USAT SD40-2 experiences, including Kadee centerset couplers - and a whole lot more!

USAT SD40-2 Experiences, including Kadee centerset couplers - and a whole lot more!

Ted Doskaris
Initial Release, A
April 11, 2020

Rev. B,  Added Locos' side grill illustration & another video
April 15, 2020

Rev. C, Added illustrations and loco speed test info. with another video
April 21, 2020

Contents:

Overview
New Southern Pacific SD40-2
Optional Snow Plow
Union Pacific SD40-2 Reconstituted
New Motor Blocks
Sideframes
Wheels & Traction Tires
Truck Assembly
R & R Body Shell / Chassis
Chassis Dog House
Switch Board & Cables
Motor Current In-rush Resistors
Kadee Centerset Coupler & Box Choices
Installing CamPac BoxesTM
Installing Datum Precision Metal Boxes
Installing CamPac Pilot Plugs
Installing Detail Parts & Railings
Installing Extra Weight
Comparison of USAT SD40-2 & Aristo SD45
Battery & "Wet Noodle" SD40-2 Chassis Fix!
Videos

Overview

The USA Trains SD40-2 is a 1/29 (G scale) locomotive having 3 axle trucks.

This vignette (article) is lengthy and includes about 70+ illustrations, most of which are condensed having several pictures with annotations - so there may be as many as 300+ pictures complied for this vignette.

For brevity, in some cases the SD40-2 may be referred to as SD40, recognizing that prototypes have differences.

Described will be example methods for removing & attaching the body shell, assembling a motor block, replacing an axle, adding weight, fabricating & installing replacement cables (that connect trucks to switch board), adding motor current inrush resistors, installing Kadee centerset couplers (utilizing 3-D printed plastic boxes or CNC machined metal boxes), and installing detail parts, including railings, folding steps, MU connectors, exhaust stack, and hoses. Also, comparisons will be made with the Aristo-Craft SD45 as to size and 3 axle trucks.

This vignette will mostly focus on experiences gained over many years primarily borne from the following 3 SD40-2 locomotives:

(1) A newly purchased Southern Pacific unit
(2) An acquired used Union Pacific unit that only included body shell and chassis (which did include circuit boards) that has been reconstituted to operating condition by obtaining many missing parts.
(3) A friend's used Southern Pacific unit that had been previously modified for battery operation in a fashion that resulted in "wet noodle" chassis flex - that had to be corrected to reliably accept body mounted Kadee couplers and operate on a layout without a tendency to uncouple.

All the units have been equipped with body mounted Kadee centerset couplers and parts, but not the boxes & screws, from Kadee 907 kits. Accordingly, 3-D printed "CamPac" parts, including plastic coupler boxes & mounting pedestals are utilized.

These parts are designed by me (Ted Doskaris) in concert with Colin Camarillo who has the 3-D printer and software expertise to implement them. SD40-2 parts (and other applications) can be obtained from Colin by contacting him via his website.

Alternatively, CNC machined black anodized aluminum boxes, shown below, designed by me in concert with John Jans of Datum Precision are available as an option to install on the SD40-2. A dedicated 3-D printed mounting pedestal & discrete fairing are required to be used with this box. The Datum Precision metal box and pedestal & fairing can also be obtained by contacting Colin Camarillo using his website.

The tail on this box will need to be cut short to fit the SD40-2 application - described later.

The SD40-2, when equipped with either plastic CamPac BoxesTM or Datum Precision metal boxes, is intended to operate on 8 foot diameter or greater track curves. However, layouts with "S bends" must have a straight track section the length greater of the of the loco or longest coupled car between opposite diverging paths. A 2 foot straight track may be acceptable.

New Southern Pacific SD40-2

Shown below is the SP SD40-2 as received new.

The SP unit included factory mounted standard hook & loop couplers.

The side and end railings are to be user installed.

Optional Snow Plow

The snow plow is to be user installed and described in vignette, title: "USA Trains SD40 Snow Plow Relocation for Pragmatic Layout Operation"

The plow's mounting as designed is too low having a propensity to make contact with less than perfect track work that can cause it to be knocked off and damaged!

