The A series, along with most Wabcos, are very robust horns. They consist of a single bell with built-in nozzle, diaphragm disk, and mounting foot/back cap. On the A-2 and A-6, the bell and back cap are cast iron, and the diaphragm is stainless steel with a riveted weight in the center of the disk. The A-1 differs in that the bell's nozzle and diaphragm housing portion are bronze, and the bell is brass. On all A horns, the back cap attaches to the bell either six through bolts (A-6) or six screws (A-1 and A-2). The A-1 and A-2 are unique among horns in that they have a non-standard, square mounting foot.

There isn't much work that usually needs to be done on the A series Wabcos. Ensure that the nozzle surface is flat and without any divots, and that the diaphragm isn't cracked, and then piece the horn back together again. To assemble, place the diaphragm into the housing/bell, with the large side of the weight pointed at the bell. Next, place the small rubber gasket around the orifice so that there will be a seal when assembled. Finally, place the back cap over the diaphragm housing and attach the six screws/bolts.

B series

B-7 horns are similar to the E-44 in that they have a single or dual diaphragm disk and screw-on back cap. Also, the mounting foot is integral with the bell, nozzle, and diaphragm housing. The horns are constructed from aluminum, except for the stainless nozzle. B-6 horns are basically of the same construction as A-6 horns.

When working with a B-7 horn, check the diaphragms and put the side with least wear against the nozzle. Like all other horns, the nozzle must be flat and free from divots and other problems. Finally, the horn must be voiced. Tighten the back cap to just hand-tight. Next, with air blowing through the horn (about 20-30 pounds below operating pressure), tighten the back cap until the desired pitch is reached. Lock the back cap into place using the tooth which locks into one of the grooves in the back cap. Finally, test the horn at full pressure, and make any adjustments necessary.

D series

D series horns are basically the same as many truck horns. They contain a small, single diaphragm disk, and the back cap bolts in place with just four bolts. All the same problems to watch out for with the A series are present on the D series. However, there is one unique feature of the D series. There is a spring-loaded tensioner on the diaphragm, which adjusts with an allen wrench, and locks with a locknut. The maximum working pressure of a D-5 is 110 psi, and to operate safely at this pressure, the tensioner should be on a tighter setting. On pressures lower, such as 40 or 50 pounds, the tensioner can be loosened significantly.

E series

Finally, we come to the E series of horns. First, the E-44 is basically of the same general construction as a B-7 horn, and so the same techniques for working on these horns apply. But, I am not familiar with the E-24 bell, as I have never seen one, or even a catalog page for one. Last, the E-2, one of the oldest Wabcos, does have a few features that separate it from the other E horns. First, the earlier E-2s were cast iron, and so the diaphragm housing has an integral nozzle. The later E-2s are aluminum, but have a separate stainless steel nozzle, so as to not wear away at the soft aluminum metal.

The other main difference is the diaphragm assembly. On an E-2, the diaphragm consists of fourteen individual parts, including three main diaphragm disks, as well as six smaller disks which combine to create the clapper. I would strongly urge that if you have a working diaphragm set on an E-2 that you just leave the entire set together. There is no need to take the diaphragm assembly apart, unless there is significant wear on the top clapper disk, in which case another disk can be made the first, and the first the last. The three large leaves are not as interchangeable, though. In fact, the order they are assembled in is the only order which they will work in, as they are each cut slightly differently. Once the parts are as you want them, assemble the horn and voice it, following the same instructions given for the B-7 series horns.