1978-1979 Buick Century Brake Caliper Problems and Replacement

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 1978-1979 Buick Century uses the GM "metric" single-piston floating caliper on its front disc brakes, the same design GM fitted to its 1978 and later A-body and G-body mid-size cars. The most common problems are a sticking piston or seized slide pins, which show up as a pull to one side, a hot wheel, and one pad worn far more than the other. The fix is usually a pair of replacement calipers with new pads and fresh hardware, followed by a full fluid flush.

How the front brakes work on a 1978-1979 Century

For 1978, GM downsized its mid-size cars onto a new A-body platform, and the Century was part of it. Wilwood, which builds a bolt-on replacement for this caliper, describes its fitment as General Motors 1978-1987 A/G-body cars, 1982-1991 F-body cars and S10/S15 trucks that use the "metric" caliper. Hawk lists its HB119 pad shape as a front application for the 1978, 1979 and 1980 Buick Century, which confirms these cars share that caliper family.

The metric caliper is a floating design. There is one hydraulic piston on the inboard side only. When you press the pedal, the piston pushes the inner pad into the rotor, and the reaction slides the whole caliper body inward on two guide pins so the outer pad clamps the other face of the rotor. That sliding motion is the part that fails most often on a car this old, because the pins, bushings and sleeves sit exposed to water, road salt and decades of heat cycles.

The rear of the car uses drum brakes with wheel cylinders, so the calipers you are dealing with on a stock Century of these years are the two at the front.

Symptoms of a failing caliper

• Pulling to one side under braking. If one caliper grips harder or releases slower than the other, the car darts toward that side.
• Pulling or drag while cruising. A caliper that does not release keeps the pad on the rotor. The car may drift toward that wheel even with your foot off the pedal, and fuel economy drops.
• One wheel much hotter than the other after a short drive, often with a burning smell and heavy brake dust on that wheel only.
• Uneven pad wear. Brake and Front End, citing Cardone, lists uneven wear, one pad wearing faster than the other, as the classic sign of a slider caliper that cannot move freely. On a metric caliper, the inner pad wearing to the backing plate while the outer pad looks healthy points at seized pins or a sticking piston.
• Noise. ADVICS names brake pad noise and excessive pad wear as the main indicators of sticking slide pins.
• Fluid on the inside of the tire or wheel. A leaking piston seal or dust boot lets fluid out; that is a replace-now condition.
• A soft or sinking pedal, which can come from a leaking caliper, but also from the master cylinder or rear wheel cylinders, so check all of them.

What causes it on a car this age

Most Century calipers still on the road have either sat for long periods or been through many seasons of weather, and both are hard on a floating caliper.

Seized or binding guide pins

ADVICS explains that pins rust once the grease is gone, and that heat and friction damage the pin boots and sleeves, letting water in. Brake and Front End lists the full set of causes for a caliper that cannot slide: bent or binding mounting pins, worn slides, bent or damaged mounting brackets, swollen or hardened guide seals, and lack of lubrication.

A corroded or sticking piston

Brake fluid is hygroscopic: it pulls moisture from the air over time. That water corrodes the caliper bore and piston from the inside. If a torn dust boot also lets road water reach the outside of the piston, rust builds up where the piston meets the bore and the piston will not retract.

Old fluid and a car that sits

Water in the fluid also lowers its boiling point. The federal brake fluid standard, FMVSS 116, requires DOT 3 fluid to have a dry boiling point of at least 401 F but allows its "wet" boiling point, measured after water absorption, to fall to 284 F. A collector car that is driven rarely can sit for years with fluid that has never been changed, and the calipers pay for it.

Diagnosing it before you buy parts

1. Drive and compare. After a few miles with gentle stops, carefully feel near each front wheel hub or use an infrared thermometer on each rotor. A clearly hotter side is the dragging side.
2. Spin the wheels. With the front of the car safely on jack stands, each wheel should turn by hand with only light pad contact. A wheel that is hard to turn, or that turns freely before the pedal is pressed but not after, is dragging.
3. Pull the caliper and look. Check both pads for uneven wear, check the pins and bushings for rust and torn boots, and check the piston boot for tears or wetness.
4. Check the flexible hose. A rubber brake hose that has collapsed inside can act like a one-way valve and hold pressure on the caliper. If the caliper releases once you crack the bleeder, suspect the hose, not the caliper.
5. Look at the other side. If one caliper is bad, the other is the same age and has had the same fluid.