Union Pacific SD40-2 Reconstituted

Because this unit had the most issues to contend with, it will serve to describe many of the examples.

I purchased this unit used for about $75, albeit stripped of trucks and virtually all detail parts:

USA Trains has an excellent parts department with Mike there being very knowledgeable to the extent of providing some non listed items. Over time I obtained most of what was needed. The labels on the received parts bags with quantities & cost are illustrated:

The parts cost were about $310 not including shipping, so with the initial body shell & chassis purchase of $75.00, the total cost was somewhere about $400 to reconstitute the loco. Looking at ebay SD40-2 offerings, when available, they typically cost more than $400 when finally sold.

New Motor Blocks, as Received

Normally, the 3 axle trucks would be expected to include the metal plate attached to the pony (floppy) axle, but I had to get the plate with its unique hardware and chassis attaching screws as separate items!

The plate with its hardware is to be attached as illustrated below:

The plate on the pony axle of the motor block is to be fastened to the chassis with 4 unique, very short, screws having intrinsic washers. A close up view of this is shown below

Conversely, the motor block itself can be removed from an installed truck by removing the 4 plate screws and then separating its sideframes to expose the axle tips so it can be withdrawn. The wires can then be unplugged from the pins on the back of the block to free it up. This is the conventional way to service an assembled loco without having to take it apart.

Sideframes

For the Union Pacific loco the sideframes are factory painted silver, so they are very noticeable where attached to the A frame. I chose to paint that area black.

Sideframes needed for the Union Pacific SD40-2 were obtained from USA Trains parts. Each sideframe included a jumper wire between the two eyelets for electrical pickup when the motor block axle tips are engaged, but they needed to have a wire with JST connector* soldered to the end eyelet for interconnecting to the switch board within the chassis.

*(Note: Factory wired sideframes are spliced with respective wires that connect to the back of the motor block pins dedicated for the skates, and they then employ a single JST connector that plugs into mating power pickup receptacle wired to the switch board ("PICKn") within the chassis. I chose to use a dedicated JST connector for the sideframes that would plug into an added, spliced in, mating "PICKn" receptacle within the chassis.)

Because the UP loco sideframes had been factory painted silver on both exterior and interior sides, their wires & eyelets bushings were painted, too, which had to be cleaned off from the end eyelet in order to tack solder on the connector pigtail wire. However, I discovered the silver paint did not seem to be a problem when soldering, possibly because it has metallic particles in the paint formula that conduct heat.

The process used to solder the JST connector pigtail pair to the sideframes' eyelet is Illustrated below.
For consistency, the wire color applicable for left and right sideframes was chosen to match the factory colors observed on my factory wired "new" SP SD40-2 truck.

Wheels & Traction Tires

The factory 3 axle motor is comprised of two sections: a self contained 2 axle section and a self contained pony (floppy) axle section with connecting drive mechanism from the 2 axle section.
The motor block 2 axle section typically comes with its end axle wheels fitted with rubber traction tires resembling a rubber band embedded in its tread groove. The center axle wheels are solid metal. The opposite end pony axle metal wheels are electrically dead.

With the truck mounted on the chassis, the end axle with traction tires can be lifted out for replacement.

Primary electrical pickup of the 3 axle motor block is by its spring loaded skates that rub against the railhead and its center axle wheel treads that touch the railhead having an electrical path via axle tips engaging the sideframe eyelet bushings.

The skates with integral spring can be removed by just lifting them out when the motor block cover is off, but they are an essential contributor for track power pickup in the SD40-2 loco, however, battery users would be more likely to eliminate them.

The skates and sideframe eyelets are electrically connected together externally away from the truck

It is to be appreciated, too, that unlike the USA Trains 2 axle motor blocks in the F3 and GP units, there is no spring wire that touches the axles within the motor block housing that would provide an additional conduction path connecting to the skates. Also, the pony axle wheels do not have axle tips like other wheels and don't electrically contribute at all.

