Atlas SD50

[davefoxx]

Forum,

I've got two old Atlas SD50s decorated for the Seaboard System, so they may be pushing ten years old.  My problem is that they were slowing down in sharper radius curves.  Last night, I tore both units down to clean them up and to see if I could improve performance.  First, I swapped out the motors for newer slower speed motors.  I also took the trucks apart to lube and address any gauge issues.

Now, I have one SD50 that runs fairly well counter-clockwise (left hand turns) on my roundy-round but not as great clockwise (right hand turns).  The other locomotive slows significantly in turns in either direction.  My only thought is that it is related to the lash of the worm and worm gear.  But, why can I get one to do okay in one direction?  I guess this helps eliminate any question of the trucks binding in curves.  Besides, when I put the trucks back together, I was careful to ensure that each truck rolled smoothly before being put back into the frame. 

Thoughts?  As another option, do later models of the SD50 or SD60 (I think they're the same mechanism as the SD50) run better?  I might be seriously tempted to just purchase new mechanisms and swap shells, if this solved the problem.  The SD50 was some of the latest power on the Seaboard System, so I really would like to get these models running well.  Besides, I like these big locomotives, and they provide a nice contrast to my four-axle fleet.

Oh, and I don't seem to have a center-axle "tapping" issue, so there is no need to get into that issue in this thread.  That issue was covered well several years ago on the A-Board.

Thanks,
DFF

[ArtinCA]

Dumb question, try swapping trucks between units to see if the problem happens?

[Iain]

If they do only left hand turns well, enter 'em into Nascar! 

[Wlal13again]

I have the same problem on a GP40-2 Dave...

[davefoxx]

I have the same problem on a GP40-2 Dave...

Rich,

The suggestion to try different trucks might work well for you.  Give that a shot.  I have a feeling something's going on inside the gears on your GP40-2.

DFF

[jagged ben]

You've checked the gauge on the wheels?

[davefoxx]

Yes, when I put the trucks back together, I carefully gauged the wheels and ensured they would not only roll through 11-12" radius curves without binding, but also through the frog area of my Atlas #5 turnouts smoothly.  I will try to swap trucks between my SD50s to see if there is a difference.  I hope that is the case, and, if so, I found replacement SD50/60 trucks online at Atlas' website and on eBay.

I checked the date of manufacture online, and the Seaboard System SD50s were released in 1999.  They're almost fifteen years old!

DFF

[LV LOU]

Just what radius are these "sharper curves",and what kind of track are you using? Atlas C80 could cause problems if installed in the wrong direction..The moveable rail should be outside..

[Kisatchie]

The moveable rail should be outside..

I heard the moveable rail should be on the inside of the curve. Let's have a vote  .


Hmm... I know, but I'm
not saying...

[Wlal13again]

Rich,

The suggestion to try different trucks might work well for you.  Give that a shot.  I have a feeling something's going on inside the gears on your GP40-2.

DFF

Thanks Dave, I will try that...

[davefoxx]

Okay, I tried swapping trucks on my SD50s, not only between the units but also end-for-end.

1) When swapped end-for-end, the performance of the good SD50 decreased.  So, the trucks seems to be where the trouble is coming from.  When I put them back, the performance returned.  Whew.  At least, I can run this thing counter-clockwise around my loop until I get this worked out.  I'm still wondering about that worm gear meshing with the worm.

2) When I swapped the trucks end-for-end on the poorly running SD50, it got worse.  In fact, it ran better on the curves than the straight track.  WTF?!

3) When I swapped trucks between the units, it did not improve the performance of the bad SD50.  It may have run slightly better, but it still slowed in the curves.  It definitely didnt run as well as the other SD50 on those trucks.  So, I put the trucks back on the other SD50, so I do have one unit that I can run for now.  Counter-clockwise anyway.  It does run okay in forward or reverse, as long as it is pointed (cab end) in the counter-clockwise direction on the layout.

I'm really tempted to just order two pairs of SD50/60 trucks and see what will happen with new trucks.  Thoughts or further suggestions?

DFF

[davefoxx]

Thanks Dave, I will try that...

Don't hesitate to Beardenize that GP40-2 while you're at it by removing the inner bearing blocks.

http://trainweb.org/passengercars/Bearingblock.pdf

Unfortunately, because of universal joints, I cannot do that trick to improve the performance of Atlas SD50s.

DFF

[jagged ben]

Okay, here's a couple questions. 

Do the trucks sit level side-to-side inside the mech?  Does the mech sit level front to back?   

The Atlas SD50/60 trucks have a design flaw in that there are these little horizontal pins at the top of the truck towers on each side, and the whole mech rests upon them.  They are small and easily broken.  Once broken the whole loco sits and the wrong height or leans to one side, and you get various types of problems, from gear binding to bad electrical pickup.

I would check for that.  If you are already ordering new gear towers, maybe order a couple more. 

[Bendtracker1]

Dave,
I have a couple of these older SD50's and never had any problems with them, but the next time you have them apart, take a straight edge and lay on the inner face of each frame half and see if they are flat or if there is any warp to them.  This might cause one or two things that might add up to your problems.
If they are warped inwards, they might bind on the truck towers or the pins that hold them in the frame, or it might make the bearings set just out of alignment which would cause drag.

Speaking of bearings, make sure they are set in the frames properly.  If they are not they would be putting pressure on the shaft in one direction more than the other.  If you've ran these for awhile the bearings might also be worn enough so they don't hold the shaft in the proper position.  Since they are that old, the plastic block that surrounds the bearings might have deteriorated or gotten brittle enough to not hold the bearing properly.

At this point I'm only casting lines in the dark, but it might be worth a look.

A word of caution about getting new trucks, I had some older Atlas/KATO Gp35's that I swapped the frames for some newer DCC ready frames not long ago.  Since the old 35 trucks and fuel tanks were painted and weathered, I just swapped out the frames and used the old trucks and tanks.  After I did this, both sets of the old trucks in the new frame were very stiff.  I wound up taking the dremel and two small grinding bits and ground out the areas where tips on the truck towers locked in the frame as well as the areas that surrounded the towers just a bit to widen them out.  Afterwards they swiveled just fine.  It was almost like the new frames had closer tolerances than the older frames did.

Not sure if any of this will help, but it's worth a shot at this point.

[davefoxx]

Okay, here's a couple questions. 

Do the trucks sit level side-to-side inside the mech?  Does the mech sit level front to back?   

The Atlas SD50/60 trucks have a design flaw in that there are these little horizontal pins at the top of the truck towers on each side, and the whole mech rests upon them.  They are small and easily broken.  Once broken the whole loco sits and the wrong height or leans to one side, and you get various types of problems, from gear binding to bad electrical pickup.

I would check for that.  If you are already ordering new gear towers, maybe order a couple more.

Whoa!  I need to look at that.  The problems that you suggest are what I'm dealing with, including some poor electrical pickup that I attributed to dirty wheels since these locomotives have sat for so long.  The locomotives seem to sit level and straight, but let me go tear them down again and see if I can find whether the pins are broken.

Thanks,
DFF