The fix: which parts to replace

A caliper with a leaking seal, a pitted bore or a piston that will not move goes in the replacement pile. Rebuilding with a seal kit only works if the bore is clean and smooth, and on a caliper this old it usually is not. Replace calipers in pairs across the axle so both sides clamp the same way and the car stops straight. Shop replacement brake calipers and filter to your car.

Replace these at the same time:

A note on fluid: use the grade printed on the master cylinder cap or in the owner's manual. Do not mix silicone DOT 5 fluid, which the federal standard requires to be dyed purple, with the glycol-based DOT 3 or DOT 4 fluid in a system that already contains it.

Upgrade options for a metric-caliper Century

Because the metric caliper was used across so many GM cars and in racing, there are more choices than most owners expect. Hawk makes the HB119 pad shape at 0.594 inch thick in several compounds, from the HPS 5.0 street pad to motorsports blends; Hawk notes the HPS 5.0 is designed for iron rotors, not carbon ceramic. Wilwood makes a forged aluminum D154 caliper that bolts on in the stock location over the original rotor, with stainless steel pistons, high-temperature square-face seals and zinc-plated slide pins, and it accepts Wilwood or OE-replacement-style pads. For a driver that sees normal street use, a quality stock-style caliper with good pads is all the car needs.

How hard is the job?

This is a manageable job for a home mechanic with basic tools. The metric caliper comes off by removing its two guide pin bolts, and the brake hose attaches with a banjo bolt and sealing washers. Use new copper washers, lubricate the new pins and bushings with high-temperature caliper grease, and torque the guide pins and banjo bolt to the values in the factory service manual. Then bleed the brakes starting at the wheel farthest from the master cylinder, pump the pedal to seat the pistons before driving, and bed the new pads following the pad maker's instructions. Figure on an afternoon for both front calipers, pads and a full bleed. If anything on the hydraulic side feels beyond you, this is a job for a shop; brakes are not the place to learn by trial.

Frequently Asked Questions

What calipers does a 1978-1979 Buick Century use?

The front brakes use the GM metric single-piston floating caliper, the design GM used on its 1978 and later A-body and G-body mid-size cars. Confirm the part by year and trim before ordering, since options and equipment varied.

Should I replace both front calipers or just the bad one?

Replace both. They are the same age, have seen the same fluid, and a new caliper on one side and an old one on the other can make the car pull.

Why is only my inner brake pad worn out?

On a floating caliper, the piston pushes the inner pad directly, and the outer pad only works if the caliper can slide. An inner pad worn far more than the outer one usually means seized guide pins or a sticking piston.

Can I just rebuild my original calipers?

Only if the bore and piston are clean and free of pitting. Rust in the bore will tear a new seal quickly. Most owners replace them because it is faster and more reliable.

What brake fluid should I use?

Use the grade on the master cylinder cap or in the owner's manual. Do not mix silicone DOT 5 with glycol fluids. Whatever grade you use, flush it regularly, because glycol fluid absorbs water and its boiling point falls as it does.

Do these pads fit the Century rear brakes?

No. The Century of these years uses drum brakes at the rear, so the rear needs brake shoes, not pads. See brake shoes.

Sources

1. Hawk Performance - HPS 5.0 HB119B.594 - front fitment for 1978-1980 Buick Century, 0.594 in thickness, iron-rotor use
2. Wilwood - Forged Billet GM Metric D154 Caliper flyer - metric caliper fitment on 1978-1987 A/G-body cars, upgrade caliper features
3. ADVICS - Troubleshooting Caliper Slide Pin Sticking - symptoms, causes and fixes for sticking slide pins
4. Brake and Front End - Bent or Binding Mounting Pins (Cardone tech tip) - uneven pad wear, causes of binding, replace hardware and use caliper lubricant
5. 49 CFR 571.116 (FMVSS 116) - Motor vehicle brake fluids - DOT 3 dry and wet boiling points, DOT 5 purple color