Traction Tire PROS:
These wheels are advantageous for enhanced pulling ability that otherwise adding extra weight to the loco would provide. Moreover, the motor block & sideframes that it's suspended in both have brass bushings. Consequently, bushing wear, primarily in sideframes that support the loco's weight, should be minimized compared to adding extra weight to improve traction. This configuration would seem best for battery power users.

Traction Tire CONS:
For track power users, wheels with traction tires tend to smear dirt on the railhead which is not good for electrical conduction. Though a rubber tire may last long, when it deteriorates over time, it would deposit disintegrated rubber mixed with dust & dirt on the railhead. The skates used for electrical pickup would also be relied on to help plow the dirt away, but needed pressure exerted by their light springs may be overwhelmed. Most importantly, the rubber tread is an electric insulator, so only during the happenstance operation on a layout - mostly on curve track owing to flange contact - would traction tire wheels be expected to electrically contribute. Hence, for track power users the rear axle having traction tires is best replaced with the same axle used in the center having solid wheels. The more points of electrical contact on the railhead, the less current would result for each point of contact - albeit not necessarily distributed equally. The benefit is to reduce the tendency for wheel & skate pitting and minimize the possibility of sputtering operation.

Shown below, an example axle is lifted out of a motor block - to be replaced with an axle having solid wheels. When installing the replacement axle, ensure its bushings are oriented like described and shown in the prior picture.

Illustrated below, the replacement axle with solid wheels obtained from USA Trains parts to be installed in the motor block is shown with measurements for anyone interested. It's the same as the motor block center axle wheels. The wheel tread diameter when scaled up is undersize by about 10% compared to a prototype wheel.

Truck Assembly

The truck is comprised of sideframes that attach to the plastic "Truck Mounting Block" (aka, A frame) and metal "End Bracket" with the motor block axle tips suspended between the sideframes' eyelet bushings.

The truck must be properly assembled in order to access chassis / body shell attaching screws as illustrated below.

When working on a loco with the body shell removed, a truck can be completely preassembled for mounting on the chassis that includes its sideframes with wire connections - assembling illustrated below.

The whole truck assembly is installed on the chassis as illustrated below.

R & R Body Shell / Chassis

Fastener Screws:

Because the screws were missing on the Union Pacific loco, substitute metric M2.5 by 12mm screws were obtained from UXCELL via Amazon.com. Since the body shell had already been prethreaded with factory self tapping screws, it's behooving to use self threading screws without a tap flue to avoid cross threading the existing threads.

Illustrated below are the points of attachment using the Union Pacific unit example.

A close up view of the chassis area with fuel tank removed is shown below.

Shown below is a better close up view of the front truck. Note how the truck's metal bracket needs to be tilted to access the chassis screws.

Chassis Dog House

Behind the left side of the cab is a vertically mounted "Electrical Cabinet Air Filter" box that I call a Dog House.

The Dog House may become dislodged or lost when handling or working on the loco.

If needing a replacement Dog House, contact Colin Camarillo via his website to obtain a 3-D printed replica.

Switch Board & Cables

The switch board is the printed wiring board (PWB) fastened within the chassis interior that has 4 slide switches to enable or disable the truck motors, lights, smoke unit and sound unit power (if installed). The switches located near the back of the front truck are actuatable from the underside of the chassis. The PWB should include interface wiring with JST connectors that connect to the front and rear trucks. The wires for the rear truck "MOTOR2" and power pickups from wheels & skates ("PICK2") were cut off the PWB on the Union Pacific loco, so cables had to be obtained.

For consistent interchangeability, it's prudent to make substitute cables having connection wire colors the same colors as on a factory unit like my "new" Southern Pacific SD40-2 as illustrated below.

When matching wire color connections on the switch board (PWB), it was discovered remaining tailings of the PICK2 wire colors were swapped. If the cable is connected to the rear truck having corresponding wire colors, there would be a power short circuit when the loco is put on the track when track power is applied! This was discovered belatedly during testing the loco on a track. Perhaps the original loco owner had a rear truck with different wire color assignments, prompting the thought of inconsistent factory assembly - a practice common to competitor, Aristo-Craft, now defunct!

Illustrated below are the substitute cables with their connections to the switch board.

