# USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.



## Ted Doskaris (Oct 7, 2008)

*USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

USA Trains GP 38 - Mods for Kadee Centerset Coupler Install, Abandoning Traction Tires, Etc.
Ted Doskaris
March 24, 2012

The USAT GP38 diesel in Rock Island Blue Livery (factory boxed) is shown below as I received it.

The USAT GP38 example here is in the Rock Island blue livery - the attractive and last paint scheme the Railroad used prior to its final liquidation in April 1980.










The GP38 comes standard with hook & loop couplers mounted - as seen in the pictures below having taken the loco out of its foam packing.
Note the large slot opening in the pilot required for this type coupler to swing - good for running the loco around the Christmas tree.









*Centerset Couplers*

This is my first USAT 4 axle diesel loco. I chose to use Kadee centerset type couplers because they are best suited for pulling heavy trains since they will avoid levering under load like the offset version Kadee delegated for this loco may do. Centersets look prototypical, too.

In order to install Kadee centerset type couplers, some simple modifications are required. Though Kadee plastic boxes could be used, albeit with some dimensional differences, I chose to use metal coupler boxes fitted with the couplers, springs and lid from the Kadee 907 kit.
These are the same CNC machined coupler boxes I had specially made for me by Datum Precision, Grass Valley, CA, for use on several Aristo-Craft locos - past described in another MLS thread with a much more thorough *article* hosted for me by Greg E. on his Web site. 

*Traction Tire and Wheel Size Issue*

Prior to getting the GP38, I did get two Southern Pacific USAT SD70s since they were factory made not having wheels with traction tires. So I purposely got those SD70s as my first USAT locos.

In the past, I stayed away from getting USAT locos because of the traction tires they would come with. Though, as the name suggests, the tires do afford a light weight loco to have good pulling ability, but I don't care for them because they trade-off risking electric motor damage under high load conditions that slipping wheels would tend to avoid.
Moreover, having some amount of wheel slipping minimizes axle binding forces imparted to the plastic gear collars when operating the loco on track curves. (Those collars have been reported by some folks to suffer from occasional splitting.) Also, the ability of wheels to slip lends itself for MUing to another loco having slightly different speed characteristics.
Another consideration is the diminished electrical pickup from the rails with wheels having traction tires for track power users like myself. Maybe this is a reason that USAT chose to include slider shoes to augment electrical pickup points from the rails.

Thanks to Nick Savatgy as he let me try the axle / wheel assembly shown below not having traction tires - which gave me the compelling reason to get my first USAT 4 axle loco. 
However, as to wheel size, the GP38 wheel is non prototypically small in tread diameter.










For a 1/29th scale loco, this wheel scales out to about 32 inches in diameter, whereas, the prototype GP38, GP40 and other road diesels use 40 inchers or greater. Consequently, the USAT GP38 (along with other USAT locos using the same truck) have relatively tiny wheels that would be most appropriate for a small switch engine like the GE 44 tonner!

I think the best solution is to replace the wheels with ones of the proper diameter - maybe like those supplied with the USAT SD40 that scale out to about 39 inches in tread diameter; however, this approach presents its own installation complexities - for now left to perhaps a future endeavor.

Thus, for the time being, I chose to raise the loco so that it's more prototypical for overall height from the railhead. Raising the loco is also behooving when installing Kadee centerset type couplers.

*Solutions - Raising up the GP38*

When looking up the dimensions for the GP38 versions (and GP40) in a book I have, the book drawings indicated these locos have a height "extremity" from the railhead of 15 feet, 5 inches. When I measured these model locos, the USAT GP38 was notable low whilst the Aristo GP40 was not too far off at about 6.25 inches - that scales up to 15 feet, 1 to 2 inches.









Though some folks may argue the "10 foot rule" would not make the loco look much different, but when trying to install coupler boxes with centerset couplers the height is important for how much the loco's pilots are to be notched out for the coupler boxes - as they must be to a more or less extent - with less being preferred if the loco is raised up. Moreover, if the future beholds using larger wheels instead of the spacers, the amount of notching would be very close for that application, too.

The following pictures serve to encapsulate what is involved to raise up the GP38 loco using a spacer placed between each of the truck's A frame and chassis:









The completed loco having been raised with spacers, lowered fuel tank, pilot plugs and other detail parts installed is shown.

