rotor and drum together, we need a class V interference fit (press fit) which necessitates a knurled section 10-20 thou larger than the hole - as is the case with the stock stud which is about 17 thou larger than the hub hole. So we'd need a 9/16-18 stud, at least 3.5 long, with a knurl diameter of between 0.668 - 0.678, and a knurl length of at least 0.75".

So this stud has the right thread, overall length, and the critical knurl diameter. But the problem is the short knurl length, short shoulder length, and the positioning of the knurl right up under the head.

This means the knurl would be a nice tight fit in the rotor, but there would be no knurl length to engage the hub - not good for staking the two together and certainly not worth machining hubs for. Also, the shoulder itself is pretty short and would only go into the hub hole by about a 1/4" or so. And to top it off I wouldn't be crazy about the small head sitting in the recess on the back of the rotor.

So - scratch option 1 - too much work and expense to machine the hubs for what would be a lousy solution in the end anyway.

Option 2:

We could find the closest suitable stud and have it machined or custom studs made to the required specifications.

I discarded this option right away as being too expensive and impractical. To start with,in order to machine a stock stud, you'd have to start with one with a knurl diameter large enough to be a press fit into the rotor hole - and the only one of those is the one we mentioned above and it wouldn't work well for the reasons we already discussed. The only other option would be to start with a long-enough larger stud like a 5/8-18 that has an appropriate knurl and shoulder, and have the threads re-cut. Only two problems: 1- there aren't any and 2- in my opinion, re-cutting the threads from 5/8 to 9/16 is not a good idea on something that has the nuts on and off, and as tightly, as wheel studs. That leaves having completely new custom studs made - which has three problems: 1- How many places are able to do that? 2- It would be expensive, and 3- you would still be left with a major design flaw, namely that there would be a radius change in the stud (and therefore a natural stress riser) right were the shear-plane is between the rotor and the hub. As my old hero Carl Smith would succinctly say - dumb!

Option 3:

There are two possible studs that might fit the bill here, neither of them perfect, both with their own drawbacks (actually three if we consider metric equivalents, but let's just focus on the standard-thread choices and look at the metric option later).

So, this stud has the right thread, and the knurl is a good diameter to fit snugly in the hub hole. Also, the smooth shoulder between the underside of the head and the beginning of the knurl is about 0.7" in diameter - making it a good snug fit for the hole in the rotor (about 10 thou larger than the hole). The problem is the very short length of the knurl and its position on the shoulder.

And the problem with that is, it puts the stud at pretty good risk of spinning when the lug nuts are done up or removed - especially since the fit between the shoulder and the rotor is smooth and not knurled.

So the stud is good for centering the hub and rotor together with the two different size holes, but it's hardly ideal since it essentially trades a poor fit in the rotor (stock stud) for a poor fit in the hub. Plus, at only 3.25" long, it's really not quite as long as we would like.

So that brings us to the final option, and the one I chose.

So, this is the best compromise in my opinion (or at least the least objectionable). But it does leave the problem of the rotor being sloppy on the stud, which means that as you drive the studs through the rotor and hub, it can be difficult to maintain the rotor perfectly centred and aligned to the hub. Here's a video that shows the issue:

Not great, but not the end of the world either.

Now - before we move on, there is just one stud to look at - the metric one I mentioned earlier.

It is essentially the metric version of the previous stud, used in later-model versions of the same trucks, as metric parts began to creep in more and more.

It can be found in the following applications:

1988-1998 Chevrolet C3500 2WD 1-Ton Pickup with DRW & Drum Brakes

1988-1998 Chevrolet K3500 4WD 1-Ton Pickup with DRW & Drum Brakes

I ended up actually using this metric wheel stud since the local parts place didn't have any in standard-thread and I was in a hurry.

Wheel Nuts

In case your needs, design, or wants differ from those that I've described in this article, you can always browse the following catalogs for different options for wheel studs and wheel nuts.

Dorman Wheel Studs and Nuts Catalog

Papco Wheel Parts (Hardware) - 2009 Catalog

Putting it all Together

OK, so now we have all our parts choices made, it's time to complete the project.