How to Swap GM Rear Brakes to Discs

Foot to the floor for 100 feet when you brake for that bus full of nuns? Upgrade when we show you that putting disc brakes on the rear of a GM car is actually very easy. Watch as we swap out the drums on our '86 Caprice and swap in a set of discs from a '94 Caprice police car. The good news is that these tricks will work for any GM C-clip-style 10- or 12-bolt axle on nearly every GM car.

Pull the rear cover, drain the fluid, and remove the C-clips and axles. Unbolt the drum brake backing plates. You don't even need to remove the brake shoes and hardware. All you need to do is unbolt the hydraulic line going into the wheel cylinder.

Remove the drums. Replace them with the disc brake backing plates.

Replace your axles, bolt on your calipers, bleed the system, and you're good to go.

Reality Check
You're probably thinking, "That was too easy," and you're right. Yes, mechanically, the job is simple. You can swap drums for discs in a couple of hours as long as you do your research ahead of time. However, a lot of things can go wrong if you don't.

No big deal, we can just swap the axles, right? Wrong....

...The '94 axles measure 1.30 inches and have 30 splines instead of the 27-spline 1.125-inch axles from the '86.

What if we swap out differentials? Sorry, that won't work either....

The axlehousing dimensions are the same on all '77-'96 Chevrolet B-bodies (Chevrolet Caprice and impala) are nearly identical under their sheetmetal, and virtually all parts are interchangeable among those model years. We can swap the whole thing into our '86 Caprice, and in doing so, we'll be upgrading from our puny 7.5-inch 10-bolt to a much stronger 8.5- inch unit with limited slip. The rear discs are just a bonus.

...The '94 has an 8.5-inch ring gear that won't fit into our 7.5-inch '86 carrier.

...There's no way this rotor will fit. The rotors from the '94 Caprice are drilled for a 5x5-inch bolt circle. The axles in the '86 fit GM's more common 5x4 3/4-inch bolt circle.

Truthfully, we planned to swap axle assemblies all along. The point of the exercise at the beginning of the article was to demonstrate how quickly you could get mired down in the multitude of variables involved in a rear disc brake swap.

Have you ever wondered why there are so many aftermarket companies offering brake upgrade kits? Or why most car builders or restorers, guys who have no fear of building engines and transmissions, will run aftermarket braking systems on their cars? Well, neither did we until we started researching for this article. We quickly discovered that trying to cobble together a brake system involves a lot of trial-fitting until you get the combination right. Fine if you've got the time and funds.