Freight Car Brake Adjustment

[Anonymous]

For a period of time many years ago I was an assistant trainmaster on a freight railroad that serviced the US Steel mills in the Pittsburgh area. I recall that every day our car department inspected about 25% of the hoppers that came through one blast furnace plant after these cars were emptied of iron ore or coke, repairing safety defects like bent sill stirrups & grab irons, etc. I also remember the car folks replacing the brake shoes on some hoppers because these shoes were worn beyond acceptable limits.

I know that these hoppers had adjustment "holes" in their brake levers & rigging so that as their brake shoes wore down from use, the brake rigging could be adjusted to compensate for this wear, allowing acceptable braking force to be maintained during the life of the brake shoes. However, I don't remember the car knockers EVER having to change or "back off" any adjustments in the brake rigging to replace a worn shoe with a new one. They seemed to always be able to simply pry the brake shoe back enough from the wheel with a short bar to pull a "key" out of the shoe holder, remove the worn shoe & then put a brand new shoe in its place.

Since it appears we never had to back off the rigging adjustment to put new & thicker shoes in place, I'm led to believe that these brakes were NEVER adjusted to compensate for shoe wear - the rigging was left in its "new shoe" position so replacement didn't require fiddling with the adjustment. This of course means that braking force varied widely in a train of hoppers, as we did not run "unit trains" like is done today.

I've recently read about "automatic slack adjusters" that adjust the brake rigging as the shoes wear to maintain relatively constant braking capability. Are these adjusters required issue on ALL new freight cars, and if so, how long have these been mandated? If not, are they mandated on certain types of cars? And have all "old" (non slack-adjusted equipped) cars of types required to have these been retrofitted?

SBradyR

[mvlandsw]

I worked as a car repairman-air brake repairman at the Union Railroad car in Pittsburgh. Sometimes I had to let out some slack to replace brake shoes. Usually this was when several shoes needed to be replaced. When I was doing air brake tests I would take up the slack to get the piston travel within the required limit. It's probably true that the brakes were rarely if ever adjusted outside the car shop, but at the time all cars were required to have their air brakes inspected and tested every 90 days. I believe that all cars now have automatic slack adjusters but I don't know about when they were required or about retrofits.

[Anonymous]

I worked in a freight car running repair shop around 1960, and all freight cars were equipped with manual slack adjusters on both ends of the car. Automatic slack adjusters were just beginning to appear. Manual slack adjusters had been in use for many years, and were used, as noted, to keep piston travel within prescribed limits.

The air braking system of a freight car was based on equalization of pressure with a maximum piston travel of six inches. Less piston travel resulted in higher braking force; more travel in less braking force. The arbitrary figure was seen as a compromise - enough to provide adquate braking for a loaded car, but not enough to slide the wheels of an empty.

Old Timer

[Anonymous]

As previously stated, slack adjusters change the length of one or more parts of the brake rigging to maintain constant brake cylinder travel as the wheels and brake shoes wear. Office Manual Rule 88 of the AAR Interchange Rules requires that New, Rebuilt and Modified cars and cars increased in gross rail load or receiving Extended Service Status must be equipped with AAR-approved automatic slack adjusters. I don't recall when automatic slack adjusters were first required on new cars, but it has been at least 30 years. Cars built prior to July of 1974 were limited to 40 years life unless Rebuilt or Granted Extended Service Status, so the number of cars without slack adjusters is dwindling fast.

[sd90macphII]

Slack adjusters are on all cars built after 1970 and most cars built after 1960 have been refitted with slack adjusters. I am a carman in a running repair shop so we do all types of air brake work. Including slack adjuster replacement. Very few cars have manual slack adjustment anymore. Those that do are not in interchange service.