Why C2 and C3 disc brakes always leak — sooner than later? Replacing Brake Calipers on a 1975 Corvette – D. Steidinger

Important: Brake work is safety critical so do it carefully and correctly, or have someone who can do it properly and carefully.

For safety’s sake, do not operate a car with imperfect brakes.

After helping fellow club member Jim Atkins with a power brake booster replacement, I looked carefully at the inside of the wheels and the calipers for signs of brake fluid leakage – because caliper leakage is an almost universal problem with 1965-1982 Corvette disc brakes.
From my inspection of Jim’s calipers, and wheels, which were dry as dust at the time we replaced the booster, I figured there was a good chance that his calipers had been replaced with stainless-steel sleeved calipers which go a long way to preventing caliper leaks.
But, several weeks later, Jim contacted me, said his brakes became weak, the brake warning lamp came on, the rear compartment of his master cylinder reservoir was near-empty and the front reservoir was halfway to empty.
My immediate worry was that the new brake booster we installed might have failed and started sucking brake fluid into the from the master cylinder into the booster. I sure did not want to go through that difficult booster replacement again.
So when I arrived back at his garage, I checked the vacuum hose to the booster, it was holding vacuum and it was dry inside – no brake fluid. I separated the master cylinder from the booster, and the back of the master cylinder was dry – no brake fluid leak there.
I started looking inside each wheel. Front and rear wheels on the left side were dry.
But the inside of the right rear wheel was wet with brake fluid. And fluid had drooled down the tire onto the floor.
I jacked up the right rear, removed the wheel and found a dripping wet caliper.
So Jim and I agreed to get fresh rebuilt stainless-steel sleeved brake calipers for all four wheels.
Why did I insist on stainless-steel sleeved calipers? It’s a long story, as in from 1965 to 1982. Chevrolet used the same design four-piston calipers. Rugged and effective – until they leak! The pistons slide in the cast-iron bores of the calipers. Those cast-iron bores get rusty and pitted when water is absorbed into the brake fluid in normal use, which makes the fluid mildly corrosive. And apparently the seals, or boots, that were supposed to keep water out of the calipers, uh, did not. How could Chevrolet have used this same trouble-prone design for 17 YEARS? A trouble-prone design that can lead to brake failure in a relatively few years? I do not know.
Dave McLellan’s book, Corvette From The Inside, a good read by the way, talks a little about this “endemic” problem. McLellan was chief engineer on the Corvette from 1975 to 1992. He writes that factory durability testing of the Corvette braking system did not reveal this corrosion/leakage problem. He essentially blames Corvette owners for not using their high-performance brakes hard enough to drive out moisture, and then letting their cars sit idle for months which lets corrosion work its damage over time. He claimed that the problem was due to the outer boot/seal that had a steel outer ring that presses into the caliper bore. The boot is supposed to keep water out, but the steel-on-cast-iron boot interface allowed water in. He claims that in later years the problem was solved by a revised boot that encapsulated the metal outside ring with ‘rubber’. That probably helped, but stainless sleeves are a better remedy – though I have seen them eventually leak, too, on relatively rare occasions.
McLellan calls the aftermarket stainless sleeving a “cottage industry”. Well, I guess his viewpoint from working for GM, any other industry is a “cottage industry”. There used to be a “cottage industry” in Florida, Vette Brakes, that was a relatively early source of these much improved, sleeved calipers. As I recall, the sleeving idea came from a Florida aircraft charter company, Chalk’s, whose fleet included amphibious aircraft. These planes could land and take off from water, ocean salt water. Their landing gear was, as a result, repeatedly submerged in salt water. And you can imagine the corrosion that salt-water submersion would cause – maybe sort of like Detroit’s six-months-long winter’s salt-spray roads?? Chalk’s maintenance crew found a way to bore out brake calipers and shrink-in a thin stainless-steel sleeve in each piston bore. Several stainless-steel alloys are highly resistant to salt-water corrosion. And someone made the connection to try this technique to solve Corvette C2/C3 disc brake failures caused by corrosion.
I think Vette Brakes has closed, but you can get stainless sleeved calipers from Corvette parts suppliers like Zip Products. I’m not sure if auto supply chain stores offer stainless-lined calipers.
The stainless-steel sleeving is a significant improvement over stock calipers, but occasionally, even sleeved calipers have leaked. The “cottage industries” attacked this problem, too. For infrequently driven cars, they suggest O-ring piston seals instead of the original lip-type seals. Personally, I’m not sure how O-rings can seal brake system pressures of 1000 psi or more, so I’ve never tried these. Supposedly, if you stay with lip-type seals, you should get into your car every month and ‘exercise’ the brake pedal a few times to keep the lip-type seal lubricated with brake fluid and sealing properly.
So, on Jim’s car, we installed and bled the stainless-sleeved rear calipers, then moved to the front.
Brake rotors were cleaned with BrāKleen® spray solvent to remove any oily/greasy brake fluid residue.
The right front caliper was leaking slightly, too. The left front looked almost new, but we replaced it, anyway. I couldn’t loosen the left front brake line flare nut, even with a proper flare-nut wrench (which, btw, you definitely need flare-nut wrenches for typical brake system work), but I could readily access the other end of that brake line at a brass junction block. We installed a new, pre-bent, shielded brake pipe and new brake hoses. We turned the front wheels full left and full right to make sure the brake lines had proper slack and did not get pinched by any nearby suspension or steering components.
All brake pads were replaced. Never re-use any brake pad that has been soaked with brake fluid. Install the new pads in the calipers, squeeze them outwards to retract them, and they will fit over the brake rotors fairly easily. Caliper mounting bolts are high strength grade-8 (with six radial marking lines on the head) and tightened to 70 ft-lbs.
Always use fresh brake fluid in the brake system — and use lots of care to avoid getting brake fluid on painted surfaces – brake fluid can remove paint. Cover fenders, have rags or paper towels at hand. Have a spray bottle with water on hand to quickly wash brake fluid off of painted surfaces. Brake fluid is water soluble and washes off easily.
Air needs to be carefully ‘bled’ out of the brake lines and calipers. This is not that hard to do, but you should have someone show you how to do this if you don’t know how. Bleeder fittings are somewhat delicate, so use a six-point socket for initial loosening and final tightening to prevent rounding off the hexagonal fitting. The bleeder will need to be tight to prevent leakage, but too tight and you can twist it off! Again, it’s really helpful to work with someone who has proper experience to show you these tools and techniques for your first time.
Brakes are critical, life-safety systems and no hacks or short cuts are allowed. No leaks are allowed.
With new brake components, make initial test drives carefully. Use the brakes gently the first 300 miles or so for the brake pads to wear into full contact with the rotors. Initial brake performance will be reduced until the pads have worn in properly.
With proper maintenance, upgrades, and break-in, C2/C3 Corvette disc brakes can be powerful and dependable.