1979-1985 Buick Riviera Brake Caliper Problems and Replacement

By Core Brake Parts Tech Team — Circleville, OH warehouse

Caliper trouble on a 1979-1985 Buick Riviera usually shows up at the rear, not the front. The rear calipers on these front-drive E-body cars have the parking brake built into the caliper itself, using a screw mechanism inside the piston, and that mechanism seizes when it sits unused. Most "bad caliper" complaints on these cars trace back to that design, a torn piston boot, or old fluid, and the fix is almost always a pair of rebuilt calipers with fresh pads and hardware.

How the Brakes Work on the 1979-1985 Riviera

For 1979 the Riviera moved to front-wheel drive and joined the Oldsmobile Toronado and Cadillac Eldorado on GM's shared E-body platform. That matters when you shop for parts: many brake components are common across all three cars, and the rear calipers in particular are the same family used on the 1979-1985 Eldorado, Riviera and Toronado and the 1980-1985 Seville.

Up front, the Riviera uses conventional hydraulic disc calipers. At the rear, cars equipped with rear discs use a GM caliper with an integral parking brake. Not every Riviera left the factory with rear discs, so look behind a rear wheel before you order anything: a caliper and rotor means you have the system described here; a round drum means you need shoes and drum hardware instead.

The integral parking brake is the part owners rarely understand. GM patented the design in the early 1980s. Inside the piston sits a threaded shaft and a nut. When you set the parking brake, the cable swings a lever on the back of the caliper, which turns the nut and drives the piston outward mechanically, clamping the pads without any hydraulic pressure. A one-way clutch lets the nut turn on the shaft as the pads wear, so every time the parking brake is applied and released, the caliper takes up the slack. In other words, the parking brake is also the rear brake adjuster.

Common Caliper Problems and Their Symptoms

Brake technicians point out that the piston seal is designed to pull the piston back slightly after each stop. As a seal ages or is contaminated, it loses that flexibility, and the result is a dragging brake and fast pad wear. A punctured or improperly installed boot lets road debris and water reach the bore, which pits the piston and usually means the caliper must be rebuilt or replaced rather than just cleaned. A deteriorated rubber hose can also trap pressure and keep a piston from returning.

Why These Rear Calipers Seize

The integral parking brake is reliable when it is exercised. The trouble is that many of these cars are now weekend drivers or garage-kept collector cars, and the parking brake may go years without being set. The screw and clutch inside the piston corrode or gum up, the self-adjuster stops working, the pads drift away from the rotor, and the pedal gets longer and longer. Owners often chase that low pedal with a master cylinder or repeated bleeding, when the real issue is two rear calipers that stopped adjusting.

Old brake fluid makes it worse. Glycol-based brake fluid absorbs moisture over time, and on a car this old, the calipers have likely seen years of wet fluid sitting against the piston and the internal mechanism. Use the fluid type printed on the master cylinder cap or in the owner's manual, and flush it when you replace the calipers.

Replacing the Calipers: What the Job Involves

This is a moderate job for someone with basic tools and brake experience, but the rear calipers have two traps that catch people.

1. The piston does not push back. Because of the internal screw, the rear piston must be rotated back into its bore, not pressed straight in with a C-clamp. Forcing it can break the internal mechanism. A caliper piston tool with the right lugs, used to turn the piston while applying light pressure, is the correct approach. When the new pads go in, the notches on the piston face must line up with the tab on the back of the inner pad.
2. Cable adjustment must follow the book. Trade guidance for these calipers is that the piston should be turned fully to the bottom of its bore before the parking brake cable is adjusted, and the lever at the back of the caliper must return to its stop with the cable just taut. Too tight and the brakes drag; too loose and the lever knocks over bumps and the caliper will not self-adjust. Adjust to the procedure in the factory service manual rather than by feel.

Most owners replace the rear calipers as loaded or rebuilt units, sold in pairs. Replacement units for this application commonly come with the parking brake bracket, lever and return spring already installed, since those small parts are not generally sold separately. Keep the brake line connection clean: the rear calipers use a banjo fitting, and new sealing washers go on every time it is opened.