Note the above picture shows 4 different connectors with colors emanating from the body shell being numbered so they can be identified to sockets they mate with on the PWB.

After all interconnect cable wires were soldered on the PWB, the switches were preemptively cleaned as illustrated below. (I had experienced USA Trains GP7 like kind switches that exhibited open circuit conditions that were resolved by using DeoxIT D5.)

The slide switches were actuated back & forth during the cleaning treatment.

Motor Current In-rush Resistors

Well known documentation authored by George Schreyer (engineer / scientist) describes the characteristics of USA Trains electric motors having large initial current draw when operating on pulse width modulation (PWM) that can result in wheel pitting. PWM is common on many model train controllers or within some electronic devices that interface with the motors.  A simple fix to mitigate wheel pitting is to a add a very low value resistor in series with each electric motor. The speed of the loco is slowed some, but this can be beneficial when MU operating with slower running locos like the Aristo-Craft SD45.

Illustrated below are 1 ohm resistors used for limiting inrush current obtained from UXCELL via Amazon.com.

The two resistors needed were installed on the Union Pacific loco. Finding a good place to install them is illustrated below.

A closer view of the stacked resistor pair is shown below.

Speed Affects:

The intent of adding the motor current in-rush resistors is to mitigate wheel pitting and desirably not to affect loco speed; hence, low value resistors are used to accomplish this purpose, but a side affect is the loco is minimally slowed. Using higher value resistors to purposely speed match other slower running locos would be expected to degrade pulling ability.

Speed tests of the UP SD40-2 loco with 1 ohm resistors were compared to other, different, Aristo-Craft SD45 & GP40 locos are shown in a video near the end of this vignette.

Speed tests of an SP SD40-2 loco WITHOUT resistors were compared with two GP38-2s with & without 1 ohm resistors operating on DC linear and then pulse width modulation (PWM). These are shown in another video near the end of this vignette.

Results Summary & Comments:

When tests were done with a USA Trains SD-40-2 having motor current in-rush resistors (that runs faster even with the resistors than the ultra slow Aristo-Craft SD45), the SD40-2 & Aristo SD45 operated satisfactory when coupled together. Likewise, when tests were done with a GP38-2 that runs faster than the SD40-2, they operated satisfactory when coupled together. (USA Trains GP7/9, GP30 & F3s have the same motor blocks as the GP38, so results would be the same.)

When a slower loco is coupled together with the faster loco (gross disparity not withstanding*), particularly when pulling the weight of a train, both locos tend to equalize (wheels turning in unison) whilst the slower loco may draw somewhat less current with the faster loco drawing somewhat more current.

As an added fail safe, it's desirable to replace axles having traction tire wheels with ones having solid wheels.
This has 2 benefits:

1. Wheels are allowed to conditionally slip so they can spin with consequential motor speed generating back electromotive force (emf ) for less current draw, thereby, reducing the risk of motor burnout.
2. For track power users, additional electrical pickup distribution points from the railhead are afforded which minimizes individual wheel tread deterioration (pitting via electric arc or PWM) and lessens the chance of sputtering operation. If needed, "MUing" another loco makes up for loss in pulling ability.

*An example gross disparity speed difference is operating the fast USAT SD70 with the ultra slow Aristo Dash-9, etc. 6 axle locos. The worm drive and gear teeth mechanisms of these locos fight one another with audible protest, which and can result in damage.

Kadee Centerset Coupler & Box Choices

Centerset couplers (having no upward or downward offset) are to be installed on the SD40-2 locos for their prototypical realism and superior performance characteristics. (Kadee couplers normally used for the SD40-2 have an upward offset to avoid having to do any changes to the loco, but they just don't look good and can have too much flex during operation.)

To accommodate centerset couplers, the front and rear pilots of the loco must be notched - a fairly simple task. CamPac 3-D printed boxes, with integrated fairings, (or CNC machined metal boxes with discrete plastic fairings) are used on the examples described herein. Also, CamPac 3-D printed pilot plugs are used to cover the large ugly opening (meant for hook & loop couplers) in the lower pilot area.

