Railway Preservation News

Early Central Pacific Tender Trucks
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Author:  Train Detainer [ Thu Mar 31, 2016 3:50 pm ]
Post subject:  Re: Early Central Pacific Tender Trucks

Mr. Travis -

I didn't mean to step on anything regarding the focus on the IID trucks, but given the vast amount of different designs for these type of trucks (and everything else) back when everyone was trying to one-up each other with often unproven and sometimes foolhardy designs when RRs were front-line technology, I was trying to keep the focus on what was in front of us at the moment. I have long been interested in that era and would be very interested to see any other truck designs or information from it.

That said - and I don't mean to harp, but sometimes it's necessary - good (and necessary) practice when dealing with technical issues dictates a need for proper identification of the item(s) in question. I don't know your background and don't want to offend, but I will provide a bit of info for any who are interested and may not be aware.

On the RR we refer to things on rolling stock by their location. Usually A-end truck vs. B-end truck (or front and rear), axles numbered from B-end (handbrake end) to A-end and for wheels and other things, left and right relative to the carbody, etc.. While it might not be readily apparent to most people, there are differences in just about everything on railroad equipment depending on location and service, so discussing technical issues without thought to or accurate communication of the location and/or function inevitably leads to confusion. This is a problem even among some career RRers, so it's nothing unheard of. I've seen cars sent to the car shop with nothing on the tag but 'Bad wheel' or 'door hard to operate'. Is the wheel R2, L3 or R5? Flat spot, cracked or something else? The right side door or left side? Engine reports are sometimes sent in with only 'Low Oil' written in the comments. Lube oil, governor oil, journal oil or compressor oil? Crews will sometimes call the dispatcher with the message 'We're on the ground'. Is that one wheel, one truck, a car on it's side or is half the train all over the farm blocking the RR for days? So how do I know whether to send a block truck with a rerailer or call the fire department and the hook? Clarity, please. Anyway, I think that conveys the idea.

As for IID 151's front truck bearing, I based the flat center-bearing notion on what's visible in the pictures on the first page. The beam doesn't appear to have the long tapered neck of the rear truck's ball casting, although a ball could be worn enough that it's no longer apparent. I would assume that something this specific from the same designer would use a similar shape if the same design were used for a similar application. People tend to stick with what they know or are currently using. Again, we need first hand information to clear that up. As for the rear truck's ball and socket carrying a load, why would it? If it did, it would make the springs irrelevant given their heavy load capacity, since a load carrying center bearing for that truck would reduce the spring groups to simple side bearings with all of the tender weight being carried unsprung from the tender frame directly to the truck frame/journals/wheels on level track. The suspension would be effectively reduced to a very rigid two-point and be very rough-riding with resultant damage to both track and tender. It would also be derailment-prone, which would most likely have resulted in the design being removed/banned very quickly, so I don't think that would be correct. Your statement in you first post on page 1 was correct about no load on the center bearing - but for the rear truck only in a three-point. Also FWIW, after a closer look, my drawing of the truck bolster/side frame connections is wrong - the bolster arch bars pass completely through the side frames and bolt top and bottom between the columns and side arch bars.

As such, I have no problem with the design theory for this truck as I stated it earlier. It seems fairly straight-forward to me. If the components are as I drew them (or similar) they would provide adequate flexibility, ride quality and function for what they were intended. If these front truck spring groups functioned as non-contact side bearings as I reasoned, this design might be considered an evolutionary step between plain three-points, four-points and more modern two-points with side bearings. The design performed reasonably enough for the period it was used and was functional enough that it has lasted this long under IID151 and predecessors. It is, in my opinion, an overly complicated design that eventually failed due to load limitations, lubrication problems, better/newer designs available and probably poor ride quality at higher speeds, combined with steadily improving track conditions that rendered true three-point suspensions unnecessary.

