Trying to solve a mystery truck problem

[jonathan]

I have an Athearn diesel from around the 1990's (it has brass flywheels).  Today when I ran it, it seemed significantly slower than my other Athearn diesels from the same decade.  When I got down close I could hear a thump, thump, thump (about 4 times per second at 80% power).  I isolated it to the rear truck.  Took the truck apart and couldn't find anything.  I suspected something was misaligned, just couldn't find it.  After I put it back together, everything seemed alright until I put it on the track. The rear truck is somehow robbing power from the rest of the engine.  If I give power to just the front trucks, engine runs fine.  If I give power to the rear truck, it drags to the point that the power pack trips and I have to wait for the reset.  Something is wrong, but I can't figure it out.  The truck is in the correct orientation (not backwards). Just haven't been at this long enough to  noodle it out.

Here's a pic I took a while ago of the guts


Here's the rear truck


On this engine, I ran a wire up from the bottom motor clip to wire the lights.  You can see One of the lights is connected to the tab that connects the rear truck.  I'm stumped. 

Is that enough info to diagnose?  Could over lubication cause this?

Regards,

Jonathan

[Nigel]

My first guess is a split axle gear.  Try swapping one axle at a time with the other truck.

[jward]

it sounds to me like something is binding in the gearbox. remove that truck from the locomotive frame and worm gear. it should roll freely by itself, like a freight car truck would. if it doesn't you'll have to take it apart and carefully inspect each gear for any foreign material between the teeth. if the gears have been greased you'll have to remove the grease in the process. a screwdriver blade works best for cleaning the gear teeth. remember, in a properly working gearbox every gear rotates freely.....

as for the split axle gear problem, while that would definitely make the clicking sound it wouldn't load the motor down to the point of overloading the power pack. if anything it would decrease pulling power, not speed. your problem almost has to be a gear bind.

[jonathan]

Jward and Nigel,

Thanks for your replies!

I have completely disassembled both trucks, inspected gears, wiped everything down, in case I was overzealous with lubricant, and reassembled.  Trucks seem to move freely.  No split or broken parts.  Perhaps I dislodged something.  Anyway, now the loco will run great for two minutes (I timed it).  Then, the power pack trips.  When I spin the flywheels with my finger, everything seems to turn freely, the thumping is gone anyway.  The motor doesn't feel hot, or even warm.   For the two minutes it's running, it seems to run the same speed as my other Athearns of that decade (put two on the track at once).

Cleaned the commutator, just in case.

Still playing with it.  I keep thinking I wired the lights wrong somehow.  But they light up fine when the engine is running.  I'm electricity ignorant, so I keep thinking it's operator error.  Somehow I'm overtaxing the motor through funky wiring.  Is that possible?

Regards,

Jonathan 

[jward]

sound like something is shorting out, this is a different problem than the thumping.
does this locomotive trip the power pack when standing still? does the pack trip when the locomotive is at a particular location? is the motor warm when the power pack trips?

electrical troubleshooting usually is easier if you have an ohmmeter. i've seen them as low as $5 at auto parts stores.

the procedure is to isolate the various components of the locomotive then measure the resistancewith the ohmmeter. ALWAYS do this at the workbench, where no power is applied to the locomotive.

since the motor is low resistance, start by disconnecting it. carefully remove the top clip, making sure that the motor brush spring doesn't pop out. the motor will read low resistance. the lighting system might as well, so disconnect that next.what you should be left with are the two trucks in the chassis, with the motor lead connecting the top brackets on the trucks. you should read infinite resistance between the chassis and the top brackets. checque to make sure that the brackets do not wiggle in the trucks, as this may cause shorts. if you read low resistance, then disconnect the motor lead from the top bracket on one of the trucks and remove it from the chassis. checque to make sure that the metal bolster tab (where the chassis rides on the truck) is not touching the top bracket where it enters the truck frame. repeat with the other truck.

if your reading was infinite resistance while the trucks were still in the chassis, reconnect the motor clip and run the locomotive. if it runs normally, your lighting circuit is at fault. if it doesn't replace the motor.

[jonathan]

Jeff,

Thanks, I will try the ohmmeter at the earliest opportunity.  If it turns out to be the motor (wouldn't surprise me), I'll be between a rock and a hard place.  Two of these kits were inexpensive and two were free.  If fact, a motor ($50+ with shipping) would cost more than I have invested in all these kits put together.  I like 'em but I've gotten brand new P2K and Bachmann locos, at train shows, for $50.  Here's hoping it the lights....

Thanks a million

Jonathan

[Jim Banner]

In your top photo, the right hand end of the motor is sitting high.  It could be the fat wire to the bottom brush clip or the rubber plugs not properly in their holes.  In any event, the drive shaft is sitting at a steep angle which was probably both your clicking and binding.  Make sure both drive shafts are horizontal, or nearly so.  I also see some excess wire which might be binding against a drive shaft or more likely a flywheel.  Thirdly, I am concerned about the quick connects - they look like they may prevent the trucks from swivelling properly.

Jim 

[jonathan]

Jim,

I took this photo right after I finished wiring the loco.  The motor was in fact not seated properly at the time.  I was able to push it back into position, but I find I check it often.  Perhaps I used wire that is too thick down by the bottom motor clip.  I would be willing to bet that causes the intermittent clicking or thumping.  Now we're getting somewhere.

