Problems with Atlas SD9

MP333 Nov 4, 2018

  1. MP333

    MP333 TrainBoard Supporter

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    Hey all,
    I have an older SD9, an Atlas 535xx series that came decoder ready. Installed a Digitrax way back when.

    This engine has been a real beast, very good puller although a tad noisy. Didn't bother me.

    Suddenly it has developed wheel slip, and can barely pull itself around the layout. Cleaning and rebuilding the trucks had no effect. On my test loop last night, I noticed it would occasionally jerk quickly, like a quick burst of freedom. I'm thinking a worm gear is cracked? Any ideas before I tear it all apart would be welcome.

    I've also noticed the wheels on this loco are noticeably "brassier" looking than the sister unit. They don't look worn, just a darker color.
     
  2. acptulsa

    acptulsa TrainBoard Member

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    Yes, a locomotive which moves, but only barely, and can haul no weight often has some wheels which are not turning. And yes, that can certainly be an intermittent problem. Rebuilding trucks was a good first step; I assume you made sure all the gears are meshing properly and none of them have loose bushings which allow them to slip out of place.

    A cracked worm gear is possible, and a cracked worm gear housing is more likely. Also check to see if the flywheels are tight on the motor shafts and the drive shafts and shaft/worm couplings are likewise not slipping or barely connecting.
     
  3. MK

    MK TrainBoard Member

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    What he said ^. :). I would check the dog bone and hex coupler (if it uses one) to see if there are any cracks, etc.
     
  4. John Moore

    John Moore TrainBoard Supporter

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    What I would want to examine first is the main gear in the truck which engages the worm. Normally these are press fitted on a metal shaft and depending on the plastic used may have split. A very fine crack may be observed on the gear because of it being hi lighted by oil. The crack is usually just on one half of the gear and is common on some of the older white plastic gears after time. Another source of loss of power can also be in the truck gears if they are of the split axle design and are again of white plastic. Most of the time on older locos this crack traps grease and debris which after cleaning shows as a very fine dark line. One way to check is to apply some graphite from a soft pencil lead or a dark powder such as a colored chalk or weathering powder and then clean it off and some coloring will remain in the split. A split worm gear is a rare occurrence but not out of the question especially if they are made of the white plastic. These are also press fitted on the motor drive shafts and one should not be able to turn them with ones fingers when holding on to the other end of the drive shaft. Loss of a traction tire or tires will cause this also. Atlas had two versions of these locos and since it has been awhile since I had any I cannot remember if any had traction tires.

    In case you don't have a parts diagram for it this is a link to the parts diagrams for Atlas locos.
    https://shop.atlasrr.com/t-partsdiagrams.aspx
     
  5. JBrown

    JBrown TrainBoard Member

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    Check the male universal part # 540104 in the flywheel...I bet they are cracked... they have the same common problems on the C628/630's. Order new one or try a LITTLE crazy glue on it...I mean a LITTLE...It work for me.
     
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  6. MP333

    MP333 TrainBoard Supporter

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    SP 4409 May 2018.JPG Well thank you all! I'm only a shade tree loco mechanic. But I need to dive in and see what's up. I have a small list of other Atlas spares to buy anyway, so I'll tear the thing down and get out the loupe. Thanks John Moore for the tip about graphite. I replaced the long copper wheel wipers a few years back, but they're doing their job.

    No traction tires. SP 4409 for those interested in road name.
     
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  7. tehachapifan

    tehachapifan TrainBoard Member

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    Great weathering! I also have this exact loco (SP 4409 even) and the tiny, donut-like universals that JBown mentioned cracked on mine resulting in the slipping described in the OP. I did the super glue thing mentioned earlier and that did the trick for the time being, although I also purchased some replacement universals from Atlas. I think that someone also made some replacement universals that are/were metal, but I'm not positive.
     
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  8. MP333

    MP333 TrainBoard Supporter

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    Thank you tehachapifan! It's my most extreme weathering but I love it. It hauls my cement train MU'd with 4341.
     
  9. JBrown

    JBrown TrainBoard Member

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    Briggs Models make a replacement for the C628/630's. Might work for SD7/9's.
     
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  10. tehachapifan

    tehachapifan TrainBoard Member

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    Question regarding these. Looking at the parts diagram for the C630, it appears that it has the same basic design as the Chinese SD9 where it uses the tiny donut-like male universal that attaches to the end of the flywheels. This male universal is what cracked on mine and I'm not sure if the Briggs offering replaces this particular part. It appears to replace just the universal shaft.
     
  11. JBrown

    JBrown TrainBoard Member

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    The piece press fits over the shaft where the donut was... it does work I have one. I also have just replace the donut on other with no cracking.
     
  12. JMaurer1

    JMaurer1 TrainBoard Member

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    Great weathering but you seem to be missing a few headlights...
     
  13. MP333

    MP333 TrainBoard Supporter

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    Thank you!. Yeah, we need to tell Atlas. Not my primary road, so...
     
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  14. MP333

    MP333 TrainBoard Supporter

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    Looks to be the #540104 universals are both cracked. Lost one, but no worries. Off to order parts. Oh, and there was a long carpet hair wrapped around the drive down deep, but not the main cause. I'll let you all know how this goes.
     
  15. JBrown

    JBrown TrainBoard Member

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    Looks like the part you need is out of stock right now....Tried to order some myself.
     
  16. acptulsa

    acptulsa TrainBoard Member

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    Or was it? The motor is a sufficiently irresistible force. If the end of the fiber caught on something, it could have been a sufficiently immovable object. In which case, something would have to give.
     
  17. MP333

    MP333 TrainBoard Supporter

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    Possibly. But both pieces are cracked, and one went into the cornfield. I didn't see anything about being out of stock, but we'll see.

    One thing I've always done is scan the exploded parts diagram for each model into my computer. Then it is simple to put it up on the big screen and refer to it as you go.
     
  18. JBrown

    JBrown TrainBoard Member

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    I ordered two C630 shell and the donuts and it said it would send the part when they come in. Jim
     
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  19. MP333

    MP333 TrainBoard Supporter

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    So I got the 540104 doughnuts in, put it all together, and... Nothing. Well, the motor spins but does not engage either end. I cannot figure out how to get those doughnuts onto that flywheel shaft. They seem to have a through hole too small to engage the shaft. What am I missing here? I'm using this exploded view. Atlas EMD SD9.jpg
     
  20. tehachapifan

    tehachapifan TrainBoard Member

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    Clarification...you were able to get the doughnuts on the shaft but they still slip?
     

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