Looks to me like Mr. Morris' miniature truck recreates the 151 front truck side frame casting pretty closely, particularly with regards to the beam/spring link guide. I myself have been working on a pair of USMRR trucks for a 1/8 scale tender and learned a great deal about their construction from doing so. I have no original drawings and took everything from photos.

Off of IID151, Mr. Marshall has provided us with a nice pic of an even nicer Woodstock #3, which, from this one picture taken at a very good angle, appears to have a four-point suspension tender similar to CP229's with another variation of spring suspension at the frame (longitudinal swing links at the spring clamps?). Would be very interesting to see what's between the bolster centers. Two things in this pic really pique my interest - the rail profile of the foreground tracks and the rear tender axle seems to be derailed with the rim slightly below the rail head. The front half of the spring group above the derailed axle seems to be relatively straight and under heavy load while the rear half is curved down as if unloaded. That said, the rim of the rear wheel is still partly visible above the rail, so is this an indication of a very limited truck motion or is the flange sitting on the table latch?

Author:  Ron Travis [ Fri Apr 01, 2016 8:24 pm ]
Post subject:  Re: Early Central Pacific Tender Trucks

Train Detainer,

As I mentioned, I have been interested in these trucks with the big elliptical, springs providing direct side bearing suspension. I assumed that they carried the weight directly from the side sills of the tender frame directly onto the tops of the journal boxes. I also reasoned that they could not have a conventional load bearing center bearing as that would conflict with the outboard load path as described above.

However, other than a confirmation from Ron Goldfeder about the telescoping center bearings of C&NW #274, (which he mentioned on page 2), I have almost no information about the details of the center bearings used in general with trucks having the characteristic outward appearance of this general category.

So, in consideration of this experience, I did not have any expectation of seeing the details shown in the photos of the trucks under the tender of IID #151. So I will describe what I find somewhat puzzling about what I see and don’t see, and about the apparent design principles.


It appears to have a telescoping connection between a round pin standing vertically atop the truck bolster and fixed to it; and a round bore made vertically through an expanded portion of the equalizer lever. This would provide a slip fit for the telescoping connection. The photos do not show the relative diameters of the pin and the bore.

Since the equalizer lever must tilt relative to the nominally horizontal plane of the truck bolster, the tilt would cause the axes of the pin and the bore to become non-parallel. Therefore there must be clearance between the round pin O.D. and the I.D. of the bore though the lever in order to prevent interference from relative tilting which would bind the telescoping action.

Given the amount of potential tilting, I speculate that there must be a gap of at least ½” all around the telescoping action between the pin and the bore.

The loading on this connection would be only radially in the nominally horizontal plane; if the pin and bore happened to move horizontally relative to each other, and closed up the ½” clearance gap. If the axes of the pin and bore happened to be parallel at that moment, the loading would be a straight, vertical line along the contact between the pin and the bore. However, if the axes of the pin and bore happened to be non-parallel at that moment, the loading would be a single point where one of the two ends of the bore contacts the side of the pin.

Therefore, as a true radial bearing, this connection would be quite a compromise with its contact randomly focused on lines and points, and being momentary with potential impact. Furthermore, the pin and bore will be sporadically moving vertically relative to each other as these radial contacts provide relatively high impact loads on very small areas. So as these impact contacts occur, the contacting surfaces may also be subjected to a high pressure rubbing action. Not only would this produce wear, but it might also bind and seize the telescoping action, and possibly derail the truck.

It seems that the proper way to regard this telescoping bearing would be as a safety connection or backup in case the truck moved too far horizontally in relation to the tender. The larger the gap between the pin and the bore; the less the wear and tear, and potential for binding; but the greater the risk of too much misalignment between the truck and the tender horizontally.

The height of the vertical bore appears to be about 5-6”. If the height of the bore were reduced, the clearance gap could also be reduced while still giving enough clearance to accommodate the misalignment of the axes of the pin and the bore. But then this might wear the bore larger more quickly because the surface receiving contact between the pin and bore would be of less total area subjected to the contact forces more often. Although there would be less potential for impact associated with those forces.

