On the trucks of SD-40s, SD-45s, and perhaps other models, the truck side frames rise up as they pass over each axle and drop down a ways as they span the two spaces between the three axles. In each of those two depressed areas of the side frames, on their top surfaces, there is a raised pedestal feature that is cast as part of the side frame. That raised feature appears intended to push or bear in a horizontal direction against another structural member. It is not visually apparent what that other member is connected to. What do these features do? I used to think they transfered the tractive force directly from the side frames to the main frame, but that seems problematic and not feasible.
You can more or less see the features I am referring to in this drawing:
It appears to me that those are a part of the top of the truck which carries the bolster (the pivot for the truck as well as the weight bearing member). I could be wrong …
The standard EMD truck for the SD40-2 and SD45-2 series of locomotives was the HT-C model. It was in production from the introduction of the “dash 2” series in 1972 until about 1994. Following is a link to a Wikipedia article:
I think this is where the truck frame connects to the bolster, by way of the Flexicoils. The bolster is a H-shaped casting, with the center pin above the middle axle, and coming out to these mounts. On this one, the bolster is the H-shaped casting betwixt the “ears” on the truck sideframe, and running behind the traction motor cables. If you look close, you can see the big coil in there. The mounts keep things in place fore-and-aft, yet allow for up-and-down motion. When these trucks wear out, there is a lot of up-and-down motion.[:P][;)]
The truck type is a “High Traction-C” not a “Flexi-Coil” type. The bolster pads are made of sandwitched rubber and are intended to control lateral motion of the bolster (and carbody). The bolster sits on the 4 pads which transfer the locomotive weight to the truck side frame. There are “stops” on either side of the bolster arm that act to transfer tractive forecs from the truck side frames to the bolster and locomotive carbody. Both the bolster arm and the “stop” contact surfaces are fitted with plastic contact plates that add friction snubbing to the lateral control action of the rubber bolster pad. On some locomotives used in high speed freight service (70 mph) there is a lateral shock absorber applied between the bolster arm and the “stop” fixture on the truck side frame to increase snubbing of lateral motion which in turn reduces locomotive carbody yawing. Keeping carbody yawing to a minimum reduces physical damage to locomotive components and improves ride quality for the crew.
The Wikipedia article linked above contains an interesting claim regarding the derailment-prone Amtrak SDP40Fs - that those incidents were the results of a hollow bolster casting that was specified by Amtrak to reduce the truck’s weight (account of the added weight of the steam heat generator and water tank for same that was required then in that pre-HEP era). The article goes on to state that those derailments - which tended to be predominantly of either the widened gauge and/ or rail roll-over variety - happened at the second SDP40F in a consist and the trailing baggage car - and that the baggage cars were blamed !
For those who don’t know, this was a problem with the SDP40Fs - which was discovered the “hard way” - shortly after their introduction into se
I second that. I find trucks to be one of the most fascinating and least explored features of diesel locomotives. I would love to see a big article covering the wide variety of locomotive trucks with detailed illustrations and design objectives. I do recall an article in Trains about the Blomberg truck. That series on the three-piece freight car truck was one of my favorites.
OK - done ! (see copy following). I submitted it via the “Contact Us” link below, and selected the “Railway Post Office - Letters to the Editor” option, as that seemed to be the most suitable (though not completely so) for this purpose. If anyone knows of a better or more dircet way to do that, please advise. Let’s see what happens.
Interesting thread - thanks for starting it.
Paul North.
"Article Suggestion:
Both “Bucyrus” and I think that “Locomotive Trucks” would be a good subject for a feature article. For more information, see the current discussion under the thread with that reference at:
If you read my profile you will get an idea about how I may know some design details about locomotive trucks that are not commonly known. From 1989 to 1991 I led the Union Pacific/EMD team that resolved the locomotive yawing and ride quality issues of the SD60. I had a close relationship with the EMD Truck Design team and have had the opportunity to literally pick every detail of the HT-C truck apart as well as to fully instrument every moving part to get a ride profile of the truck as the locomotive traveled at 70 mph pulling a wide variety of trains throughout Union Pacific main lines.
I let a similar Union Pacific/GE team that resolved problems with their HI-AD truck on Dash 9 and AC4400 locomotives in 1994. The placement of shock absorbers and yaw dampers on the HI-AD truck was the result of the tests. When we started, the instrument data showed that the wheels were hunting from flange to flange across the rails, when we finished wheel lateral movement did not exceed 1/4 inch on tangent track or in curves.
I agree that an article on locomotive trucks would be very interesting. I believe that both EMD and GE take pride in their designs and would be willing to contribute to the article.
About the mention of the bolster of the HTC truck on SDP40F; all bolster castings that I have seen on HTC trucks are “hollow” as are the truck side frame castings. It would take considerably more steel to cast a solid bolster or truck frame and would also make it dificult to handle the bolster or truck frame for machining, motor changeout, etc.
Wow ! I’m impressed. I hadn’t taken the time to read your profile earlier, although your first post above clearly demonstrated technical knowledge and mastery of the subject. Now we have an real expert here - great !
I hope the editors of Trains consider contacting you to write such an article.
Feel free to add in just about anything you want, and take this thread wherever you want to go with it. I think you’ll find there’s quite a thirst here for this kind of technical knowledge, and it’s not too likely [;)] to get tangled up with politics, economics, or some of the other contentious aspects of the business that sometimes creep into the other threads.
Looking forward to whatever you choose to post. Again, welcome !
