Triple Heading - Aristo's U25Bs with the SD45

Triple Heading - Aristo's U25Bs with the SD45 Vignette
(The speed difference of Aristo-Craft U25Bs vs the SD45)
April 8, 2007
Revision GE-B
Ted Doskaris

August 27, 2020
Rev GE-B1, Increased resolution of pictures

August 30, 2020
Rev GE-C, Added comparisons of U25Bs since now lowered & equipped with Kadee centerset couplers

The Aristo U25B and SD45 locos exhibit different speeds when run separately on a track with the same power applied. This condition is apparently due to different gearing and  / or electric motor characteristics within their power trucks. None-the-less these locos can be operated together in an “MU” lash up whilst pulling a load such as a train. (With the exception of the GP40, it's to be appreciated that the U25B shares the same motor block design with other Aristo 2 axle locos that include the FA1 / FB1, RS3, RDC1, and Eggliner, and as such one can expect very similar results.)

To see how the different locos work together, I setup a test train that consisted of 25 cars.
The U25B pair as factory delivered did not pull this train without incurring wheel slip on certain parts of my circuitous under house layout that includes mostly 10 foot diameter curve tracks. The single SD45 will pull the train all by itself without any apparent wheel slip.
(For folks who have layouts with long straight track sections and / or very wide diameter curves or have installed additional weights to the locos, longer trains can be pulled than these as originally received factory examples.)

The following pictures depict a consist of Aristo-Craft locos including 2 U25Bs of the older motor block design characterized by fully suspended trucks and an SD45 pulling a 25 car train on my under house layout. This is to illustrate how the speed difference of the U25Bs (being generally faster) work with the SD45 when operating with the 2 U25Bs as lead units, then the trio swapped around when operating with SD45 as the lead unit:

Below is shown the Aristo-Craft loco operation whilst pulling the train with the two SP U25Bs leading the SD45 trailing unit. The U25Bs are of the NON ball bearing motor block types having the old fully suspended trucks:


Years later these locos are now modified by lowering them for a more prototypical look, which also facilitates equipping them with Kadee centerset (no offset) couplers. (Body mount Kadee centerset's had also been fitted to the train cars in place of truck mounted Aristo couplers.)

A lowered U25B with Kadee centerset couplers is shown below


With the method used to lower the locos, their notorious leaning & instability tendency is intrinsically corrected. In this regard, see "Installation Guide Aristo-Craft U25B & CamPac Components" that describes and shows using 3-D printed coupler boxes available via Colin Camarillo's website.


As a further enhancement, about 3 pounds of extra weight was added within the fuel tank for a low center of gravity to improve traction. Accordingly, the motor blocks had been replaced with the newer ball bearing types that can handle the extra weight. These ball bearing motor blocks should be available from Bachmann Trains, or one of their retailers, since Aristo-Craft had gone out of business.

Below, the difference can be seen with the locos as lowered when coupled to the prototypically taller SD45.



The above picture shows a closer view of the coupled U25B to the SD45 after it was lowered.

For comparison, the below picture shows the coupling of a U25B to the SD45 the way it was before it was lowered:

Below is shown the locos before being lowered with swapped direction with the train being pulled by the leading SP SD45 coupled to two U25Bs:


For more of a comparison with a different brand loco, shown below is a USA Trains GP7/9 coupled to a lowered U25B. This is more prototypical since the two locos are of similar height.


Below is shown the top views of the coupler action between the U25B and SD45 with their original Aristo couplers:
(The camera auto focus did not work too well here, but it is still good enough to see the coupler action):

Aristo-Craft loco operation of two SP U25Bs leading an SD45 showing the coupler action at the U25B & SD45 whilst pulling a 25 car train:


For comparison, shown below is the lowered U25B leading the SD45, both equipped with Kadee centerset couplers

Reverting back to the way the locos were, shown below is the SP SD45 now leading the 2 U25Bs and showing the coupler action at the SD45 & U25B whilst pulling the same train: (Note there is no apparent coupler binding or sideways forces.)
Given the coupler action pictures, it does not appear to matter as to placement of the "faster" U25B locos.
Close observation of the wheel sets of all locos show no slippage when starting out or pulling the test train.
The train load appears to integrate the locos' speed difference operation.
In this regard, It would seem that the U25Bs may draw slightly more current and the SD45 may draw slightly less current under such collective operation.
In any event, the track power amp meter shows little current use (approx. 2 amps or less) whilst operating the test train at various speeds no matter which way the trio of locos are oriented.


Comment: Aristo’s U25B stability and is truck mount design.

Some folks have described Aristo's U25B as having a stability problem.
This may manifest itself in the loco exhibiting a wobble or listing / leaning to one side, particularly when the loco is operated on curves.
Since my U25Bs don’t have too much operational time on them, I have yet to experience stability issues, albeit I noticed they do lean on tight curve track.

That said, looking at how this loco is designed by Aristo, it appears to have something to do with its rather odd truck pivot design. This is a design that resembles Aristo's passenger car trucks - that being the offset pivot, but the U25B loco has an added plastic adapter plate, called an eccentric, inclusive of a 4 roller arrangement to apparently reduce friction when the trucks pivot.



This offset pivot arrangement is of benefit for tight curve train operation by reducing the amount of front and rear overhang at the pilots' coupler ends of the loco that projects toward the outside of the curve, albeit with the trade-off of a bit more belly overhang.
That said, it seems some folks with this loco have experienced a wobble or list to one side when rounding curves - maybe because of those rollers wearing or falling out or the wear done to the under side plastic surface of the loco's frame as the rollers traverse this area.

Something else to consider is that adding more weight within the fuel tank area can be expected to improve the loco’s stability as well as its traction - that had been done some years later.

The below pictures are of my Union Pacific U25B that happens to have the newer ball bearing type motor blocks. However, this is not relevant to the offset pivot hardware since all U25B incorporate this design feature.

The pictures may also help with respect to seeing where lubrication can be applied, however, be advised from my experience that the use Aristo's Electralube has been associated with cracked plastic journals on other Aristo rolling stock, so don't use it.

As shown below, the Aristo-Craft U25B loco uses an adapter plate, called an eccentric, with rollers to implement an offset mounting of its 2 axle power truck. This design affords a shorter coupler end overhang from the pilot with the trade-off of more belly overhang that is helpful on tighter curves, albeit with the loco somewhat leaning over.
Below are upside down views:

The Aristo-Craft U25B power truck offset mount adapter plate includes pivot rollers to reduce friction.


Sometimes the eccentric has an assembly defect that causes one or more of its rollers to become ineffective, which can cause the loco's truck to bind and derail going in and out of curves! This is because there may be too much glue on the needle axles that keep the rollers in place. The excess glue can be cut off with a razor knife - example shown below.


Note: To see how to take apart the U25B to get at the eccentric, see "Installation Guide Aristo-Craft U25B & CamPac Components".




Aristo U25Bs Lowered with Kadees Pulling Train Outdoors

(The video starts with a few still images showing issues with the loco's truck mounting design.)