After installation, bleed the system, then apply and release the parking brake several times and pump the service brake to let the rear calipers adjust up. The pedal should come up high and firm. Torque caliper mounting bolts and the banjo bolt to the values in the factory service manual.

Front calipers are simpler: conventional pistons that retract with a clamp. Browse replacement units in our brake calipers collection.

What to Replace at the Same Time

• Pads, always. Pads that have been dragging or soaked in fluid are finished. For the rear, we carry the EBC Redstuff ceramic low-dust rear pad set for the 1979-1985 Riviera and the EBC Yellowstuff rear pads for the 1979-1985 Riviera, a higher-friction compound for owners who drive harder.
• Rotors, if scored or heat-damaged. A caliper that dragged for months usually leaves a glazed or blued rotor. See brake rotors.
• Rubber hoses. A collapsed hose can hold pressure on a caliper and mimic a seized piston, and original hoses on a car this age are due. See brake hoses.
• Hardware. Clips, pins and bushings are inexpensive and prevent noise and uneven wear. See brake hardware kits.
• Parking brake cables if they are rusted or do not slide freely, because a sticky cable will keep the new calipers from self-adjusting.
• Fluid. Flush the whole system with fresh fluid of the correct type.

Rebuild or Replace?

Rebuilding with a seal kit is practical on the front calipers if the bores are clean. The rear calipers are a different story: the internal screw, nut and clutch are what usually fail, and parts for that mechanism are not commonly sold on their own. For most owners, a quality rebuilt or new pair is the faster and more reliable route. Buy the rear calipers in pairs so both sides have the same piston condition and adjustment behavior.

If you are keeping a car that sits for long stretches, get into the habit of setting the parking brake every time you park it. That single habit is what keeps these rear calipers adjusted and moving.

Frequently Asked Questions

Why does my Riviera's brake pedal go almost to the floor even after bleeding?

On cars with rear discs, the most common cause is rear calipers that have stopped self-adjusting because the parking brake is rarely used or the internal screw mechanism has seized. Apply and release the parking brake several times and pump the pedal. If the pedal improves, the calipers need attention; if the levers do not move freely, the calipers need replacement.

Can I push the rear caliper piston back with a C-clamp?

No. The rear piston on these calipers screws back into its bore. Pressing it straight in can damage the internal parking brake mechanism. Use a caliper piston tool and rotate it back while applying light pressure.

Are Riviera rear calipers the same as Eldorado and Toronado?

The rear calipers are shared across the 1979-1985 Eldorado, Riviera and Toronado and the 1980-1985 Seville. Confirm your car's rear setup and match the part to your year before ordering, since GM changed designs in later generations.

Does my 1979-1985 Riviera have rear disc brakes?

Not necessarily. Look through a rear wheel: a caliper clamping a flat rotor means rear discs; a large round drum means rear drum brakes, which use shoes instead of pads.

Should I replace rear calipers one at a time?

Replace them as a pair. The other side has the same age and exposure, and mismatched calipers adjust differently, which can cause pulling and uneven parking brake hold.

Sources

1. US Patent 4,487,295 - Disc brake caliper with integral parking brake (General Motors) - threaded shaft, nut and one-way clutch design; self-adjustment for pad wear
2. Brake and Front End - Brake Caliper Diagnostics - jackscrew, nut and clutch operation; seal retraction, boot damage and hose restriction as causes of drag
3. Brake and Front End - Adjusting Parking Brakes - piston bottomed before cable adjustment; slack cable causes knocking; adjust to spec, not by feel
4. Rustic Disc Brakes - Eldorado rear caliper with parking brake - shared 1979-1985 Eldorado, Riviera, Toronado and 1980-1985 Seville application; bracket, lever and spring supplied with the caliper; banjo fitting; sold in pairs
5. Mac's Motor City Garage - Buick Adopts Front-Wheel Drive: The 1979 Riviera - 1979 Riviera moved to front-wheel drive on the E-body shared with Toronado and Eldorado