*GP38 Pilot Modifications and Kadee Centerset Couplers*

The following pictures serve to encapsulate what is involved to modify the GP 38 pilot area, particularly with respect to installing Kadee centerset couplers:










In the case of Rock Island's GP38s, they had both snow plow and non snow plow equipped units. In this regard, as alternative to making a plug to cover the large pilot opening, USAT does offer an optional snow plow that should cover much of the opening. This snow plow (part no. R2021) is used on several other USAT locos, too, and has an MSRP of about $18.00. So if you wanted to cover both ends of the loco, it would cost twice that amount.

*Replacing an Axle / Wheel assembly* 

Shown below is what's involved when removing and replacing (R&R) an axle / wheel assembly.









With the cover off of the motor block, the slider shoes can be lifted out if you don't want to use them since they have no fasteners.

*The Coupler Mounting Pedestal*

In order to mount the Coupler box (using either Datum Precision metal or Kadee plastic), the pedestal used for the standard USAT mounted hook & loop coupler must be altered or replaced. The hook & loop coupler is shown below.










I found it easier to make a new pedestal assembly because the USAT pedestal is hollow inside, and as such, it would have to be filled with material if cut short when making it to a required less tall height.



















With the tentative height pedestal, I used a couple of stacked washers (shown below) to get the proper railhead to coupler height and leveling. Future version pedestals heights will be dimensionally better "zeroed-in" than the tentative one shown.










*Coupler Alignment* 

With the GP38 completed having been modified (raised up with Datum Precision metal coupler boxes employing Kadee 907 centerset couplers), the picture below shows coupler alignment with the Kadee 980 gauge.










*GP38 Measured Weight*

With all parts installed, the completed GP38 measured 7.9 pounds.










For much more detail, particularly for the "how to's", including loco and truck disassembly and drawings, see the *full article* hosted for me by Greg E. on his Web site. 

*Layout Operation*

Shown below is the USAT GP38 as the trailing loco with two SD70 lead units pulling a 62 car train on the under house layout. The GP38 is equipped with Kadee 907 centerset couplers installed in custom designed metal coupler boxes that I had made by Datum Precision, located in Grass Valley, CA. These coupler boxes were intended for use on many Aristo locos, so this is the first application on a USAT loco.










Shown below is an overhead view of the GP38 coupled to the first car of the train - an AML brand BN BETHGON equipped with Kadee centerset couplers. This part of the train is on the 10 foot diameter 270 degree loopback.










Shown below is an inside view on the track curve of the coupler action undergoing the train load stress 










Shown below is an outside view on the track curve of the coupler action undergoing the train load stress.










Shown below, the smooth surface clear Lexan truck spacer can be seen retained in its chassis recess. The fabricated coupler pedestal can, also, be seen.










Shown below is an overhead view of the SD70 coupled to the GP38. The SD70 is equipped with a Kadee 787 medium offset coupler adapted to a swinging box with spring return - described in *another article* hosted for me by Greg E on his Web site.










Shown below is an outside view on the track curve of the SD70 and GP38 coupled together with the stress of the train load.










*Video *

The video below (14:5 minutes) includes a description of GP38 modifications followed at 9:15 into the video by operation with the assist of 2 SD70s pulling a long train on the under house layout.

Title: *USAT GP38 Modifications & Comparisons, Including speed with the Aristo GP40 & USAT SD70*

-Ted


----------



## bnsfconductor (Jan 3, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Ted, 
NWSL makes replacement wheels (w/o traction tires) for the GP's that are the correct diameter. They come in a variety of different flange depths. The only problem is when you install the NWSL wheels you have to grind the brake pad down to get the wheels to fit correctly. 








You can see in the picture how much of the brake shoe you have to removed. Food for thought. 

Craig


----------



## Ted Doskaris (Oct 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Thank you Craig,

As to the larger more prototype GP38 wheels, I've been aware of NWSL for sometime but am not quite sure if they are still in business (or were acquired by some other company) - though their Web site appears to still be active.

The *NWSL catalog for large scale wheel sets* describes a 40 inch replacement wheel, but I am concerned that the available flange depth to be too minimal for reliable operation on a layout.

-Ted


----------



## bnsfconductor (Jan 3, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Ted, 
Let me find my paperwork I have, and get back you on the part number. The new website is kind of hard to navigate.. http://shop.osorail.com/category.sc?categoryId=87 
As long as you get the 270 wheels (thickness of wheels) you should be find with regular track work. The 270 I think is considered 'semi scale' and works with all manufactured, commercial 45mm track. DO NOT get the210 wheels as those are the 'exact scale' and they have a really shallow flange. The flange on mine (270) is ~.090". I have some where my order paperwork I can give you the exact part number...

Craig


----------



## bnsfconductor (Jan 3, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

From NWSL PDF, page 16 
/270 - the classic #1 gauge ‘scale’ tread with correct flange shape (all #1 gauge trackage) 
/236 - the semi-finescale tread (operates reliably on most #1 gauge trackage except LGB 1500 series) 
/172 - the finescale tread in 1:32 or 1:29 (exact scale wheel tread -requires custom trackage) 

Now I'm really confused, as I think I bought the 236 wheels...


----------



## Ted Doskaris (Oct 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Thank you Craig,

Can you verify the flange depth of your wheels as to which NWSL wheel version (236 or 270)?

As you likely know, I had custom stainless steel wheels made for me by Datum Precision in Grass Valley, CA for my "prime mover" type motor block Aristo locos. These wheels have a flange depth of ~0.080 inch - so

I think a depth of ~0.090 inch for a NWSL wheel will be OK on my layout, too.


Anyway, that's a project that I will try a little later on - maybe when I get another USAT 4 axle road diesel - like when RLD Hobbies finally gets the USAT GP7s in Rock Island blue livery that are way overdue.


Your info. is much appreciated and thank you again,

-Ted


----------



## Dick413 (Jan 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Thanks Ted for the post real helpful, how did you decide what was the proper projection of the end of the coupler? 
thank you again


----------



## bnsfconductor (Jan 3, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Ted, 
Here's the info from my order back in Nov 0f 2001. 
NSWL # 2529-6 
Looks like I ordered 36" wheels 270. 

Measurements: 
Wheel w/o flange 1.238" 
Wheel w/ flange 1.450" 
Wheel thickness .270" 
Flange depth ~.093" -.107. 
My wheels have been worn a little bit, so that's why I think I got a range of measurements. 

The other thing to think about too w/ the USA axles is the gear likes to split. It would be wise to fix the cracked gear now, instead of waiting for it to crack. I think Greg has info on how to do this on his website. NWSL also makes a replacement gear for the USA trains axle. The only other thing to think about is one the prototype wheel diameters are for brand new wheels. As they get flat spots, the shops cut the wheel down. So a 40" brand new wheel can get down to a 36" or smaller diameter before replacement wheels get ordered. 

Craig


----------



## Ted Doskaris (Oct 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Posted By Dick413 on 25 Mar 2012 04:18 PM 
Thanks Ted for the post real helpful, how did you decide what was the proper projection of the end of the coupler? 
thank you again 
Dick,

I emulated the Aristo GP 40 as to its molded in pilot fairing and how the coupler box was fitted. (I used the Datum Precision metal box, but a Kadee box should work on the GP38, too - though pilot notching depth and pedestal height will be somewhat different with the Kadee plastic box.)

Anyway, the coupler box projection is set at a distance of 0.400 inch as measured from the flat surface of the pilot face. 

The draft gear fairing block was made to fit on the top of the projected coupler box. Since the Datum Precision metal box is made with a lip, the fairing block was made like shown drawing.





















I hope this helps,-
Ted


----------



## Ted Doskaris (Oct 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Posted By bnsfconductor on 25 Mar 2012 06:17 PM 
Ted, 
Here's the info from my order back in Nov 0f 2001. 
NSWL # 2529-6 
Looks like I ordered 36" wheels 270. 

Measurements: 
Wheel w/o flange 1.238" 
Wheel w/ flange 1.450" 
Wheel thickness .270" 
Flange depth ~.093" -.107. 
My wheels have been worn a little bit, so that's why I think I got a range of measurements. 

The other thing to think about too w/ the USA axles is the gear likes to split. It would be wise to fix the cracked gear now, instead of waiting for it to crack. I think Greg has info on how to do this on his website. NWSL also makes a replacement gear for the USA trains axle. The only other thing to think about is one the prototype wheel diameters are for brand new wheels. As they get flat spots, the shops cut the wheel down. So a 40" brand new wheel can get down to a 36" or smaller diameter before replacement wheels get ordered. 

Craig Craig, 

Thank you for going to all effort to check on the wheels. Good data - and I am aware of Greg's Web site info. on the USAT split axle tendency as we, also, had discussed it.


The NWSL company may have changed since your order of 10+ years ago, but when I get to the point of addressing the wheels, I'll contact them. (Before I had the stainless steel wheels made by Datum Precision for the Aristo diesels, I checked with NWSL and could not get Aristo wheels at that time. They seemed to be in a disarray.


If it gets to the point of dealing with the USAT wheels and the split axles, too, it may be better to retrofit Aristo motor blocks since I have the stainless steel wheels for these already - plus I would get the benefit to run the USAT GP38 with the Aristo GP40 without conflict. I will decide later on this.


As to prototype wheel turning, taking 4 inches off the diameter off the prototype wheel seems like a bunch. I suppose the loco's electronics is such that the speed difference and traction control systems are compensated for. 


Much appreciated,

-Ted


----------



## Dick413 (Jan 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

thank you for the info.


----------



## locoguy (Jun 21, 2011)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Ted, 

I am relatively new to 1:29 scale railroading and in the (almost full-time) process of constructing an outdoor railroad with about 320+ feet of code 250 track. Would you entertain the request to modify two USA Trains GP-38 ("-2"s - per your description) with Datum Precision coupler boxes, etc., as in your on-line video. I wish, at the some point, to perform most of these modifications myself but do not have the skills or confidence to undertake this task at this time. I'm sure more skilled individuals as yourself get many similar requests but I sincerely wish to learn the craft but feel a little out of my depth at this point. I'd like to use the latest Kadee couplers and raise the locomotive to a more prototypical height, etc. 
Sincerely, 
Greg Kast


----------



## Ted Doskaris (Oct 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Greg K.,

Thank you for the flattering request, but unfortunately I do not have the time given all the other things I am doing and plan to do. For example, I've been putting off working on my extended outdoor layout for all kinds of interruptions for several years, and now I am going to resume this task with the clay ground soil now in a workable condition.

I documented all the details for the "how to's" in the *FULL ARTICLE* (link) that are not shown in this MLS thread, so why not give it a try to develop your skills? The full article that Greg Elmassian hosts for me on his Website has the same title.

-Ted


----------



## Enginear (Jul 29, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Wow, love that pilot mod. Great posting with concise directions. Have you made or bought snowplows? Are any available for other USAs? thanks, Joe


----------



## Ted Doskaris (Oct 7, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

Joe, 

I have not bought or made a snow plow.

However, USA Trains offers a diesel locomotive snow plow, part no. R2021, having an msrp of $17.50 for just one. A bit expensive. They seem to use this same snow plow on many of their other diesel products.










-Ted


----------



## Enginear (Jul 29, 2008)

*RE: USA Trains GP 38 - Mods for Kadee Centerset Couplers, Abandoning Traction Tires, Etc.*

I have the stock plow that came with my sd40-2. It fell off a couple of times. I'm not happy with the overall look of it. I would prefer a one piece plow that looked like the SFe ones. I would like to get a brass one as they usually look more realistic. Don't know of any available so I may try my first scratch build. Joe


----------



## apo234 (Aug 14, 2013)

Hey ted! I followed your article and this is what i came up with... just thought you would like to see my results





I am not done with the pilot yet... but at least it doesn't have that huge hole anymore!


----------



## Ted Doskaris (Oct 7, 2008)

apo234, ('wish I knew your real name!).

Thanks for showing your nice contribution using the Kadee coupler box. 

-Ted


----------



## Naptowneng (Jun 14, 2010)

Ted- Thanks for the great info, while I am not doing this task right now, the rebuild of the coupler pedestal is worth the read as the ones on my NW 2 have broked off several times from not very gentle coupling

Jerry


----------



## ewarhol (Mar 3, 2014)

*Ozark Miniatures*



Enginear said:


> I have the stock plow that came with my sd40-2. It fell off a couple of times. I'm not happy with the overall look of it. I would prefer a one piece plow that looked like the SFe ones. I would like to get a brass one as they usually look more realistic. Don't know of any available so I may try my first scratch build. Joe


Joe-

Check out Ozark Miniatures. They have a Santa Fe style snow plow. Not sure if it's plastic, white metal, or brass. No picture listed either.

http://www.ozarkminiatures.com/scripts/prodList.asp?idcategory=1243&curPage=2&sortField=sku


----------



## Randy Stone (Jan 2, 2008)

I find it interesting that you are concerned about the wheel diameter, yet you don't use the gauge 1 Kadee couplers.


----------



## SD90WLMT (Feb 16, 2010)

#1 couplers are awesome for scale looks..no doubt about it...

So the only credible reason for the larger G coupler is increased strength towards pulling more cars...

Dirk


----------