An example SP loco fitted with the CamPac parts and Kadee centerset couplers is illustrated below.

When using the snow plow, it covers the large opening in the pilot, but a plug still could be installed.
For modifying & mounting the plow, see vignette, title: "USA Trains SD40 Snow Plow Relocation for Pragmatic Layout Operation", "Snow Plow Modification" therein.

Before installing some parts on the loco, including CamPac parts, it's preferable to prepaint them.

Installing CamPac BoxesTM

For detail instructions, see " Installation Guide USA Trains SD40-2 & CamPac Components" hosted on Colin Camarillo's website.

That said, much of the process will be summarized here.

First, remove existing hook & loop couplers with their pedestals (or other aftermarket couplers & parts), being sure to save the factory mounting screws.

WARNING: To make the pilot cuts, it's much safer to do this by hand with a small razor saw and files rather than a powered Dremel cutting wheel that tends to grab & jump resulting in unintended damage.

Keep in mind space is limited with the motor block installed, so it could be temporarily removed or lifted out and set aside the loco with its wires still connected.

To minimize cutting debris from getting on loco parts, a cloth or paper towel should be used to cover areas of concern.

Illustrated below is how the pilots can be notched out.

Installing the CamPac Pedestals:

Mounting the CamPac 3-D Printed Plastic Boxes:

Installing Datum Precision Metal Boxes

When using the very strong metal boxes, dedicated CamPac pedestals that include a post and discrete fairings are employed. (Like 3-D printed plastic boxes, all these items can be obtained by contacting Colin Camarillo via his website.)

It's preferable to mount the pedestal and coupler box and level it with the Kadee coupler height gauge before installing the pilot plug, otherwise expect some manipulation to insert and fit the box tail hole over the pedestal's post.

Because the metal box was designed for many applications (mostly for Aristo-Craft locos) its tail is to be trimmed (cut short) with a hacksaw for the USAT SD40-2 application here.

Preinstall coupler, springs, and lid (but not with Kadee screw) from the Kadee 907 kit into the trimmed metal box before mounting it. (A #2-56 flat head screw is used to fasten the Kadee plastic lid to the box.)

Installing CamPac Pilot Plugs

These are used to cover the big ugly opening at the bottom of the pilot for a more prototypical and aesthetically pleasing appearance. If using the optional, extra cost, snow plow, they won't be needed because the plow will hide the opening. However, because USA Trains packages 2 plows in a bag for this option, you may choose to only put one plow on the front nose of the loco like many prototypes whilst using the CamPac plug on the rear of the loco.

The plug will need to be glued from the back side of the pilot if it does not friction fit - illustrated below.

Installing Detail Parts & Railings

These parts include the Exhaust stack, MU connectors, Folding Steps, Coupler Lift Bars (aka, cut levers), Railings (including Pilot Railings & long Side Railings), and Hoses.  Some of the parts are best prepainted before installing them.

Exhaust Stack Installation:

This is a simple part made of shiny black plastic when obtained from USA Trains parts. Being its an exhaust part, its logical to be black - though when on factory new locos they can be body color.

The stack is typically friction fit mounted near the front on the dynamic brake housing.

MU Connectors Installation:

The MU connector typically press fits into the slot at the chassis front and back porches.
If it fits too tight, the paint buildup on the its tab or in the chassis slot may need to be clean off.

Folding Steps Installation:

If the mounting pegs on the hinged edge of the step fits too tight in the chassis slots, paint buildup on its pegs or/and the chassis holes may need to be clean off.  Also, the side edges of the step may need to be clean of some paint buildup so it can fold up.

Railings:

Railings are factory made with hardened wire rod having captive stanchions. The rod is susceptible to break if attempting to bend it. Paint used on the railings seems to keep the stanchions in place for proper positional spacing done by the factory.

When fitting railings on the unit, there is a tendency for the end railing stanchions to fit tight on the pilot, whereas, side railing stanchions tend to fit loose. This may vary depending on how much paint the factory uses on the railings or gets into slots & holes where the railings are inserted.

Pilot Railings Installation:

Illustrated below is an example method to mount the end railings.

