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Problem with Athearn ready to run SD40 Locomotives

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  • Member since
    December, 2008
  • 6 posts
Problem with Athearn ready to run SD40 Locomotives
Posted by nitro FC on Wednesday, December 17, 2008 1:28 AM

I previously posted this message on the general discussions forum. It may have been the wrong forum to post it, so I thought I'd try it here. Hopefully, somebody has a solution, other than sending the locomotives back to Athearn. They will (more than likely) just send me new ones, that probably will have the same problems.


We have two of these locomotives. They both have the exact same problem. Both have plenty of front to back axial motion in their trucks to allow them to traverse minor deviation (bumps) in the track. Neither has any side to side axial motion. This causes them to derail on any section of the layout that has even the smallest side to side deviations (level mismatches, etc). It also causes them to 'pick' switches more often. None of our other locomotives (nearly 150) have these derailment problems, only these two. All the rest of our locomotives (all are HO) have plenty of  front to back axial truck movement and plenty of side to side axial truck movement. We can send them back to Athearn, but they will jus replace them with the same locomotives, without fixing the problems. As the problem exists in two SD40's, we are guessing it is a 'model problem' affecting only the SD40's. Is there a fix? The locomotives, other than this problem, run great.

Thank you

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Posted by dstarr on Wednesday, December 17, 2008 8:46 AM

Do all of the above first.   If memory serves the SD-40 is a 6 axle locomotive, and from your posting I assume that you want some side-to-side play in the middle axle to ease the locomotive around curves.  What radius are your curves?  18" radius is tight for 6 axle engines.  Make sure your curves are not tighter than 18 inches (Flextrack can be bent very sharply) and sight along the track for kinks at the track joints. A big 6 axle locomotive will require the best possible trackwork.

Then if you are feeling mechanically inclined, take the locomotive apart.  Assuming the SD-40 is similar to my lesser Athearns, (GP38 & F7) the shell is retained by clips and will come clean off after you tease the lugs on the clips out thru the mounting slots.  The gear towers on the tracks are held closed by a snappy clip in the bottom.  An Xacto knife will pop the clips off and then the trucks/gear towers come apart.  The truck sideframes are a press fit into the metal "core" of the truck and can be pried off.  Be careful not to twist and break the mounting lugs cast into the backs of the sideframes.  

   Once apart inspect for flash and bits of crud left in the works.  If you wipe each tooth of each gear with a pipe cleaner you will likely find a few small nearly invisible fragments of black plastic on the white pipe cleaner.  The gear sets will run more quietly after cleaning.  

   Once apart, you ought to be able to get a bit more side-to-side clearance on the middle axle by filing something, the back of the wheels, the truck or bearing.  


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Posted by jeffrey-wimberly on Wednesday, December 17, 2008 9:11 AM

 Any replacement will have the same problem also. I have one of the rtr SD40's myself and it has the same thing with the tight trucks. A solution on mine was to pop the front worm housing loose a little. This enables the front truck to rock side to side a little and it no longer derails. I never had a problem with it picking turnouts. Removing the shell from this model is quite simple. Remove the screws holding the coupler boxes in place and pull the coupler boxes out. The shell will come right off.

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Posted by BRAKIE on Wednesday, December 17, 2008 9:11 AM

I had a BB GP7 that would do that..I found the wheels was not in gauage-to wide..Once the wheels was properly gauge the engine ran and still runs fine.




“Shut one’s eyes tight or open one’s arms wide, either way, one’s a fool.” Flemeth-the witch of the Wilds.
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  • From: Buellton,CA.
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Posted by cliffsrr on Wednesday, December 17, 2008 9:13 AM

I also was having this problem with six axle trucks, The problem was my poor track laying which four axle trucks handle well. In desperation I removed the middle axle/wheel flange and turned the diameter down a few thousands. The middle wheel is not really that visable and you don't notice the change if you are not looking very close.

Lots of luck


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  • From: Holly, MI
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Posted by ClinchValleySD40 on Wednesday, December 17, 2008 10:39 AM

I have the same issue with some Athearn SD38's.    Try this after doing the checklist if you still have a problem.   Turn it over and remove the center axle.    All wheels are 40" and I've found substituting 42" on the outboard two axles (leaving the 40" in the center) solves the problem.   I'd do the remove center axle check first to see if the problem goes away before ordering new wheels.



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Posted by nitro FC on Friday, December 19, 2008 11:45 AM

Thanks for the input.

