The following article outlines the procedure I followed for swapping rear disc brakes on my rear axle which is a GM Corp 14blt full-floater from a 1979 K30.
Many people have asked me, “Why do this?” Well there are a couple of universal reasons;
- Eliminate the problem of having mud packed in the drums.
- Remove 100+ pounds of weight from the rear axle.
Aside from those I had a couple of personal reasons;
- My rear brakes were pretty much non-existent – as you will see in some following pictures.
- Maintaining disc brakes is much easier.
If you are reading this article and doing research to do this swap yourself, then I’m sure you’re very familiar with what the rear drums on the 14blt FF axle look like. However, it just does not seem right not to have at least one picture of these big, burly brutes in their full glory.
As the picture above illustrates, the first step is to put the rear axle on jack stands and remove the wheels.
Next remove the axle shafts. This is done by removing the eight (8) bolts from the hub with a 3/4″ socket. They are on there tight and use serrated flange bolts, so make sure you have good leverage. Be prepared for fluid to drain out of the hub after the axle shaft is removed.
This is what the hub will look like now.
The hub on the rear axle is very similar to front axle hubs. There will be 2 spindle nuts with some sort of retainer in between. You will need the appropriate hub socket to remove the nuts. On my axle before remove the outer nut I had to bend the tab back from one of the recesses in the nut, otherwise you can’t get the socket on the nut.
- Remove the outer spindle nut.
- Remove the retainer washer.
- Remove inner spindle nut.
- Remove inner keyed washer.
Now you can pull the drum off. Be aware, they are very heavy so have a good grip and position yourself to be able to safely remove them without straining your back.
You may have a situation where you just cannot get the drum to pull off, like maybe you forgot to remove something. Unfortunately it’s not quite that simple. More than likely the shoes have worn into the drum far enough that a lip has formed on the inside of the drum. This lip is preventing the drum from sliding off the shoes. I had this problem on one side. You must back the adjuster off to allow the shoes to move in. Refer to the picture below:
- Yellow finger is pointing to the adjuster – puts tension on the shoes
- Green finger is pointing to the adjuster ratchet stop – keeps the adjuster from backing off
- Red finger is pointing to the access hole for the adjuster
Because what I’m calling the “adjuster ratchet stop” keeps the adjuster from backing off, you need to disengage it in order to move the adjuster the correct direction. All of this must be done through the little access hole. Now I don’t know if there is a fancy tool for this, but I used a long, skinny punch to push the stop away (as you are laying under the truck this means towards the end of the axle) and a flat blade screw driver to turn the adjuster. Yes it’s a big pain.
Now hopefully you have the drums removed and you should see the working components of the drum brakes as seen in the picture above. This entire assembly can be removed in one piece. Remove the four bolts you can see already missing in the picture above. Disconnect the brake line from the back of the assembly and it will just pull off with a little effort. The picture below shows what you’ll have after the removal.
You will see the spindle is welded to the axle tube. I would imagine you’d want to take great care not to damage the spindle because I don’t think replacement will be a simple matter.
Now we are ready to install the disc brakes. I’ll start with a list of the parts you will need:
- Caliper Brackets – mine are from Ruffstuff Specialties and the following parts are what’s needed for these particular brackets. Verify what parts are needed for the brackets you choose.
- Dana 44 Calipers for 73-77 Chevy trucks, 1/2ton or 3/4ton. If you get “loaded” calipers, new pads will be included.
- Rotors for 73-77 Chevy trucks front axle, 3/4ton only
- Rubber brake lines to fit the calipers. There are many options here, the most common are 73-77 Chevy truck application or 1980 Chevy Chevette application (these are popular because they are shorter).
- Brake fluid
- Optional items:
- Proportioning valve – You may find your rear brakes lock up much sooner than the front. This can lead to unstable handling under emergency braking. Installing an adjustable proportioning valve in the rear brake lines will allow you to adjust the bias back to the front brakes.
- New bolts to mount the caliper brackets: Grade 8, 1/2″ x 1″ NF w/split lock washers – 4 per side
- New hard brake lines. They are 3/16″ lines and you can choose from assorted lengths at the parts store and bend them to fit how you like.
- New oil seals for the rear hubs. You have the hubs off, might as well replace them.
- New axle shaft flange gaskets. They are only $3ea, might as well replace them too.
Let’s start with finishing up the last detail in the deconstruction phase. The drums need to be separated from the hubs. The picture below shows where the two pieces separate:
In order to do this the studs must be press out. If you don’t want or need to salvage the existing studs, you can remove them with a big hammer. However, if you plan to re-use them you need to use a press. The “cheap” Harbor Freight press I used worked just fine.
Now the rotors can be attached to the hubs by pressing the studs back on. The rotor installs on the hubs just like the drum was. With that done, it’s time to go back to the axle.
The next step is to install the caliper brackets on the axle. I used a little thread locker on the ends of the bolts and installed new bolts with new lock washers. I orientated the brackets so the caliper will sit as it does on the front axle.
The hub rotor assembly is installed next. The following is the procedure outlined in my Chilton’s book.
- Install the thrust washer
- Install inner spindle nut and torque to 50ft-lbs while rotating the hub. Loosen the nut and re-torque to 35ft-lbs and finally loosen the nut 1/4 turn.
- Install retainer washer
- Install outer nut and torque to 65ft-lbs.
- Bend one tank into the slot on the outer nut.
Install the axle shafts and torque the flange bolts to 115ft-lbs.
Now the caliper can be installed on the rotors. This procedure is the same as installing them on the front axle with the bleeder screw pointing up. Once the caliper is installed attach the rubber brake line. The rubber brake line can then be plumbed in with the hard line. I ran my lines over the top of the springs and along the axle truss. This way they are up out of the way.
Just for curiosity sake, here’s a picture with drums on one side and discs on the other.
Bleed the brakes, install the wheels, and you are done with the install. Now go out and test drive.
As I stated earlier, you may find it necessary to install an adjustable proportioning valve for the rear brakes. I am fortunate and my brakes function properly without one. It seems to be one of those things that differs from truck to truck. It may even come down to personal preference.
I had an opportunity to test the new brakes on a snow, slick trail the day after the install. The brakes worked great. A lot of that probably owed to the fact that my rear shoes were virtually gone and therefore I didn’t have much in the way of rear brakes with the drums. I can tell the brakes are better because I found myself stopping much more suddenly given my usual pedal pressure.