This morning I ran the loco on my test loop, which is some 15" radius stuff with an old Tyco  power pack.  I ran for about ten minutes without tripping the pack.  However, I had the power around 90% to get it to run at what would seem a 50-60% range.  The motor was very warm, but I could still keep my fingers on it without burning myself.

Then I ran it on my regular loop, for about 10 minutes, pulling about 10 cars.  Power pack did not trip this time.  Motor was a little warmer than I think is normal.  Feels like I have to feed more power than normal to this loco.  Perhaps I just need to replace the thick wire, with some thinner stuff.  I tend to use whatever is handy on my work bench.  I could not tell you what gage it is, but it is thicker than the wire I see inside the Ready to Run locos I own.  I used the same thick wire in all the GP kits, but soldered directly to the truck tabs, instead of using quick connects.  Also used really thin wire for lights.  Perhaps I'm getting somewhere.

Thanks so much again, Jim. I'm learning....

Sincerely,

Jonathan

[pdlethbridge]

When you soldered the clips on the top and bottom of the motor, did you have them off or on the motor?

[jonathan]

They were off the motor.  Great question, though.  The first time I hard wired a GP40, I left the clip on.  I know that's a potential for disaster.  THAT engine still runs, thankfully.

Hardest part was keeping the brush springs from playing hide and seek with me.

Jonathan

P.S. After a little soul searching, I have decided that I will pursue new motors for all my old GP kits... and the right sized wires!  I really like them, have enjoyed tinkering with them, and want to make them good runners.  After all, I have been adding little detail parts here and there.  Why not make the inside as nice as the outside.  The best part of this hobby is building your own rolling stock, one piece at a time.  These will be a-little-bit-at-a-time projects.  Thanks for the tips and advice.  The great helpers like you on this forum, make this that much more enjoyable.

Regards,

Jonathan

[jward]

athearns, while not up to to-day's standards, were great locomotives in their day. my dad and i made them the backbone of our respective fleets for many years. it is a testament to how much quality of drives has increased in the last twenty years that these locomotives are now among the least desired.

properly maintained, there is no reason an athearn locomotive won't last you twenty or thirty years.....

[BestSnowman]

Hey Jonathan I just noticed this post and have some thoughts to add as I have been working with a SDP40 with same style drive train (just longer).

I had an issue with one of the trucks after reassembly that matches your description and I was able to resolve it by swapping the location of two gears that were the "same" size. Not sure why but since mine is 20+ years old I just accepted it and made a note to remember that.

I also had a similar shorting problem that was caused by the two pieces of metal that bring power from the trucks were two close. On the my SDP's trucks, and I suspect your GP's there are two L brackets. One delivers power to the frame where the frame sits on the truck. The other is on the other side and reaches up above the axel. What happened to me was the upper bracket had bent in slightly so they would come in contact after bumping around on the track for a bit. I bent one outward a bit and the problem disappeared and it ran quite a bit better.

Another thing to consider is the wheelsets if its an older Athearn. They used sintered steal which leaves a rough surface that can result in carbon build up and pickup issues (I'm not a first hand expert on this, just based on my adventures with the SDP40). I bought a wire brush dremel attachment and polished the heck out of the wheels and got a lot better pickup and performance.

[jonathan]

BestSnowman,

Thanks for the tip. I've gotten pretty good at disassembling the trucks, so I'll have a look at the orientation of the L brackets (and gears).  I wonder if a bit of paint in the right spot will prevent the short as well? Now that I've gotten a bit better at wiring, I'm actually thinking of bypassing the frame and soldering a wire directly from the metal side of the truck to the bottom clip of the motor, or whatever motor these engines get. 

I have to say I like the iron wheels so far.  I have cleaned them and coated them ever so slightly with conductalube.  The traction is better than my other locos.  No problems with pick up so far (time will tell). I'm hoping that I keep these babies running long enough that they wear down smooth and shiny with age.


Regards,

Jonathan

[jward]

painting the parts to insulate them is a temporary solution at best. if they rub and short out, they will rub the paint off and short out eventually. the trick is to keep them from rubbing in the first place.

if you need to adjust one of the metal tabs, adjuct the flat one with the bolster hole  where the chassis rides. the tall one that conducts power to the top of the motor will work loose inside the truck if you adjust it too much. then you'll have all sorts of problems trying to secure that tab.

bypassing the chassis with a wire soldered to the metal plate inside the truck is a very good idea. while soldering this wire to the bottom clip of the motor, take the time to insulate this clip from the frame with electrical tape and you've just made your locomotive dcc ready.

[jonathan]

OK,

Thanks, Jward!

The bolster tabs seem to be alligned correctly and are not touching anything on the other side of the truck frame.

I'm all set to solder the truck to the bottom motor clip.  I notice the inside of the truck frames are all plastic. Where can I solder that won't melt the inside of the truck frame?  I could solder to the bolster tab.  There's no plastic there.  Is that a good spot?  Also, will I need to put a fiber washer between the tab and the bolster, where the tab marries up to the frame?

I also notice that the motor brush is concave where it meets the commutator.  When I reinstall, will the brush seat itself, or do I need to manipulate it so it is alligned?

Quick, I feel a PD headache coming on!

Thanks a million.

Jonathan