AML Pullman Standard 4750 ft3 Covered Hopper Fixes & Kadee Body Mount Couplers

AML Pullman Standard 4750 ft3 Covered Hopper Fixes & Kadee Body Mount Couplers
Ted Doskaris
October 31, 2011
Rev GE-A

December 25, 2011
Rev GE-B:  added dimensional drawings - including definitive "S" Bend Clip  dimensions; added MKT car example material; added video

March 26, 2013

Rev GE-C  added Appendix A: Accommodating a Car having a Twisted Coupler Pad

August 3, 2014
Rev GE-D  added Appendix B: Weight added to the car for outdoor use

December 15, 2017
Rev GE-D1  Repaired broken link

September 27, 2020
Rev GE-E  added table of contents; added Appendix C: Available 3-D Printed "CamPac" coupler boxes & "S" clip for anchoring chassis mounting pad to car end sill.

The car shown below is equipped with direct fit (no spacer) small foot print CamPac BoxesTM fitted with Kadee centerset couplers





Problem Issues
Re-inforcing / Repair Method Done to the Car's Under Frame
Installing Kadee 906 Centerset Coupler Assemblies
Lubricating the Car's Axles
Operation On the Layout
Appendix A, Accommodating a Car having a Twisted Coupler Pad
Appendix B, Adding Weight
Appendix C, Alternative 3-D Printed Coupler Boxes & "S" Clips
Where to get CamPac Boxes & Clips



I now have several AML PS2 4750 cars as of this writing date that include one each, Frisco, MKT, Santa Fe and two Rock Island. Discussed are MKT and FRISCO example cars.

The Frisco car is shown below.

The American Main Line (AML) Pullman Standard (PS2) 4750 car's roof hatches can be opened, but care should be taken when closing them so that they are fully seated.

There are two sliding hopper dump doors per bay on the under belly of the car.  The picture below shows the doors open - exposing a screw for attaching the under frame spine.

The AML PS covered hopper car is a well detailed and crafted car with absolutely beautifully made all metal roller bearing type trucks (plastic bearing caps & brake shoes, excepted) having the nicest finished metal wheels I have seen to date.


Note the factory truck mounted coupler is on a metal bracket that is fastened to the truck's bolster with two small screws.  Only the AML factory coupler is plastic here.  These parts are to be removed when using body mount couplers.

The wheels are superb and roll smoothly on the track rails.  They appear to plated, and a magnet is attracted to them.

One issue noticed with the trucks was a squeaking noise that sometimes occurs when the car was operated on a curve track as the axles tend to skew opposite from one-another.  The noise is caused by the plastic brake shoe being marginally close to the wheel flange during this circumstance.  In this regard, I have determined different ways to fix this that is the subject of another vignette (article); see  "Optimizing the AML Metal Roller Bearing Truck", also, hosted on Greg's. Web site.



Problem Issues

The SLSF (aka Frisco) and MKT cars I purchased and received both suffered damage in the way of a detached under frame assembly (at both ends of the car) located below the bolster where trucks mount.  The under frame spine relies on factory gluing to the car's upper body at the bulkheads above the truck pivot area without any mechanical fastening.  Given this inherently fragile fastening method, it's possible shipping damage occurred due to vibration during transport from the China factory, not just during local delivery from the retailer.


The MKT car shown below suffered damage like the Frisco car.

The failure of the factory glue joint can be seen in the above picture.  Note the blistered paint along the seam area where the glue only seems to have dissolved the paint while not effecting a bond.

With the weight of the metal truck assemblies (about a half pound each) dangling at the ends of the under frame, the cars I took out of the boxes was unusable. 

The Frisco car, also, had a dangling part, that was easily fastened with CA glue.  (This was a common problem with the USA Trains brand Cylindrical Hopper car, too.)

Another thing on a car to check are the positions of sliding doors on the under belly of the car.  These doors and the detail parts that secure them may have assumed unintended positions during shipping.

Since these are relatively expensive freight cars, it was a bit disconcerting to have received them in such a damaged condition.  That said, I was able to not only fix it, but make it stronger than the factory before it had been damaged.  Along with the repairs, Kadee 906 centerset coupler assemblies were, also, installed.


Note: As an alternative to using the relatively large Kadee 906 or predecessor 830 box assemblies, smaller foot print, direct fit (no spacer), 3-D printed boxes and "S Clips", that aid in preventing chassis under frame separation, have been developed. These are described in Appendix C.

Re-inforcing / Repair Method Done to the Car's Under Frame

Step 1, Re-bonding the under frame:

The under frame can be re-bonded to the car body bulkheads by applying a bead of CA type glue.  This is best done with the car placed on its side and then holding the glue bottle whilst approaching the narrow bulkhead ridge surface as shown in the below picture. 

Doing the gluing the way shown above seemed to limit any glue spillage to the inboard area that won't be readily seen and would be less noticeably touched up with paint that may not have a perfect match to the car's livery.

Step 2, Reinforcing the bonded area:

Since the surface area of the bonded joint is very thin, it's possible (given the weight of the metal trucks) that there will be a tendency to stress the bond when lifting the car, inviting separation once again.
I used a small 3/32 inch thick ABS plastic strip, 1/4 inch wide by 4 inch long (notched to clear the under frame spine) that is CA glued in place such that it spans the joint area.

That said, using a clip to anchor the chassis coupler mounting pad to the car's end sill also can aid in preventing separation - described in next Step 3.

See the following  dimensional drawing and pictures:

The re-inforcing strip is to be placed over  the bonding joint - to be CA glued on.

The plastic strip, having been CA glued down, spans the bonding joint -  thereby, reinforcing it.

The plastic reinforcing strip can be prepainted prior to gluing it in place like that of the example MKT green car livery as shown below.   Painting the strip to match is surrounds and a placing it on the inboard side of the bulkhead makes it less obvious that it's there.

Step 3, Mechanically supporting  coupler mounting pads to car ends:

The under frame coupler mounting pads have a predisposed downward tilt that can be corrected by using a small "S" clip fabricated from metal to hold the pads up against the car ends.

A dimensional drawing of the "S" Bend clip is shown below.

I found using the plastic block very desirable for consistency and CA glued it on the clip - then took  the 2-56 tap to chase the threads of both clip and block.

If the "S" bend clip were made too long it can't be used because it will result in too low of a coupler height to track, but if it is made just a bit too short it  can fixed and  be used as shown below.


Mechanically attaching the cantilevered under frame pad used for body mounting couplers to the end of the car will help prevent the previously described glue bond from separating.  It will, also,  establish a stable and more consistent pad attitude beneficial for installation and operational use of body mount coupler assemblies.

The "S" bend clip can be pre painted, making it less obvious.


The "S" bend clip installation was done in conjunction with the Kadee 906 coupler assembly installation; however, this can and should be done if body mounting AML coupler assemblies - or even when using truck mounted couplers.

Installing Kadee 906 Centerset Coupler Assemblies

The Kadee 906 coupler boxes must be trimmed on the sides so as to allow car operation on curve track such that the wheels don't rub when the trucks pivot.  This should be done so operation will work on  8 to 10 foot diameter curve track.

Illustrated below is a method used for trimming the Kadee 906 coupler boxes

The Kadee 906 boxes are mounted using the center holes.  The front screw also serves to mount the "S" bend supporting clip previously described.

A pin vise can be used to drill the corresponding coupler box in line center hole, then it is to be tapped for a no. 2-56 screw.

Shown below is the Kadee 906 coupler box  mounted using only the center holes.  When mounting the coupler box with the front screw, position the "S" bend clip opposite the front hole directly underneath the pad whilst fastening the screw.  The front screw will retain both the coupler box and the clip.

When installing the "S" bend clip, first ensure the front mounting screw in the coupler box does not protrude beyond the pad surface so the clip can be held flat against it.  Pre positioning the clip and then pinching it together with the coupler box so the clip is flat against the pad should be done, then the screw can be threaded all the way in - otherwise there will be an air gap between the clip and pad, resulting in an improper coupler to track height.

I found some wheel rubbing on the coupler boxes when operating the car on 8 foot diameter track curves.  10 foot curves had no restrictions.  With more material removed than shown in prior pictures, 8 foot curve operation could be further improved.

Shown below is proper coupler alignment with the Kadee 980 track height gauge.


Lubricating the Car's Axles

The car as it came out of the box rolled freely enough; however, upon close inspection it was difficult to see if any lubricant was present, so I chose to apply automotive Molly Paste to the axle hub areas. 

As shown in the picture below, to provide a bit more room to get into the tight space, the plastic roller caps can be pried off the axle tips, and the springs can be temporarily removed from one side frame - allowing the frame to be dropped down and slightly pulled outward.

With trucks installed and all the work done on the car, it measured 3.10 pounds, which is fairly light for such a large car, but heavy enough for good operation in a long, heavy train when on the layout's more critical curves.


Operation On the Layout

The AML PS2 4750 Frisco Hopper car was placed behind the trailing loco on a 62 car test train.

Shown is the train rounding the 10 foot diameter, 270 degree loop back.  This is a good area to stress test the car's performance with its body mounted Kadee 906 centerset coupler assemblies.

Shown below is an overhead view of the car's coupler loading on the 62 car train.

Shown below is a close up, inside view of the car's coupler loading on the 62 car train.

The lip of the "S" bend support clip can be seen straddling the car's sill in the below picture.

The optional black plastic support block can be seen on the clip in the below picture.

Shown below is a close up, outside view of the car's coupler loading on the 62 car train.

The other end of the car is coupled to a USA Trains brand cylindrical, 4 bay hopper car; the support clip's lip can be better seen in the below pictures.

Shown below is the coupler inside view of the AML PS 4750 hopper car on the right with the USAT ACF cylindrical hopper car on the left.

Shown below is the coupler outside view of the AML PS 4750 hopper car on the left with the USAT ACF cylindrical hopper car on the right.

Shown below is the coupler overhead view of the AML PS 4750 hopper car on the right with the USAT ACF cylindrical hopper car on the left.





An 8 to 9  minute video (selectable for 720P) showing the AML car operation in the long, heavy 62 car train on my under house layout may be helpful  to look at:
Title: AML PS2 4750ft3 Hopper Car with Fixes & Kadee 906 Body Mount Couplers on 62 Car Train


With slight modifications done to the AML PS2 4750 covered hopper car to improve its under frame glue joint durability and to accept Kadee 906 centerset type coupler assemblies, the car performed flawlessly while operating  in a 62 car test train (coupled to and being pulled by 3 Aristo-Craft GP40 locos) on the under house layout.



Appendix A, Accommodating a Car having a Twisted Coupler Pad

A more recent acquisition is the Santa Fe PS2 4750ft3 Hopper car shown below.

This Santa Fe car seems to have survived the worst rigors of shipping damage compared to prior cars in that it did not have its under frame broken away from the upper body - a good thing.

Unfortunately, as shown below, this car did suffer from some minor shipping damage - repaired by reattaching with CA glue.

However, of more concern was the defect in one of the coupler pads - shown above. Note the pronounced twist in the coupler pad. This warped coupler pad cannot be attributed to shipping damage, but perhaps the result borne from the factory's timing of the molding process. Quality control inspection seems to have overlooked this!

For folks using truck mount couplers, this would be of an aesthetic issue; however, when using body mount couplers, this presents a problem. Attempting to fix it by trying to twist it back straight would not work since it's too thick and would stress the rest of the under frame. It's possible applying heat whilst twisting it straight may work, but with much risk of inflicting damage unless one develops a skill before hand; however having to resort to such methods, it would seem better to just return the car under warranty claim.

That said, a Kadee 906 coupler assembly can still be mounted on the warped pad by building up the front corner with aesthetics minimally noticed.

Shown below is the mounted Kadee 906 centerset coupler assembly. Note the box was trimmed on its sides as shown so the truck is allowed to pivot a greater amount. This allows car operation on tighter track curves of 8 to 10 foot diameter - otherwise the wheel will bind up against the box.

Note the brass "U" shape insert in the truck bolster is for the purpose of keeping the side frames parallel. It acts as a spreader spring. Using this device will prevent the wheel flanges from coming into contact with the brake shoes which can happen on curves. It prevents wheels from making squeaking noises and needless drag - which is an issue for all AML cars that used this truck type. For detail information, see article, "Optimizing the AML Metal Roller Bearing Truck", also, hosted on Greg's. Web site.

Shown below is a side view of the mounted Kadee 906 centerset coupler assembly in alignment with the Kadee 980 gauge.

Shown below is the car (warped coupler pad end) on an 8 foot diameter curve track.

Shown below is the other end of the car (brake wheel end) on the same 8 foot diameter curve track.

Shown below are the car and locomotive uncoupled over a Kadee magnet.