Side Railings Installation:

Illustrated below is an example method for mounting the side railings.

One unusual experience was with factory placement of stanchions on the Southern Pacific unit - shown below:

For touch up paint, I discovered Tamiya XF-63 German gray was a close match for some SP gray locos, but factory loco paint shades may vary from different production runs.

Coupler Lift Bar Installation (Cut Lever):

The cut lever is made of hardened wire rod which is susceptible to break if attempting to bend it. Plastic eyelets are to be slid on the cut lever and can split when pushing them around the sharp corners.

Also, there is a tendency for the plastic eyelets that hold the cut lever on the pilot end of the loco to fit loose. Furthermore, eyelet pegs seem to bottom out when inserted into some of holes before the outside of the eyelet fully seats. If so, first check the holes for blockage; filing off a little material at the tips of the eyelet pegs can help.

Illustrated below is an example method to fasten the cut lever on the pilots.

Hoses Installation:

In the case of the Union Pacific loco, the proper SD40-2 hoses were not available from USA Trains parts, but GP38 hoses were available and used as substitutes.

The method of installing hoses is the same irrespective of what hoses are used when putting them on the front & rear pilots of the SD40-2 - illustrated below on the UP loco.

Installing Extra Weight

An example SP SD40-2 measured 9.8 pounds before adding extra weight is illustrated below.

For track power users that replace the traction tire wheels with axles having sold wheels (to enhance power pickup), a couple extra pounds should be reasonable to add to the SD40-2 for improved traction.

Without having to remove the body shell, additional weight can be attached to the chassis using a toggle bolt within the fuel tank area, albeit limiting space if using a sound system speaker.

Added are three Simpson foundation plates, P/N BP 1/2 -3 (obtained from Home Depot) to the Union Pacific loco - exampled in the below illustration.

To allow access to the 2 chassis / body shell screws without having to remove the plates, the plates can be drilled out in those locations just enough for screwdriver insertion.

The UP loco now at about 11 & 1/2 pounds is now about 1 & 3/4 heavier - illustrated below.

Comparison of USAT SD40-2 & Aristo SD45

It's understood that Aristo-Craft has been out of business for several years whilst USA Trains survives to date, but Aristo had prolific manufacturing over many years, so significant quantities of SD45s (and siblings GE Dash-9 & EMD E8/9 and GP40) are out in the public and do show up on the used market from time to time, albeit at high prices.

All of these locos have 3 axle trucks (except GP40), but they significantly differ as to how they operate even though they are specified to work on 8 foot diameter track. In this regard, when tested separately & then together on a track, the USA Trains SD40-2 runs notably faster than the Aristo SD45, but fairly close to an Aristo GP40 having 2 axle trucks, albeit with similar ball bearing "prime mover" motor block elements of the SD45.

With the 1 ohm motor current in rush resistors installed in the SD40-2, it was slowed just enough so it would better operate as a cohesive SD40-2, SD45 & GP40 3 unit set pulling a heavy train. (In spite of the individual speed differences, the USA Trains and Aristo locos tend to equalize with all wheels turning at the same time when pulling a heavy train).

Illustrated below is a comparison of the USAT SD40-2 and Aristo SD45 3 axle motor blocks.

Illustrated below is an exterior comparison of the USAT SD40-2 and Aristo SD45.

A close up view of the cab tops is shown below.

Illustrated below is a comparison of the USA Trains SD40-2 side grills.
Note how the USAT SD40-2 has molded in plastic side grills whilst the Aristo SD45 & GP40 have much more realistic wire mesh grills.

Aristo came a long way as to physical realism and mechanical & electrical development in its later years, but did not seem to hold its consistency of quality as well as USA Trains, so at times customers were to discover problems and "fix" things.

Battery & "Wet Noodle" SD40-2 Chassis Fix!

Friend, Colin Camarillo, had acquired a used Southern Pacific USA Trains SD40-2 that had been converted to battery power having a remote control RF receiver. Though the former owner had done several thoughtful nicely done modifications, the loco was compromised as to operating consistently when body mounting Kadee centerset couplers on it.

