Help please 63 Monza brake issue

[Gary lot327]

I was driving my 63 Monza Convertible at the weekend probably drove for 50 miles and encountered some heavy traffic with stop start driving and heavy traffic, turned off at a junction and suddenly the rear brakes locked up solid, like the handbrake had just been pulled on(sorry from the uk so probably park brake) stuck across a junction was pretty hairy, however 5 mins cooling meant the car could just roll, pulled it to somewhere safer, tried the brake pedal and initially went to the floor, few pumps and it got better, I guess the brake fluid boiled due to the rear brake heat. Where do I look first and has anybody ever had a similar issue.

I would appreciate any assistance


Sent from my iPad using Corvair Forum mobile app

[bbodie52]

I'll offer a few guesses — but there is nothing like a thorough physical inspection to try to locate some physical indications of the cause.

Frequent start/stop driving, as indicated, may have caused a heat buildup due to frequent application and possibly dragging of the brakes. This may have caused some expansion of the rear wheel cylinder components as they heated. If there is any corrosion or pitting in a cylinder, the clearance between the piston and cylinder may have decreased with heat buildup to the point where a piston jammed or got stuck in the cylinder and the springs were unable to return the shoes to release the brakes. The brake pedal later going to the floor is another symptom of boiling brake fluid. Water buildup in aging brake fluid can lower the boiling point of brake fluid.

Rear drum brakes can lock for several reasons. One reason could be a defective wheel cylinder, which is part of the brake system. It is found on top of the shoes, and its function is to place force on the shoe so it comes into contact with the drum. A defective cylinder can cause brake lock up. Your brake cable could also be adjusted too tight. The slightest pressure on the brake pedal, will then cause the brakes to work at full force, causing the lock up. Loosen the cable a bit, in order to relieve some of the tension on the brakes, and avoid them locking up

The brake systems are normally reliable. Brake fluid is hygroscopic and absorbs moisture from the air over time. Flush and replace the fluid every few years to prevent rust and corrosion in the master and wheel cylinders and steel brake lines. A dual master cylinder was introduced in 1967, and can be retrofitted to 1962-1966 Corvairs. Rubber brake lines can swell up internally and decay with age.

If your inspection points to rust or corrosion in a wheel cylinder, all four wheel cylinders and the master cylinder may be suspect for developing problems. At a minimum you would have to repair or replace the defective cylinder, but the condition of the others may have also been affected by moisture in the brake fluid, age, and other operating conditions that are common to all four wheels.

Also be sure to check the parking brake cables and pulleys. These are particularly important on a Powerglide automatic transmission-based Corvair, since the Corvair automatic lacks a PARK position to lock the transmission. Because of that the Corvair relies heavily on the parking brake system, which is the only thing that prevents your Corvair from rolling away on a hill! If a plastic pulley cracks or a cable snaps (usually without warning) your car can decide to take an unaccompanied trip without your permission.


http://www.corvair.com/user-cgi/catalog ... N&page=143

http://www.corvair.com/user-cgi/catalog ... N&page=145

http://www.corvair.com/user-cgi/catalog ... N&page=148

[joelsplace]

It sounds like more than one problem to me. Stuck wheel cylinders or collapsed brake hoses will cause locked up brakes. "Suddenly" is a puzzler. Usually they are more gradual as they get hotter.
The master cylinder is probably another issue. It's really hard to get brake fluid to boil in a drum brake system because the fluid is not anywhere near the friction surface like it is on disk cars but as Brad mentioned it will boil at a really low temperature if it is old and water logged.