If there is a conventional bowl and boss center bearing transferring weight directly from the tender frame center to the top of the equalizer lever, I assume that it also has a conventional center pin. Perhaps it is the same center pin that we see entering the bottom of the equalizer lever.

Like the telescoping pin/bore radial bearing, the bowl/boss center bearing will have to accommodate variations in the axes of the boss and bowl. Although, this factor may not be unusual compared to current practice where the same misalignment of axes occurs due to the rocking of the car and the tilting of the truck bolster.

However, in the case of this truck, perching the boss/bowl atop the equalizing lever seems unstable compared to current practice where the center bearing sits atop a the bolster having a base wider than its height, and with the wide base sitting atop a nest of compression springs on each side. The bolster is further stabilized by the ride control wedges, and in some cases, constant contact side bearings.

All of this makes the bolster of current practice much less able to tip fore and aft under the weight of the center bearing than would be the case with this early truck with the center bearing loading down onto a relatively narrow standing blade (the equalizer lever) supported only by a small pad on each end measuring only about 3-4” longitudinally. It appears that the point of the center bearing on top of that blade would be about 6-8” above the 3” wide support pads. It seems that this would tend to tip the equalizer lever over fore and aft as the tender bounces up and down and tends to disengage the bowl and boss of the center bearing. Although the spring hangers would also contribute some anti-tip reinforcement to the equalizer lever.


In consideration of the apparent shortcomings of the front truck center bearing principles, I am surprised that the designer would have opted for a center bearing for the rear truck with such sophistication as a ball/socket joint.

And if that ball joint does indeed telescope, as would seem necessary, I am surprised to see what appears to be a hemispherical relationship between the bottom of the ball and the bottom of the socket. Why go to the trouble of matching two hemispheres that never contact each other?

If it is a telescoping ball joint, the benefit is obvious. It can telescope just like the front truck, but the ball joint permits the tilting of the bolster relative to the horizontal plane without the need for the excess clearance that is needed between the pin and the bore of the front truck. With the closer fit of the ball joint, it can be more proactive in controlling the pivot center of the truck; as opposed to just acting as a safety catcher which only occasionally sees a load. And the more constant loading of the ball joint with its closer fit will reduce the impact loading that may occur with the greater clearance of the pin and bore of the front truck center.

Perhaps the ball joint does not have the ball itself telescoping in a bore. Maybe, instead, the ball has its center point fixed by the containment of the socket top and bottom; and the telescoping occurs as a round pin passes through a cylindrical bore through the center of the ball vertically. The telescoping pin would accommodate the vertical movement while the rotation of the ball joint would accommodate the tilting of the bolster.

Author:  Dave [ Fri Apr 01, 2016 9:32 pm ]
Post subject:  Re: Early Central Pacific Tender Trucks

Somebody had a set of drawings we only saw a part of, and it wasn't all that clear, still......

if there is a center telescoping shaft between the center of the truck bolster and the car bolster with a interface between the two, who's to say there's not a spring inside the telescoping section surrounding the center pin to provide a certain amount of compression to assure they stay where they are supposed to be?

Author:  Overmod [ Sat Apr 02, 2016 9:41 am ]
Post subject:  Re: Early Central Pacific Tender Trucks

If you think about it a moment, there's no need for any 'spring' inside the telescoping connection; it's there to accommodate the vertical compliance of the very capable side-bearing springs, and they do the job quite well. The center post has to 'telescope' because it is the only thing that keeps the truck centered and pivoting, and I personally suspect because an 'unprotected' kingpin of the necessary length with only a bolster bearing would have 'tribological difficulties'.

