Of course, they're frequently out of round, and that'll pump fluid back to the master every time the smaller diameter squeezes those shoes. We've been told that rough handling, as in dropping a drum on its edge, can put it out over .030 in. If a drum wasn't particularly robust when new, it'll be pretty weak after it's been turned a couple of times, so just putting on the parking brake when everything's hot can make it cool down into an oval. If that drum's getting close to the limit or is badly rusted, it's just not going to be as resistant to going oval as a new one would be. Another weakening factor we've seen reach scary proportions is rusty drums with huge chunks of iron oxide falling off.
Replacement is the answer.
Inc. All Rights Reserved. From the November 2000 issue of Motor Service .