While all the ’70s and ’80s favorite lowrider GM models will always be long and cool, what’s not-so cool on them are the hideous-looking rear drum brakes. Though these big body styles do come with front disc brakes, it’s sad that the rotor and caliper technology stops right there. As ugly as they were, they performed just as bad.

Moving on to present day, you don’t have to live with that. There are aftermarket conversion kits that will help you convert from a drum to a disc, but if those setups are a bit too pricey then you can always do a Frankenstein conversion by transferring parts from another year, make, and model that has disc brakes. So is it really that simple? Yup … but it will require that you have some basic mechanical prowess, a few tools, as well as the patience to source the parts.

General Motors automobiles have thousands of interchangeable parts. From interior to exterior parts, there’s a plethora of options to choose from, and the same goes for rear disc brakes. For instance, when it comes to rear axle disc brakes, a 1996 SS Impala, 1980-1986 Cadillac Seville, 1979-1985 Cadillac Eldorado, or the third-generation V-8 Camaros and Firebirds were commonly fitted with generous rear disc brakes-11.5-inch rear rotors and two-piston calipers. That caliper and rotor package remained consistent between 1988 and 1997, offering a 10-year span of F-bodies from which you could use as a donor to car to get the parts you need to convert your drum over to disc brake.

Interchangeable GM part illustrations of a 1993 Cadillac Coupe De Ville and a 1996 SS Impala in comparison.
Interchangeable GM part illustrations of a 1993 Cadillac Coupe De Ville and a 1996...

The best plan is to find a rear disc brake donor that’s interchangeable like we did for this tech article. In our own research, we’ve found the parts you will see here for as little as $100 at a local wrecking yard. Just so you understand what we are talking about, the rear axle bolt flange on the third-generation Camaro rear axles is the same as the older 10- and 12-bolt GM rear axle housings, so these calipers will bolt onto virtually any ’70s and later 10- or 12-bolt rear axle assembly.

Replacement rotors and pads, even sliders, can also be purchased new at your local auto parts stores. Assuming your car is currently rolling on rear drums, it is critical to include an adjustable proportioning valve somewhere between the master cylinder and the rear calipers. This provides a way to custom-tune the pressure to the rear brakes. This helps compensate for variables such as adding rear discs, tire diameter changes, and ride height. The key is to adjust the pressure to the rear brakes to prevent premature rear brake lockup that can result in a loss of control.

The only other installation issue is the parking brake cable connection that in the interest of brevity we’ll leave to you. As for pads and rotors, there is a world of options, from basic stock replacement parts that cost almost nothing to drilled and slotted rotors and high-performance pads that are still affordable. Perhaps the biggest hassle in mounting this rear disc brake conversion on an early car is pulling the rear cover/pumpkin of your rearend axle to yank the C-clips so the rear axles can be removed. The rest is easy. Very few tools are needed, so follow along as we take a complete set of a 1996 SS Impala rear disc brake assembly and swap it onto a 1993 Cadillac Coupe De Ville drum brake assembly.

gm model drum to disc brake conversion 1996 ss impala rear disc brake assembly 003

1. The complete 1996 SS Impala rear disc brake assembly put together from a wrecking yard and a local auto parts store-rotor, caliper, slider, rubber dust boots, pads, and backing plate.

gm model drum to disc brake conversion drum brake cover 004

2. We pulled off our Truespoke wire wheel and exposed the dinosaur drum brake cover hanging off our 1983 Cadillac rear axle.

gm model drum to disc brake conversion drum cover removed 005

3. Here we remove the drum cover with the old backing plate, shoes, and wheel cylinder system so that we could get to the axle shafts.

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4. We drained the oil and removed the rear differential cover so we could remove the cross shaft pin. Then we pushed the shafts from the outside in so that the C-clips that retain the axle in their permanent place could be removed. We then slid out the axle shafts.

gm model drum to disc brake conversion vacuum drum plate 007

5. Once the axles were removed we had clean access to unbolt the right and left side vacuum drum plates.

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6. We took off the four bolts holding the old drum vacuum plate and replaced them with the SS Impala plates. Fits like a glove!

gm model drum to disc brake conversion axle shaft reinstall 009

7. Once we switched out the vacuum plates, we slid back in the axle shafts. You have to hold the ring gear and bearing in their stationary place inside the rearend housing with your finger so that the axle splines don’t knock them out of place. Once the axles are back in position, place the C-clips back on both sides and then drop back the retainer pin. A new cover gasket and oil will seal back up the differential.

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8. We assembled the new pads, sliders, and rubber dust boots into the caliper so that we could mount the disc brake unit on to the back of the plate.

gm model drum to disc brake conversion disc brake unit 011

9. Shown here are the new-and-improved rear disc brakes, assembled onto what was once a drum brake Cadillac.

gm model drum to disc brake conversion wheel reinstall 012

10. After hooking up our brake lines and proportioning valve, it was time to put the wires back on and take the Cad out for a stop.