I am satisfied that the arrangement of the 'horizontal equalizer' is to permit the load on the 'ring' around the kingpin to be transferred from the center of the tender front down to the two spring perches (and thence to the journal boxes). The rigid H-frame is probably to keep the plain bearings for the axles aligned so the bearings and journals have a reasonable life. Note the bolts that may act as stops for truck swing -- do we know what those actually 'do' in this design?

Something that bothers me, and I don't have a really good explanation for, is the arrangements at the top of the spring perches for that rear truck - the one with defined contact with the tender side-sills for the 'three-point suspension'. I don't see arrangements in the pictures that indicate this truck has very great pivot swing under those little blocks (compare the situation with the arc necessary for three-piece truck CCSBs at a somewhat smaller radius). That indicates to me that the truck may be intended not to swivel very far, designed as if it were a wagon with a steering axle and relatively 'fixed' rear axle towed from the front, but with the springs as far outboard as possible for stability. Here the ball-and-socket joint just needs to accommodate the rocking (fore-and-aft, side-to-side, or some resultant) of the H-frame relative to the tender sills, and if I am right its vertical location is an expected geometric center of this movement relative to the spring system that 'cushions' it.

We know, from John White for example, that the 'early' designs of these side-bearing trucks could be 'hard on the springs', and that early versions that did not constrain spring-perch angle 'horizontally' -- for example the very lightweight trucks originally installed on NYC 999 -- rapidly acquired rather substantial 'plates' to control some aspect of thers deflection when running. I would be specifically interested to determine what the plates in these various Central Pacific truck designs actually do, and what their points of contact with the spring structure are intended to be as the truck swings.

Author:  Train Detainer [ Wed Apr 06, 2016 11:34 pm ]
Post subject:  Re: Early Central Pacific Tender Trucks

Based on Mr. Morris's dimensions and a little guestimation, I've updated the previous drawing to scale and added some detail. Shown here with 33" wheels at 44 1/4" centers at the tender centerline and the side sill. There is not enough shown in the pics to see the body bolster design beyond a twin plate similar to the side sills, so I left it as a simple beam for now. I took the rear truck pinned wedge from the CP229 drawing and added a grooved bearing plate simply on conjecture and for the front truck I added an actual center pin and stepped bore in the transverse beam. One point of design economy I came across - it appears the three centre columns in each arch bar assembly may be the same casting.
Center.Side.jpg [ 125.32 KiB | Viewed 2017 times ]

Perhaps the ball joint does not have the ball itself telescoping in a bore. Maybe, instead, the ball has its center point fixed by the containment of the socket top and bottom; and the telescoping occurs as a round pin passes through a cylindrical bore through the center of the ball vertically. The telescoping pin would accommodate the vertical movement while the rotation of the ball joint would accommodate the tilting of the bolster.

It could be, but I don't see it in the pics. The socket appears to me to have more or less vertical sides above a bottom hemisphere like I drew it above, and I still think that's a rubber covered ball or lined socket to reduce wear and impacts. If it were a captured/bored ball, the socket would likely be more closed at the top for capture and there would be no need for a rubber cushion if the ball were fixed in location for all three axis. I'd really like to take this tender apart and see it for what it is.

To give an idea of what the truck would do when skewed I put this together. Beam and spring groups are rolled 1 degree and the truck frame rolled another degree.
flexed.jpg [ 137.48 KiB | Viewed 2017 times ]

The larger bore in the beam is shown as 5/16" larger than the truck post and gives plenty of room to augment flex between beam and truck bolster. I don't believe this is necessary or desirable, but I included it to show what would result between beam and truck bolster laterally (but with no additional spring compression shown). If this loose fit was original condition, any wear would allow the beam ends to contact the side frame during severe impact/heavy spring compression under truck roll conditions. It would also contribute to Mr. Travis' 'narrow blade' syndrome, so combined with the rest of Mr. Travis's comments on increased wear and binding, I would think the fit would have to be fairly close, not looser. If both post and beam have the same thermal expansion, I would think the bore would only be 1/8" clearance at most and probably 3/32" or less. A looser fit between concentric cylinders is plain lost motion and makes for more/rapid wear and binding, not less. A piston loose in a cylinder will batter itself and the cylinder to death in relatively short order. The pitch/roll relationship between the beam and post/truck frame needs to be kept as close to zero as possible to keep the truck from self-destructing. A three degree pitch would be fairly extreme, but I used it to exaggerate the truck center column's relative motion.

