SD70MAC not running full throttle

Discussion in 'HO Scale Model Trains' started by viperman, Mar 24, 2007.

  1. viperman

    viperman Active Member

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    Last night I was running my Kato SD70MAC, and it was able to only run at about 40% throttle going forward. Reverse was working fine. My Athearn RTR GP40-2 was running fine too, both forward and reverse. Any ideas?
  2. rogerw

    rogerw Active Member

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    dc or dcc?
  3. viperman

    viperman Active Member

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    oops, running DC
  4. rogerw

    rogerw Active Member

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    could something have come undone inside the engine causing it to lift up are some thing when the motor turns
  5. viperman

    viperman Active Member

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    nothing rattles inside, I checked for that. Since nothing rattles, I'm guessing everything is connected ok?
  6. Russ Bellinis

    Russ Bellinis Active Member

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    Does it have directional lighting? It could be a problem with the lighting package in the forward direction drawing too much power from the motor.
  7. viperman

    viperman Active Member

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    It does have directional lighting
  8. Russ Bellinis

    Russ Bellinis Active Member

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    I think you have a choice to either contact Kato to see if they will take it back for repair, or take it apart yourself. I think we have probably done all of the trouble shooting possible on line. Since the problem is only in one direction and only on one locomotive, the problem would appear to be internal on that locomotive and not track related. I have one more question, how many lights do you have going forward compared to running in reverse? If you have headlights, ditch lights, a mars light, and gyro lights when you run forward, but only a head light when in reverse, you may have too much lighting load for your throttle, particularly in dc. When the ho modular club used to run dc with blocks, some of the members locomotives with sophisticated lighting packages used to require twice as much throttle for half of the speed of models running without lights.
  9. viperman

    viperman Active Member

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    It has ditch lights, headlights, and running board lights, and I think maybe a light in the cab. I just find it funny that it used to run full throttle in both directions. One night I take it out of the box and it will run up to the 40% mark, then bog down. Even with no cars behind it
  10. Russ Bellinis

    Russ Bellinis Active Member

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    Do all of the lights work like they did originally? If it used to run up to speed, but now runs slow, but only in the forward direction, it sounds like an electrical problem with the directional lighting package. There is really nothing else there that isn't common to reverse direction. If it was running slow in both directions, I would suspect dried out lubrricant in the gear boxes slowing it down. I think dried, stiff lubricant would not be worse in one direction than the other.
  11. Torpedo

    Torpedo Member

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    It is posssible for reversible mechanisms to bind in one direction and run freely in the other. Worn brushes might also be the cause, if they make decent contact in one direction of rotation, but not the other.

    I would take it apart and have a look.
  12. pgandw

    pgandw Active Member

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    I would suspect that "nothing rattles" is not a good enough check of the mechanism. If it runs fine in reverse, but not in forward, there is likely a bind in the drive. Especially since it used to run well in forward. The change in performance is not likely to be electrical or electronic.

    Again, I suspect a bind in the drive that only occurs when the gearboxes and/or gear shafts shift ever so slightly when going forward. It will likely take detailed examination and running with the shell off to locate the problem - no matter whether you or somebody else does the work. If you are lucky, the source of the problem will be obvious when you take the shell off. Do you feel lucky today? :)
  13. viperman

    viperman Active Member

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    As far as I can tell, the lights still work the same they always did.

    Guess I'll have to taker apart when I get a chance one of these days
  14. Thoroughbreed

    Thoroughbreed Member

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    I betcha part of the driveline has come loose. I purchased an Athearn SD38 and when I checked it out, it did the same. I noticed it was actually dragging the non-turning truck very well, but couldnt push it. I opened it up and the drive shaft was not connected to the offending truck. Simple reconnection and problem was over.:thumb: