The two GS-5 locomotives were actually the last two engines of the GS-4 order, but because of their roller bearing journals, they were designated as Class GS-5.* They were identical in design and construction to the GS-4 except for being a little heavier.* The GS-5 units were 110 feet 2.25 inches long and weighted 882,800 pounds fully loaded.
Why roller bearings on only these two engines?* As the story goes, the president of Southern Pacific Railroad wanted two of the new GS-4's being built equipped with Timken and SKF roller bearings to see how they work out.* Both GS-5's were equipped with roller bearings on all of the journals of the engine and tender.* Number 4458 was fitted with Timken roller bearings while number 4459 had SKF roller bearings.* It was only because of this difference that they were classified as GS-5, and they were the only steam engines built for the SP that had roller bearings (Technically, number 4459 was classed GS-5A while number 4458 was classed GS-5).* Number 4458 was set up on June 21, 1942, while number 4459 was set up on June 5, 1942.
The pictures above show roller bearings installed on trailer truck axels. On the left (top) Timken roller bearings for 4458, and on the right (bottom) SKF roller bearings for 4459.
As a side note, Southern Pacific was very cautious when considering the application of roller bearings to railroad equipment.* Each roller bearing on the GS-5 cost $27,000 more than the standard journal bearings with “spring pad lubricators” (an SP invention) used on the locomotives and other passenger equipment.* Cost was a big factor at the time and SP did not use roller bearings on any other equipment until the late 1940s when cost started to come down.* Because roller bearings had less friction, engine crews noted that it took a little more air to bring a GS-5 to a stop as they “just wanted to keep on rolling.”* Roundhouse crews knew they “really had to tie 'em down, or they'd just start rolling away.”
The GS-5's were Southern Pacific's finest contribution to motive power in the annals of railroad history.* Engine crews said they had the best ride of all the Daylight locomotives.* None were finer!
(From:
http://spdaylight.net/Engines.html)
.....already?......wow! Time's-a-flyin'.....he he! 
