Model Railroading > Sluggish Athearn SD50

Hi all -
I have an Athearn SD50 I am trying to speed match, and I'm finding that this unit just doesn't like to get started.  The motor starts at speed step 1, but it's unable to get the gearboxes to get going until speed step 25.  I disassembled and lubed the trucks (with WD40, that's all I had on hand) and I didn't see any obvious problems... the trucks would only free-wheel maybe 6-8 inches before lube, and maybe 10-12 after.  But no real improvement in performance after that.

It's been awhile since I messed with one of these older Athearn non-genesis but post-blue-box units, and maybe this performance is normal with that setup?  When I get some time next week, I will dig out a couple comparable units to see what I get.

(In the meantime, I've started using the AORail Speedometer to do my speed matching. Much more enjoyable and much more precise!)
-Alex

What does the motor do when you disconnect the drive shafts. Run freely or what? 

Yes, the disconnected motor runs freely.

It would be interesting to compare the current draw of the motor with similar motors or to say it hasn't changed recently. Most of the DCC systems do not report a DC current so it's just a talking point. The NCE Power Cab has a total DC current which has been offset for the internal current, it's a useful value for comparison, but moot in most cases.

Using that system I did see a number of motors that increased in current draw and ran slower and slower, removing the drive line indicated the motor was pretty sick. There seemed to be some indication of the magnet becoming weaker. Talking with various help desks they either agree right away or put up a ' try this ' story suggesting it's the decoder or some other feature but not their motor. Go figure.

+ agree with the some sort of lubricant on the bearing or bearing surface where the motor shaft goes through the motor frame. I had thought that spot was heating up, expanding and binding the shaft, but eventually the motor did the low speed fade and high current story. Tried an Athearn Genesis replacement motor once, nice easy swap and the motor ran very fast with low current. Didn't match with anything else so technically not a successful swap. * after review holding off on Kato frames, need more research *
hth.



Edited 4 time(s). Last edit at 11/27/25 17:02 by TCnR.

I have the RRAmpMeter and could see what I get there for a current reading on the motor.  I'll get back to you next week on that.

I do also plan to dig out a couple other SD50's to see how they compare.

TCnR Wrote:
-------------------------------------------------------
> It would be interesting to compare the current
> draw of the motor with similar motors or to say it
> hasn't changed recently. Most of the DCC systems
> do not report a DC current so it's just a talking
> point. The NCE Power Cab has a total DC current
> which has been offset for the internal current,
> it's a useful value for comparison, but moot in
> most cases.
>
> Using that system I did see a number of motors
> that increased in current draw and ran slower and
> slower, removing the drive line indicated the
> motor was pretty sick. There seemed to be some
> indication of the magnet becoming weaker. Talking
> with various help desks they either agree right
> away or put up a ' try this ' story suggesting
> it's the decoder or some other feature but not
> their motor. Go figure.

Sounds like a tired motor. I just ordered a replacement motor for an SD40T-2 for the same reason. I cleaned the commutator, used Liquid Bearings oil on the motor bearings, didn;t help. It would start easy in one direction but need more power in the other.. Just a tired old motor.

Take the motor out of the chassis, clamp it in a hobby vice so the motor spins freely. Connect pos and neg wires from a toy train transformer (or a transformer with the correct specs) to the appropriate clips on the motor. Run the motor at full speed for 30 full seconds. Then, spray very liberally, a dose of WD40 to the brush contact areas and the bearing ends. You should see an immediate and dramatic increase in RPM's and thereafter a decrease in R's, but hopefully not nearly what it started out to be. I've been able to save many older Athearn motors that demonstrate the same issues you have. And again, I have had a few that just don't cooperate and get subsequently replaced. Oh, and make sure you put paper towels where the WD40 spray from the flywheels can be collected. Good luck. 

Why use WD40?  It's a water displacer, not a lubricant.  Check it out.  

Hello,
No DD40 looks like you have a connectivity problem use labelle 106 lube only on the gears. clean the wheel axles and the square brass parts with mineral spirits no lube there that is were the problem is.
Dave



Edited 1 time(s). Last edit at 11/27/25 21:37 by bnsfmodeler.

ExStarlightHog Wrote:
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> Why use WD40?  It's a water displacer, not a
> lubricant.  Check it out.  

