Adler's Antique Autos, Inc.
Author of "Notes from the Corrosion Lab"
801 NY Route 43, Stephentown, NY 12168
(518) 733 - 5749 Email
by Bob Adler
There are lots of reasons for tight drums: broken return spring, shoes adjusted too tight, rust between shoes and drums, rust in pistons prevent shoes from retracting, rust behind linings pushing them off shoes, previous mechanic didn't understand or address principles of mechanics, hydraulics, or corrosion. Let's also assume the adjusting screws are frozen or do not loosen the drum. The first step is to get the wheel to turn.
Loosening the bleeder screw or inlet pipe can back off seized shoes if hydraulic pressure is holding the shoes tight. If this doesn't work, and the wheel absolutely will not turn, a “torque arm” wheel can be made up by welding a six foot channel iron to the inner flange of a spare wheel. This wheel then bolts on backwards using all lug nuts. Alternate a 10 lb. hammer and floor jack applied to this torque arm to break the drum loose from shoe. Once the wheel will turn, replace the wheel and tire assembly, and tow the vehicle on the road. In short order the friction wears down the lining, rubs off rust, and heats the drum to expand it. While hot, the drum may pry off easily. If not, it may be possible to unscrew the wheel cylinder and knock it off the backing plate, allowing the shoes to retract. This step has never worked for me! The ultimate drum remover is a large gear puller. By tightening this carefully, the drum can usually be saved without distortion. Remember, hammering directly on the cast iron can easily crack the drum, so keep hammer blows very light. The large gear puller turned out to be an excellent investment as I've saved many drums and backing plates that would otherwise have been bent or cracked and unusable.PROPHYLAXIS
Some suggestions to prevent brake disasters: Keep bleeder screws lubed with anti-seize compound. Use stainless steel bleeder screws. Lube all brake shoe pivots, adjusters and emergency brake inner cable with anti-seize compound. Remember, with Huck type brakes (1936-50 car and truck) the wheel cylinder dust shield is part of the adjusting mechanism—lube it liberally so it will not rust to the outside of the wheel cylinder casting. Silicone brake fluid may be beneficial to prevent internal corrosion, but it also has drawbacks.REBUILD OR REPLACE?
Back in 1937 the Chevrolet Service News (Oct. 1937 p. 70) warned that honing produces a rough surface which wears out the rubber cups much faster than the smoother factory finish on a new cylinder. Shop manuals of the past decade recommend dressing a worn cylinder with nothing coarser than crocus cloth. This cannot remove the heavy pitting usually found in the cylinders we deal with. Another precaution is replacing the aluminum wheel cylinder pistons. These are anodized at the factory. If old ones are reused, the adnodizing is generally lost during cleanup which then permits rapid corrosion. Since all hydraulic wheel cylinders, with the exception of 1949-50 cars, are readily available, I'm tending to replace more and rebuild fewer.
* Originally published in the Vintage Chevrolet Club of America, Inc.'s "Generator & Distributor", July 1990, v29, no. 7, p11.
Bob Adler is owner of Adler's Antique