Hello,

Before we decide to hire a contractor. Is changing a AB universal packing cup in the cylinder something a mechanical person could do?

Thanks
Maria

Yes. It is not a difficult procedure at all. Care and cleanliness is essential, as is use of the proper AAR-specification brake cylinder lubricant.

Howard P.

Are you talking air brakes? Changing a packing up is not too hard to do. The older and larger sizes can get heavy. A small forklift can be a help. There is a large spring in there, so make sure there is pin through the hollow rod to retain the non pressure head until you are ready to remove it. Sometimes the return spring and cast iron mounting ring are broken You will need to deal with if it is the case. You will need the AAR approved grease to relubricate prior to reassembly. Prior to disassembly clean everything as best as you can. During reassembly it is very important to keep dirt and grit off all the relubricated surfaces. To get the piston with the new cup back in the cylinder, put the piston in at about 45 degrees. Then lift the hollow rod up to horizontal and the new cup should be in place. The whole job can be made a little easier by disconnecting a fitting in the brake cylinder pipe so you do not have to fight vacuum or pressure as you try to move the piston in the cylinder.

I agree with everything Dave J. posted.

Is this a freight car or a passenger car? What size is the brake cylinder? The size is usually stamped
on the end castings. I would expect "12" or "14" but sizes from 8 to 16 (in 2" increments) were typical.
Be aware that there are two different styles of cup. The older "WABCO" style is like a typical "PC" pneumatic packing cup, but most of the solid face of the cup has been cut away so it looks more like a flanged ring. This type of cup is held between the metal piston and a large metal follower disc, and the whole thing is bolted. The newer style I call an "umbrella" and was used on the "U" series of cylinders, e.g. UAHT. These cups have a much more complicated shape and snap into a groove in the piston.

I have always wondered what the characteristics of the AAR grease was that made it so magical for these applications.

Wabtec calls it universal 10 inch packing for AB brake cylinder. It's on old boxcar

A few details:

Changing the packing cup isn’t difficult but it can be a gooey, messy job. Cleanliness of lubricated surfaces is supreme. It can be a two-person job if you’re sitting on the ties under the car. Before you start, make sure you have a replacement gasket for the non-pressure end you’ll be removing from the cylinder. You should also replace the flange gasket on the air line to the cylinder that you’re gonna have to crack open to shove the piston in. Bleed all the air off the car before you start anything.

Wipe out the old grease. You’ll need plenty of rags/shop towels and disposable gloves. Wipe the hollow piston shaft, too since that gets greased. Coat the cylinder, and the hollow shaft with new grease. Smear a little on the cup lip. Don’t forget the new gasket or you’ll be pulling the piston back out.

Like Dave said, tilt the piston a bit to get it stared back in. This is where you may need help since you’ll need to work the rest of the cup lip into the cylinder with your fingers. Shove the piston back in wiggling it a bit since it will be a more snug fit than the old cup.

Button everything up and test for leaks.

AAR cylinder lube is both sticky and slippery and seems to get all over you no matter how careful you are. Make sure you have plenty of hand cleaner.

A scissor-lift table makes lifting the brake head + piston + cup assembly a lot easier and safer when working underneath a railroad car. Up/down is under your control using the manually-operated hydraulic pump.

For Niles Canyon Railway, I purchased a sturdy made-in-USA scissor-lift table from a local Craigslist ad. Facebook Marketplace is also a good place to look.

- Doug Debs

>The older "WABCO" style is like a typical "PC" pneumatic packing cup, but most of the solid face of the cup has been cut away so it looks more like a flanged ring. This type of cup is held between the metal piston and a large metal follower disc, and the whole thing is bolted. The newer style I call an "umbrella" and was used on the "U" series of cylinders, e.g. UAHT. These cups have a much more complicated shape and snap into a groove in the piston.

There are two varieties of the older, ring style cup: leather and rubber. Leather is very rare these days, but it requires and expander ring which forces its lip against the cylinder wall when there is no air pressure. The rubber type doesn't require this expander ring -- in fact WABCo says to remove it when converting to rubber.

Snap-on packing cups are also used in freight brake cylinders. Current recommended practice with this type of cup is not to apply grease to the dome section. This is the result of an incident about 20-25 years ago when some whiz kid in the rubber plant tried to economize on production costs by leaving an ingredient out of the rubber formula. The result was that the grease was able to cause the cup to expand to the point the piston wouldn't move. WABCo corrected the problem and fired the guy, but the recommendation about not greasing the dome part of the cup remains (as far as I know).

I’d guess the biggest thing would be the compatibility of the grease with the rubber cup formulation and visa versa. Back in the days of my real job, I had to be aware of how different types of elastomers reacted with different petroleum products and chemicals. It also needs to be able to not degrade with water.

Are you sure that's the style of cup that is actually in use. It depends how "OLD" the boxcar is. Do you have a photo of the cylinder?