Old Generation Atlas SD-35 Stalling

Hardcoaler Mar 1, 2019

  1. Hardcoaler

    Hardcoaler TrainBoard Member

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    I have an older (DC) N Scale Atlas SD-35 from 2000 acquired used that has been on a shelf a very long time. I've been running it tonight and it intermittently stalls on perfect straight track and elsewhere. I've messed around with a ohmeter and I think the problem is the contact strips between the chassis and the trucks are making unreliable contact. I've bent the contact strips so that they apply more pressure to the truck contacts and it's helped. (The newest gen of Atlas SD-35s finds the trucks hardwired to the frame.) Then other times I think that the trucks aren't doing a good job picking up current.

    If I wanted to open the trucks and clean them, how do I get them apart? I can't see how to unsnap them.

    I've checked the motor contacts to be sure they're making good contact on the analog circuit board.

    Is there a known "bad actor" that's often the culprit with this design? I don't blame Atlas, as this unit has probably sat for many years. Thanks y'all!
     
  2. Point353

    Point353 TrainBoard Member

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    I'd disassemble the trucks only as a last resort.
    Before attempting that, clean the tops of the contact tabs on the trucks and the bottom sides of the contact strips.
    Also, clean the contact strips on the motor and the spots on the frame that they touch.
    Use a plastic-safe contact cleaner such as this one from CRC: https://www.crcindustries.com/products/qd-174-contact-cleaner-11-wt-oz-02130.html
    Don't spray it straight from the can directly onto the model.
    Spray it into a small container first and then use a cotton swab or paper towel to apply it.
    Cleaning the wheel treads by moistening a section of rails with contact cleaner and running the loco over it wouldn't hurt, either.
     
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  3. randgust

    randgust TrainBoard Member

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    You also may have some 'crud' built up inside the end-axle contacts. While you can disassemble the trucks and hand-clean those, that's one of those 'well, nothing else worked' options. I do recommend that you get something like Atlas Conductalube, it's done wonders for my end-axle contacts, I've done tests before and after, and it really does work and slow down re-oxidation. If a locomotive is heavy enough, it will self-polish those contacts, but I've seen Atlas locomotives that still managed to get those corroded up pretty bad in there if they sat long enough. I had a GP7 that was normally a stellar performer, sat for about six months, and would hardly run at all - conductalube in the end-axles fixed it instantly without any disassembly needed.

    Another big helper is just to have a set of jumper wires with tiny alligator clips on them so you can literally hotwire around spots when a locomotive stalls. You can clip to the rail, then start probing toward the motor, and see at what point it restarts. That will identify just what component is the problem, all the way up from wheel treads to the motor itself.
     
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  4. Hardcoaler

    Hardcoaler TrainBoard Member

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    Thank you both. Using the jumper wire/alligator clip technique I think I've found that one side of one of the trucks is not contacting reliably. I have a can of Point's CRC QD Contact Cleaner, but it was tough to apply it by hand within the truck recesses. I'd rather avoid dismantling the truck, but it may be the only way.

    I just found an excellent video by Mike Fifer that shows how to dismantle a Kato truck and hopefully it'll work for Atlas. The locomotive that Mike dismantles shows axle end caps on the truck's contact strips that are black with crud and that might well be the case with my old SD-35.
     
  5. Point353

    Point353 TrainBoard Member

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    In that case, as randgust suggested, get a bottle of the Atlas Conducta Lube Cleaner.
    It comes with a needle applicator which you can use to drip some of the lube onto the axles between the front face of the wheels and the inside of the truck frames.
    If that method works it will save you the effort of taking the trucks apart.
     
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  6. WM183

    WM183 TrainBoard Member

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    The trucks are a puzzle box, but not a terrible one. Don't worry too much!
     
  7. urodoji

    urodoji TrainBoard Member

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    Don’t overlook the contact between the motor and PC board.
     
  8. Tony Burzio

    Tony Burzio TrainBoard Supporter

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    The biggest problem is the desire to pull the trucks out without removing the chassis screw. Bad juju. Another is holding the engine down too hard when spin cleaning on alcohol paper. This tends to mess up the gear tower.
     
  9. Hardcoaler

    Hardcoaler TrainBoard Member

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    Success! With no options left on my used Atlas SD-35, I pulled the sideframes free of the suspect truck mechanism with surprising ease. The axle-end contract strips on both sides fell out, causing me some alarm. Happily, the axles do not fall out when the sideframe is removed.

    One of the axle contact strips had pockets of black schmutz in all three indents and this one strip was somewhat discolored on the inside too. I used CRC QD Contact Cleaner and a cotton swab to clean out the pockets and the axle ends. I wasn't able to brighten the discoloration to make it look bright like its mate. Using a jeweler's loupe, I also found tiny fibers wound around the axles and spent quite some time plucking and pulling these out.

    I also found that the wheels were out of gauge, some wide and some narrow. Using my NMRA gauge, these were set and the truck was reassembled.

    I didn't mess with the other truck, as its handling its duties well and all three axles are in gauge. Why look for trouble, right? :oops:

    I've had the unit running at slow speed in both directions on my test oval for 30 Minutes now with no hint of stalling. Yay! Thanks again for everyone's help with this.
     
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  10. MK

    MK TrainBoard Member

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    Good to hear that! It's usually crud in those dimple pockets when all else fails
     
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  11. Tony Burzio

    Tony Burzio TrainBoard Supporter

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    After a couple ten thousand real miles, about ten years of daily use, those metal dimples in the bearing frames will wear through. I would not have believed it if I hadn’t seen it myself! Of course, most Seksui engines (Kato before it was labeled Kato) will never see the kind of extreme punishment like at the SDSoNS in San Diego... :)
     
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  12. randgust

    randgust TrainBoard Member

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    Once you get the jumper-wire thing going, life gets easier. You aren't tearing stuff apart randomly or guessing. You'll find out real fast, like you did, it was one side of one truck.

    I also have an Atlas C80 #6 mainline two-track crossover on my ATSF layout, part of it shows on my signature page photo. That has a LONG insulated plastic frog, longer than most trucks, on both switches. Any given locomotive stepping through that is subjected to each truck being completely 'shut off' on one side, and then the other, as it runs through. If either truck, or either side, isn't working 100%, dead stall. That's the only quicker way to find out if you've got a dead set of pickups on a truck and identify which one and which side.
     
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