Appendix B, Adding Weight

While the AML PS2 car operated OK on my under house layout, when outdoors a gust of wind would tend to blow the car off the track! This car is relatively light for its size and length, weighing at 3.1 pounds, and it's top heavy. The solution is to add some weight in the lowest part of the car, which is in the hopper dump area.

Additional weight can be added to the AML PS2 hopper car through the top hatch openings.

I added a total of 1.5 pounds, comprising two weights 3/4 pounds each, in the center hopper on either side of the spine. The spine is the rib that runs the length of the car which can be seen within the car from the top opening. It divides the hopper dump area.

From the outside of the car, the spine can be seen running the length of the car, passing through each hopper bay.

I used no. 9 lead shot purchased from a firearms store placed in small plastic "bladder" bags.

The bladder bag can be squeezed so it fits through the top opening of the car.

The excess pigtail of the bag is then cut off before the bag is dropped in place.

Using a wood stick, the bladder bag is positioned into the hopper crevice (one bag on each side of the spine).

Using the wood stick to push down on the bag, the bag can be made to somewhat conform to the shape of the hopper.

Both bladder bags now in place are shown below

After the bladder bags are installed they are to be retained so the car can be turned upside down without dislodging them. This can be done using packing material - gradually poking it through the slot.

Gradually install sufficient packing material until it snugly fits up to the top of the two slot openings above the car's center bay area.

When done, close the hatches.

With the added collective weight of the two bladder bags comprising 1.5 pounds, the car's total weight now measures 4 pound, 10 ounces.

With the added weight placed down low in the car, its affect is to stabilize the car, preventing it from being blown off the track should the force of a gust of wind strike the slab side of what had been a top heavy car.



Appendix C, Alternative 3-D Printed Coupler Boxes & "S" Clips

The same Frisco car that had the Kadee 906 box will now be used to illustrate the 3-D printed box choice.

Rather than trimming the large Kadee 830/906 box and fabricating a metal bracket to anchor the car's chassis to its end sill, 3-D printed parts are available to make for a more user friendly experience. Moreover, the small foot print CamPac coupler box (also body mounted) allows the car to operate down to 8 foot diameter track curves without being concerned with wheels rubbing - that must be mitigated by trimming the comparatively large Kadee box.

CamPac parts include the small foot print coupler box and "S Clip" that anchors the chassis pad to the end sill of the car. End sill anchoring is needed so the mounted couplers can align with the Kadee coupler height gauge, and the clip also serves to help prevent the chassis from separating from the body shell as previously described. The CamPac BoxTM accepts all parts from the Kadee 906 kit, except of course the Kadee box itself, and the Kadee screw that attaches the lid must not be used, otherwise damage can result.

The 3-D printed "S Clip" is illustrated below - albeit appearing much larger than it really is.

The relation ship of the "S Clip" and box can be seen below.

To be sandwiched between the Clip on the top and Box on the bottom will be the chassis mounting pad. This can be seen in the following illustration.

In the above picture, note how the Clip's lips tucks below and above the car's end sill to lock the chassis in place.

The "S Clip " serves three roles:
(1) It anchors the chassis coupler box mounting pad to the end sill of the car, thereby, aiding in the prevention of chassis separation from the body shell in the vicinity where the trucks mount
(2) It's used as a nut plate to fasten the CamPac BoxTM fitted with Kadee centerset couplers
(3) It facilitates aligning the couplers with the Kadee coupler height gauge

This is graphically shown in the following illustration:


Mounting the CamPac Box:

Note: Also available is an Installation Guide published on Colin Camarillo's website where 3-D printed parts can be obtained.

Like done for the larger Kadee 906 box & fabricated clip, the chassis mounting pad needs the added hole in the same place, but for having clearance of the #2-56 screw to pass through.

The CamPac BoxTM can be used as a template to locate and drill the hole.

A method for installing the box & clip is illustrated below:

The mounted box is shown below.

With the truck rotated at its extreme, there is more wheel clearance than the larger Kadee 830/906 coupler box, so car operation down to 8 foot (and slightly tighter) diameter curve track is without wheels rubbing.



Where to get CamPac Boxes & Clips


If interested in obtaining 3-D printed boxes designed by me (Ted Doskaris) and implemented by Colin Camarillo on a 3-D printer, visit Colin Camarillo's website.




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