The reason is how the chassis and body shell long hood had been gutted to fit a Gel Cell battery and added electronics.

To wit, to make the long hood removable it had been severed from its lower structure that normally extends under the cab - with the hood now only held by gravity in order to conveniently access the battery and electronics on the chassis.

Consequently, the chassis and body shell were gutted of factory critical fastening points that affect loco rigidity. The result is the chassis would flex and sag in the middle. Even a slight amount of flex and sag can be a problem because of the SD40-2's long length and excess end overhang from its offset truck centers.

Using sloppy hook & loop couplers would mask operational problems, but the loco had to be fixed when mounting Kadee centerset couplers - of course using CamPac coupler boxes.

The loco as modified by the prior owner can be seen in the illustration below.

Shown below is how the prior owner cut out a large hole in the chassis for additional air flow and mounted an electric fan behind the cab. The fan would supply cooling air to the electronics, but it's intended to cause the shell's roof fans to rotate, too.

The illustrations that follow show how the "wet noodle' chassis is restored to rigidity by using metal stiffeners. This is doable because nearly all the chassis posts had been cut off along with the humps for smoke unit connections, leaving an unobstructed surface for placement. (Battery users typically eliminate smoke units because of high current draw.)

The front and back of the long hood will be attached to the chassis since those attaching points within it were intact. Battery access will be afforded by having a removable dynamic brake blister - described later.

Illustrated below, the rear of the long hood is to be attached to the chassis using metric M2.5 threaded rod as studs & M2.5 nuts - obtained from Grainger.
The studs are threaded into the hood's intact posts and trimmed for proper length. Studs are used here because the corresponding mating chassis posts for mounting had been cut off, so the studs will extend thru the chassis underside where bushings and M2.5 nuts will serve to attach the hood.

The installation process is shown within the below illustration.

As seen in the above illustration, the front of the hood is fastened to the chassis like factory intended using screws, albeit longer for improved holding. This was doable because both hood and chassis mounting posts near the cab were intact.

Fastening the rear chassis nuts on the rear studs with truck in place is done with method using a 5mm nut driver - shown below:

The Metric 5mm nut driver is put to use to attach the rear of body the long hood:

A Long shank Phillips screwdriver is put to use to install longer than factory screws at the front of the long hood.

Accommodating upgrade to Lithium Ion battery:

A long plastic spacer block at the same height of the plastic square channels is used to level the surface for a wider foot print that may be needed with a different battery type. The spacer is pressed in and removable so a Gel Cell battery can still be used. The channels were not removed because they serve as conduits for wires and are spaced so the original Gel Cell battery is "squeezed" between them to retain it.

Removable Dynamic Brake Blister to access battery:

Because the long hood is now fastened to the chassis, the dynamic brake blister now provides access. The rearward facing blade fuse is now moved forward for its accessibility, too.

Illustrated below is the completed result with body mounted CamPac BoxesTM fitted with Kadee 907 centerset knuckle couplers.

Detail parts and railings will need to be installed on this loco after Colin completes the AirWire programming interfacing and upgrade to Lithium Ion battery.

Videos

Speed Tests of SD40-2 with other Aristo SD45 & GP40 locos:

USAT SD40-2, with Aristo's SD45 & GP40 in a 3 unit set pulling a heavy train on layout:

Speed Tests of SP SD40-2 with a pair of GP38-2 locos:

The SD40-2 in this test does not have motor current in-rush resistor installed.
The setup for this test is illustrated below.

SD40-2, & Two GP7/9s in a 3 unit set pulling the same heavy train on layout:

Next to be shown is the UP SD40-2 with motor current in-rush resistors installed operating with a pair of GP7/9s, also, with motor current in-rush resistors installed. (These GP7/9 Geeps use the same motor blocks as the GP38, GP30, and F3s.)
Shown in the video below is with the train pulled by the USA Trains UP SD40-2, but now coupled to 2 USA Trains GP7/9s ("Geeps") in place of the Aristo locos. The speed difference between the SD40-2 and Geeps is less different than an Aristo SD45, so there is no problem when coupled together pulling a train.

Done - and Ready to run !

End
-Ted