Exactly. WD40 despite some is not the answer to all lifes problems. WD is flamible, when you spray it on the armature it creates a false connection. Check the brushes and while its running, rub a small piece of fine sand paper on the brass surface to clean off carbon and the WD40. Contact cleaner should always be used for cleaning and not WD. Sometimes when the fine sand paper cleans the surface youll see plastic where the brass has worn through. Bad amateur. Like most have said, highly likely weak magnets. Buy the genesis replacement motor.

ExStarlightHog Wrote:
-------------------------------------------------------
> Why use WD40?  It's a water displacer, not a
> lubricant.  Check it out.

Well it does lubricant, some what. But it's also a really decent solvent, which is what would help in this case. if you need to remove label adhesive forget Glue Gone, whip out your trusty can of WD40 instead. 

Pretty solid thinking though, if the WD40 doesn't fix it then toss it for being drenched in gunky stuff.

ChrisCampi Wrote:
-------------------------------------------------------
> ExStarlightHog Wrote:
> --------------------------------------------------
> -----
> > Why use WD40?  It's a water displacer, not a
> > lubricant.  Check it out.
>
> Well it does lubricant, some what. But it's also a
> really decent solvent, which is what would help in
> this case. if you need to remove label adhesive
> forget Glue Gone, whip out your trusty can of WD40
> instead. 

But Chris, WD leaves a film, thats what is designed to do. Disperse water and leave a protective coating behind to prevent oxidation. When it burns on the electrical surfaces the arcing will leave burnt carbon behind on the mating surfaces. Good for bearing surfaces, bad for electrical surfaces.

TomG Wrote:
-------------------------------------------------------
> ChrisCampi Wrote:
> --------------------------------------------------
> -----
> > ExStarlightHog Wrote:
> >
> --------------------------------------------------
>
> > -----
> > > Why use WD40?  It's a water displacer, not a
> > > lubricant.  Check it out.
> >
> > Well it does lubricant, some what. But it's also
> a
> > really decent solvent, which is what would help
> in
> > this case. if you need to remove label adhesive
> > forget Glue Gone, whip out your trusty can of
> WD40
> > instead. 
>
> But Chris, WD leaves a film, thats what is
> designed to do. Disperse water and leave a
> protective coating behind to prevent oxidation.
> When it burns on the electrical surfaces the
> arcing will leave burnt carbon behind on the
> mating surfaces. Good for bearing surfaces, bad
> for electrical surfaces.

Oh, I never said I would use it for this :-)

How freely does the chassis roll with the motor disconnected? if it seems stiff, you can clean the gearboxes out and fill with toothpaste and run it around for a couple hours, clean out the gear boxes again and fill with plastic compatible grease. That is the old blue box trick to breaking in a stiff gearboxes.

Ted Curphey
Ontario, OR

The motor seems to run fine at low voltage when it is disconnected from the gearboxes; the chassis is not all that free-rolling, so my suspicion is that it's the gearboxes.
 

Blue Box Athearns were famous for needing a drivetrain tune-up. Need to remove and clean up the gears, some had flash on the sides of the gears. Plus there may have been some slop on the worm gear requiring a thrust washer or two to tighten things up. Plus the need to get rid of all the old lubrication and to relube.

And to clarify, I only applied WD40 to the gearboxes, not to the motor...

In my opinion, the motors are good fishing weights. Speed matching them is very difficult because of the inconsistency in quality. I'm speaking from experience. You can get a few to run decent, but I was frustrated enough to change to Kato motors. Or the Genesis motors if yo prefer. Oiling motors is also a bad idea as if brushes get contaminated, it's another problem. Just my opinion 

dmaffei Wrote:
-------------------------------------------------------
> In my opinion, the motors are good fishing
> weights. Speed matching them is very difficult
> because of the inconsistency in quality. I'm
> speaking from experience. You can get a few to run
> decent, but I was frustrated enough to change to
> Kato motors. Or the Genesis motors if yo prefer.
> Oiling motors is also a bad idea as if brushes get
> contaminated, it's another problem. Just my
> opinion 

I like the suggestion to upgrade the motors - any recommendations on a source for either the Kato or Genesis motors?