The wheels are in gage (checked withNMRA gage tool) and there are no curves on the layout less than about 30 inch radius. Took the worm gear covers off the locomotives. I then filed down the raise section of the frames slightly and filed the pointed end of each worm gear cover. this provided the side to side (up and down) motion needed. This cured the problem. Also did some minor repairs on the layout track. At some spots in the curves (especially near rail joiner sections) the guage became very slightly pinched. For whatever reason, the very slight pinch in conjunction with the lack of (zero) side to side up and down movement of the trucks, would cause only these locomoitves to derail.

Of intrerest to note, we also have a set of Ahtearn ready to run SP daylight heavy passenger cars. These cars have adificult time passing through any curves, even when the track is in guage (as tested with an NMRA track guage tester. As stated earlier, there are no curves less than 30 inches of radius. Most are 34+. The problem with these cars is in the three axle trucks. If yo take the middle wheels of each truck,  the derailment problems go away. It appears that we are going to need to de-flange the middle wheelsets on each truck for each car. Hopefully, we can find some 'flangeless metal wheels' for these cars, without having to go tothe use of plastic middle wheel that we file off the flanges on. As everyone knows, metal wheels are preferred over plastic as plastic wheels tend to collect dirt.

 It also appears that we will need to have the middle wheel flanges removed from our Bachman GS4 locomotives, as they suffer sporatic derailments because these locmotives have very little 'forgiveness suspensions'. They do like like turnouts, but will run pretty good through the hand built 'fast track' turnouts we have on the layout.

No need to de-spur the gears as all the locomotives run smooth and quiet (no gear knock or related noise).


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Posted by FWDman on Saturday, December 20, 2008 12:47 AM

This is nothing new. The Green Bay and Western only used B-B diesels due to tracking problems on their line.


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Posted by nitro FC on Monday, December 22, 2008 11:48 PM

You would lose money on this deal. The wheels have all been guaged with an NMRA tool. The track curve radius in the sections in question are not less than 34 inch radius (as measured with a 'ribbon rail' curve track radius tool and checked with an NMRA guage tool). Other sections on the layout, where these cars are run, are not less than 30 inch radius (as measured with the 'ribbon rail' curve track laying radius tool and checked with an NMRA guage tool). We do have sections on the layout (the cars are not normally run in these sections) that get down to about 22-24 inch radius (a couple of industrial access sidings; these are  'heavy weight' passenger cars).

 The questionable sections of track are flat. When I roll the car(s) through by hand (one car at a time or several coupled together), resistance can be felt. The flanges on the wheels themselves have become 'polished', such that I can see where the flanges are hitting the rail. Not every wheel on the cars have this problem. Upon close scrutiny, I found that even though each wheelset is 'perfectly in guage' (as check with an NMRA guage tool; we have two of these for HO, so I tried  both tools), the actual wheelsets (three per truck) do line up properly. As only one wheel per axle can be moved on the axle the other one is pressed on very tightly), I am unable to get all three wheels on each truck line up the same on the track rails (even though all the wheels are engage). i will probably resort to grinding the flanges off the middle wheels of each truck, as the cars run perfectly fine through all sections of track on the layout with the middle wheels on each truck removed. By removing the flanges on the middle wheels on each three axle truck, I should be able to keep the middle wheels on (with the same diameter, thus not effecting the over-all appearance in any way) and eliminate the flange binding caused by these middle wheels. I could buy all new wheels, but the cost for metal wheels is a couple steps shy of ridiculous ($9.95 per pack; and there is no guarentee that will fix the problem). If they manufactured flangeless metal wheelsets, I'd buy some.

 Other than these cars (Athearn ready to roll), all of are rolling stock that we use (over 150 pieces) have metal wheels (Proto or Intermountain). Even with those wheel sets, we've had individual cars with derailment problems (even though their wheel sets check out 'in guage'). Sometimes we've from track problems or had to do major modifications to the track to take care of the couple affected cars. Often we found it was just the cars. Most of our cars have all been weighted to NMRA standards. These passenger cars are a little 'lighter' than NMRA recomendations, but adding weight will only make the cars heavier (I did temporarily add a bunch of weight to one of the 'problem cars'; it quit derailing as much, but bound up more on the curves, so I took the added weight back out - all the passenger cars we have of this type do not have this derailing problem, though all of them bind on the flanges somewhat), thus over loading the GS4 locomotive with less cars attached. Adding weight has seldom (if ever) corrected these types of problems (only lessoned the number of cars you can place in a train). We have quite a few cars (rolling stock) weighing in at about 1/2 to 3/4 of the "NMRA recomended weight" that run around the entire layout without one single problem. They vary from Accurail, older Athearn rolling stock, 2-axle to 3-axle truck, Intermountain, Proto, Branchline, Athearn 'ready to roll'  and others (kit cars and ready to roll cars). All rolling stock used on the layout has also been coupler guaged with a Kadee couple guage and the trip pins shortened so they do not bind with the other coupled cars trip pin, nor do the trip pins hit any part of the track work.

