Martin's question about the centerpost height
Martin -
To answer your question to John, the centerpost was shortened 5 or 6 inches in very early 1978, maybe even on 1/1/78. This involved 24-inch machines, 29-inch standard capacity, AND 29-inch large capacity models such that they all continued to use the same length spin tubes.
This change did not effect the transmission shafts or the agitators. A length change that did though happened on the large capacity +- 27 gallon models in late 1973, which also changed the centerpost height. Prior to this, these large cap. machines had their own centerpost length, their own spin tube length, and their own agitators. Kenmore had been using a large Super Roto-Swirl for several years, and WP used the S Surgilator, which as John said just had a lengthened centerpost, I don't think it was much different in lower skirt or fin area, etc. This change shortened the agitator shaft to be common with the standard capacity models, thus the same gearcases could be used in all models, and therefore all the agitators in use at the time became interchangeable.
In total, the 27-gallon large capacity machines had three centerpost and spin tube lengths during their production:
Version 1, the tallest from 1967-1973, which started with the whopper black bakelite agitators and later the big Roto-Swirl, and tall but otherwise the same Super Surgilator.
Version 2, which dimensionally matched standard capacity models from late 1973 to 1978. The centerpost, spin tube, and gearcase shaft of the large machines were all shortened to match then current production standard machines. This was when the Penta-Vane and Penta-Swirl were developed, and when WP started using the standard-looking Super Surgilator in their big capacity machines.
Version 3, in which the centerpost and spin tube was shortened 5 more inches from 1978 to summer 1981. This change was strictly "under agitator" and nobody could see this unless you pull the agitator, and no new agitators were developed due to this change. These machines are immediately obvious when the agitator is removed as much of the agitator shaft, that is covered in the older models, is now exposed.
The 27-gallon sized machine ended production in summer 1981 in favor of the 22-gallon "Energy Efficient" belt-drive. These again used the same centerposts, basket drives, and transmissions with the standard machines, and even the same baseplates this time.
Clear as mud?
Gordon