Author:  Ron Travis [ Thu Apr 07, 2016 5:46 pm ]
Post subject:  Re: Early Central Pacific Tender Trucks

Train Detainer,

Thanks for posting more drawings and explanations. I am not sure what to think about the ball and socket joint. I understand your point that the outside of the housing does not look hemispherical in the upper half. In the photo, the upper section almost appears to be cylindrical, but it seems to neck in somewhat, but not to the extent of the lower hemisphere.

I see what you are referring to as a possible rubber insert showing around the top, and appearing to be of a different material than the cast iron of the housing. If that is a rubber liner, it may have a spherical void or a void similar to what is implied by the outside of the casting.

In seeing the cylindrical stem extension of the “ball” feature extending above the housing, and the size of the ball that it implies; I do not see much potential room for it to telescope.

Additionally, if it does telescope, it seems that one would not want it to have the potential to bottom out in that movement. It seems that this would require a potential for at least 2-3 inches of vertical free travel which appears to be improbable. Yet, if it does not telescope, we are back to the proposition of transferring weight to the truck with no direct spring suspension at all. I don't think that the resilient rubber could provide the necessary deflection for the telescoping movement of the ball. So, if there is no telescoping action, the only function of the elliptical springs would be as side bearings, perhaps in a constant contact configuration.

Author:  J3a-614 [ Sat Sep 16, 2017 8:01 am ]
Post subject:  Re: Early Central Pacific Tender Trucks

Just a photo that appeared in another thread, showing these trucks under a C&NW locomotive.


Another engine on C&NW had'em, too. This turned up on a Facebook site, "Pre-1895 Railroads & Steam Engines," posted there by Madison Kirkman (who posts as M.M.C.C.H.S. here):

https://babel.hathitrust.org/cgi/pt?id= ... s.mhs03488

Author:  TrainDetainer [ Sat Sep 16, 2017 11:34 am ]
Post subject:  Re: Early Central Pacific Tender Trucks

J3a - Actually those look like fairly standard 4-point trucks so they wouldn't fit in the same subcategory as the CP 3-point trucks.

The first link is a great picture though. Thanks for posting it.

Author:  Ron Travis [ Sun Sep 17, 2017 12:32 am ]
Post subject:  Re: Early Central Pacific Tender Trucks

There is some topic overlap in this thread, but I have not been able to keep track of where various distinctions begin and end. In post #13 on page 1, I introduced the topic of a specific truck design that has at least some features in common with the trucks mentioned at the start of this thread. Where such commonality cannot be confirmed, however, seems to be in the details surrounding the center of truck pivot, and other details in this same area that are typically hidden from view in most photos showing the outside of the truck frames of the type of truck I mentioned on page 1.

In any case, in both of the photos posted above by J3a-614, the visible parts of the tender trucks do indeed match the details of the type of truck that I introduced on page 1, post #13.

Author:  TrainDetainer [ Sun Sep 17, 2017 2:38 pm ]
Post subject:  Re: Early Central Pacific Tender Trucks

Yes, they do fit your post number 13, but the the thread is titled and was originally about the CP trucks, which (on IID 151 and CP173) are a particular type of 3-point suspension. Most of the discussion was about the design of those CP trucks. I'm just trying to stay on the original topic.

I'd suggest that the distinction is primarily the intricate CP 3-point design, which is different from a 'standard' 3-point design and fundamentally different from a 4-point. Since the 4-point is fundamentally different, it is mostly irrelevant to the CP truck discussion.

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