The only problem track work, that we currently have, is a spot where the track level changes too abruptly (bump). This has not caused any derailments (it is located in a straight section), but has caused some minor uncoupling problems with the trains. We are in the process of fixing this problem area in the track.

It does appear that I am not the only one with this type of problem. The weighing of the rolling stock (and locomotives) is in no way prototypical. A GE 4400 AC (real life) weighs in at about 400,000 lbs. If you divide that by 87 (1/87th scale is HO), our locomotives would need to weigh in at about 46,000 lbs! This obviously cannot be done! Thus the 'real locomotives' can negotiate track that is more out of shape (proportionally speaking) than our HO stuff. I've photographed and looked very closely at prototypical track (sidings, mainlines, etc) and found them to be far from perfect. We only the best out of what we have. Unfortunately, we cannot get the added weight to stay low enough so as to not make the items 'top heavy' (especially rolling stock). It would be nice if someone could produce heavier wheelsets that looked good and were affordable (two things that definately do not go together in this hobby).

In reference to the Athearn 'ready to run' SD40's, I used the one of the inputs, given in an earlier post. I filed down the section where the worm gear cover clamped to the frame. This provided the necessary 'side to side' axial motion to correct the derailment problems with both of these SD40 locomotives. Both now run around the entire layout (eveywhere, any siding, spur, etc) with no problems (at any speed from prototypical to 'Lionel High Balling').

I must thank those who contributed the ideas that corrected the problem.

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Posted by Artur on Tuesday, December 23, 2008 12:31 AM

That is an incorrect calculation, mass is based on a 3 dimensional volume. Here is the correct calculation for a 400,000lbs locomotive

400,000lbs / 87^3 x 16 = 9.72 oz

The model in HO (1:87 scale) should weigh 9.72 oz

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Posted by maxman on Tuesday, December 23, 2008 12:38 AM

If the track radii are as you say, I would go out on a limb and say that there is absolutely no reason for you to need to be grinding off the flanges on the middle axle of any piece of equipment on your railroad.  This just does not sound right to me.  Maybe others will agree.  I think something else is wrong.

You mentioned that there are sections of track where you feel resistance when you roll a car through.  Are these areas where the track has been nailed down?  If so, is it possible that the nail head has buckled the tie down in the middle causing the rail gage to narrow?

I think I understood your description concerning not being able to get the SD-40 wheels in line, but I'm not sure why not.  Are not the wheelsets actually half-axles pushed into a center gear?  If so, you should be able to pull either wheel in or out as required to get things in line.

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Posted by cwclark on Tuesday, December 30, 2008 3:16 PM

I have the same exact problem with the Athearn RTR SD-40 and found that one of the gears on the wheels is not true and needs replacing. You are the 3rd person i've heard complain about this particular model. What i did was go thru a box of old athearn parts and started replacing the wheel sets one at a time with wheels from other old athearn locomotives that bit the dust years ago.. i finally found that the third wheel on the front truck was wobbling badly and on inspection, found that the gear and the wheel axle are not aligned properly (factory defect.) It runs great now with the new (old) wheel from an old GP9 that went south on me a few years back.

     I wish Athearn put a little bit more emphasis into their quality control. It took me 2 days to figure out what was wrong with the SD-40. I ground the axles as mentioned, checked for the trucks hitting the frame, and gauged them twice before finding the real problem with the wheel, axle, and gear assembly...chuck

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Posted by Harpo1me on Friday, January 11, 2019 3:32 PM

The problem with the 6 AXLE RTR truck is the side play is too tight. Replace the oversized fat axle bearings with standard blue box axle bearings and problem solved. The axle spacing is the same as a sd40-2 truck and a blue box dash 9, but for some reaso Athearn changed the axle bearings to a fatter bearing that causes the problem. Found this on accident doing a refurbish and had a few rtr axles thinking they were the same as the blue box axles and mixed them up .Encountered running issues on a rebuild and found the fat bearings from rtr that do not work well in a blue box truck either. Hope this helps. Dont use different size wheels that is just backyard wrong


Any replacement will have the same problem also. I have one of the rtr SD40's myself and it has the same thing with the tight trucks. A solution on mine was to pop the front worm housing loose a little. This enables the front truck to rock side to side a little and it no longer derails. I never had a problem with it picking turnouts. Removing the shell from this model is quite simple. Remove the screws holding the coupler boxes in place and pull the coupler boxes out. The shell will come right off.

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