Re the PRR Q-2, the RME 1946 January article as reprinted in Train Shed Cyclopedia (TSC) #49 confirms that it had LMDs on all five driving axles. Additionally, the #3 drivers were blind. The allowed lateral motions, from 1st to 5th driver sets, were 2¼”, ½”, ½”, 13/8”, ½”. Total wheelbase was quoted as 26’4½”, and rigid wheelbase as 20’4”. I’d guess that the rigid part excluded the 1st set of drivers. One may see that the 3rd set would need more freedom than the ½” lateral allowed, hence the use of blind tyres. Possibly flange thickness varied amongst the drivers, as well.
The Q-2 is the only example that I have found that had LMDs on all of the driving axles. It is also the only example that combined an LMD and blind tyres on the same axle. One has the impression that the PRR wanted to avoid any lateral shocks and binding, perhaps not just to ensure good tracking and riding, but also to avoid events that might incite slipping.
Pneudyne wrote:Lateral motion devices were sometimes also used on the leading axle of four-wheel trailing trucks, I think those of the traditional longer wheelbase design with smaller diameter wheels on the front axles. The short-wheelbase type with equal wheel diameters probably would not have needed them.
Not so. The short (54-inch) wheelbase trailing truck of the B&O 2-8-8-4 had a Timken LMD on its leading axle. It had Alco LMDs on its 1st and 5th driver sets. (That from RME 1944 June via TSC #47).
Re the modern branch line locomotive case, apparently CN did map out a couple of such designs, one 2-6-2 and one 2-8-2, although none were built.. Whether enough information has survived to determine whether either – but particularly the 2-8-2 - used an LMD and/or blind tyres I do not know. The C&O reverted to a pre-WWI 2-6-6-2 design for its final (1949) batch of coal branch locomotives. It did undertake some modernization, though, in that these used a latter-day single-plane, single-pivot articulation joint in place of the traditional two-plane type. That was gleaned from observation of the example at the Baltimore museum a long time ago. I didn’t notice whether it used LMDs, but with a short-wheelbase six-coupled driver set, neither that nor blind tyres were likely to have been needed.
Whether anyone would have contemplated a light 2-10-0 for branchline service in the late steam era is a moot point, but the CN example suggests that trailing trucks might have been preferred to make for easier backing-up. But in the case that a light 2-10-0 was considered to be desirable, then fitting the rearmost driving axle with an LMD and allowing a reasonable lateral excursion, say 2 inches or so, could be beneficial from the viewpoint of backup moves.