Thank you tleary01 and others for the answers to my original question. As I understand it, the truck bolster is an “H” shape with the center bearing resting on the center of the “H” crossbar. The four endpoints of the “H” are transferring the weight directly to the tops of the truck side frames. Apparently the points of this weight transfer are hidden from view. What are visible are the load transfer points or “stops” that transfer the truck pivot to the bolster.
Thank you tleary01 and others for the answers to my original question. As I understand it, the truck bolster is an “H” shape with the center bearing resting on the center of the “H” crossbar. The four endpoints of the “H” are transferring the weight directly to the tops of the truck side frames. Apparently the points of this weight transfer are hidden from view. What are visible are the load transfer points or “stops” that transfer the truck pivot to the b
If I could, I’d like to pick your brain a little bit on what is probably not a proprietary or sensitive topic, and one that is beloved by most fans - the UP"s 40-year old DD40AX “Centennial” series, and esp. No. 6936, as follows:
I would think that those D-D trucks and long locomotive wheelbase provide a very smooth ride and tracking, although maybe at the expense of accelaerated wheel flange wear in territory with lots of curves. Can you comment at all on that ?
[Sometimes I can be really, really slow to pick up on some things - just ask my wife ! Anyway . . . ] Like most people, I’d always thought of the DD40A’s as just 2 of the SD-40’s on a single frame (actually, at 6,600 HP, it’s more like 1 - SD40 plus 1 - SD45). But over lunch, when framing the above question, it finally dawned on me that there are a whole lot less powered axles - and hence a lot more HP per powered axle - than what a straight proportion would provide from a simple doubling of everything. Specifically (and feel free to correct my numbers if they’re not right):
DD40A is 6,600 HP / 8 axles = 825 HP per axle.
But almost everything running today is 4,300 or 4,400 HP max. on 6 axles = 733 HP per axle, so the DD40A is 92 HP per axle on 12.5 % more per axle, which I think is significant. The only other mass-produced diesels I can think of that were that high or higher are GE’s U33B and U36B models - 825 HP and 900 HP per axle respectively. So:
a) Does that HP/ axle ratio cause any unusual operating, wear, or maintenance characteristics ? (aside from being in the 4-axle rigid truck as already mentioned above) How “slippery” was this class compared to others - say, a regular SD40 or SD40-2, or the “Fast Forty” series ? Anything else unusual about them ?
You are correct in the orientation of the truck bolster. The bolster of the HT-C truck has a “center bearing” that receives the locomotive “center casting” The inside of the bolster center bearing the bottom is lined with a flat do-nut shaped plastic wear plate and the sides are lined with a 2-piece plastic ring to separate contact of the metal surfaces. The center casting is lubricated with bearing oil.
This same description is true of GE standard 6 wheel trucks used on locomotives prior to the introduction of the HI-AD truck in the early 1990’s. Like the HT-C truck the boster is set on 4 rubber sandwich pads and has stops to transfer the truck forces to the bolster but they are to the inside of the rubber pad and not visible in a photo of the truck from the outside.
The EMD Radial Truck and the GE HI-AD and GE Radial trucks have 4 rubber sandwich pads between the locomotive carbody and directly to the truck side frames, they do not have stops, they transfer the locomotive weight to the truck and control lateral motions. Tractive or Dynamic Braking forces are transfered to the locomotive frame with a “Traction Pin” that connects the center of the truck frame to the locomotive frame. The traction pin is located between motors 1&2 on the front truck and between motors 5&6 on the rear truck. Only a top photo of the truck would will show the traction pin location.
Drawings and photos of the EMD HTCR Truck can be found in the Sixth Edition Car and Locomotive Cyclopedia page 510, the GE HI-AD Truck is shown on page 537.
The DDA40X was such a unique locomotive in many ways that your questions are only th “tip of the iceberg” ans my answers will probably generate more questions. How about moving your questions to the Locomotive Forum with a new thread or add to the existing thread about the DDA40X.
In my recollection the DDA40X locomotives did ride good though they would take on a vertical bounce at 70 - 90 mph. I m not aware that the wheels had significant flange wear problems but the DDA40X did get wheel trued more often than other locomoties due to the high mileage they traveled.
When you look at a 3 axle truck and then a 4 axle truck you might think that the longer wheel base would cause more dificulty for the wheels to negotiate a curve. On main line curves the trucks do not swivel as they would if the locomotive was on a tight curve like a turning Y. The wheels and axle have lateral movement that allows them to follow the curve in much the same way a rigid frame steam engine moves through a curve.
The closest comparison to the DDA40X is to see it as 2 GP40-2 locomotives sharing the same frame. The 16 cylinder engine has increased horsepower from 3,000 to 3,300 due to increased RPM, 900 RPM = 3,000, 950 RPM = 3,300. The DDA40X also has a larger main generator, AR12 that produces higher voltage and amperes.
You are right about the higher horsepower per axle that could cause more tendency for wheel slip. Howerver the DDA40X did not produce full motor horsepower below 28 mph since it did not make transition. By 12 mph traction horsepower was about 1,000 but motor amperage was 1500. Also the axle/wheel weight was higher than other locomotives at the time. The nominal weight of the locomotive is stated at 540,000 lb with 1/2 fuel and sand. With a full fuel tank and full sand boxes the weight was 576,000 lb or 72,000 lb per axle. Even today only CSX is operating their ES44 locomotives at 72,000 lb per axle.
The DDA40X traction motors were D77X3 type designed specifically for that application. They held up very well at the high horsepower and high amperes, the motors did ge
