MT SD40-2

I purchased a Micro Trains SD40-2 in the older blue and yellow Santa Fe livery.

I put it on my modules and fired it off under DC. The first thing I noticed is that it runs much slower than my MT GP9s. The second thing was that this one seemed to surge a bit. It also ran a bit funny, and derailed. Later the snowplow came off. I stuck it back and on it was fine. It was probably just loose and hanging down.  I left it running for about 6 hours and it smoothed out. I ran it about 4 hours backwards. After this time it seemed to no longer surge and seemed to have a bit higher top speed.

I noticed that the headlight "bleeds through" the cab roof also. I did not see the rear headlight come on, but since I am going to DCC this, I did not look further than a cursory glance.

Right off the bat, you see how low the center of the trucks hang. The trucks look great from the side, but you can see that there could be clearance issues.

Disassembly

Pop off the fuel tank, comes straight off (downwards). The fuel filler caps are towards the cab.

Remove the shell. Hold the top by the dynamic brake blister, and hold the metal part of the chassis and pull straight apart. Some can be very hard to remove, don't press on the handrails!

The rear headlight shroud will probably fall out, it's a small black box.

Next, you want to remove the brass wipers that bring the power from the trucks to the chassis halves. In the picture above you see the right side one, and you can see the small brass "pin" on the truck that touches the underside of the end of the long brass wiper strip. Just pull it out sideways, trying not to bend it. I used a small screwdriver between the wiper and the chassis. Note the orientation and keep them separated so you remember which was which.

Remove the motor springs. As with any MT loco, these are fragile, and it's easy to lose them or bend the loop out flat.

Before doing anything else, measure your chassis width to know when you have it back together right. .325 seems to be ideal. Remember that if you don't get it back together "narrow enough" you won't be able to get it back into the shell, or it can wind up trapped inside.

Unscrew all 6 screws 1 turn, put a flat blade in between the halves and spread them a bit.

Pull the trucks off. The end of the truck with the projection goes towards the fuel tank, as you can verify in the picture above.

Inspect each truck for free rolling, no resistance in the gears, if problems, pull them apart. One new loco had one wheelset out of gauge by 1.5 mm!

Now pull the old circuit board out carefully, it has to be clear of all 4 posts to get out.

DCC install (TCS "drop in"):

file the slots in the posts to the thickness of the new board, carefully!

file a 45 degree bevel on the top 2 inner corners of all 4 posts

fit the decoder in place.

The horizontal location of the rear LED on the TCS decoder might make it hard for the light shroud to fit properly, if so, just hog out the hole in the end of the shroud to let it fit nicely to the chassis.

Reassembly:

As with other MT locos, the "motor springs" are at the front end of the loco.

Don't forget the LED shroud on the rear light.

Tighten the screws to get the loco thickness back to where you measured it earlier.

Tips / Improvements:

Snowplow:

The snowplows are not glued on and hang down quite a bit. If you aren't careful, you will lose them. I glued mine on with a touch of solvent glue, and while the glue was setting up, suspended my loco on 2 spools by the bottoms of the snowplow. This forced them to set in a position as far away from the rails as possible. Many people glue the snowplow on and then trim the bottom, but this way makes it so you don't necessarily have to do the trimming.

Erratic running:

I had some erratic running after a while. It would stop on the expanding rails. The first thought would normally be gauge problems, but it ran fine before. Turns out that the brass contact strips can get bent so that they can hang up on the contacts on top of the trucks and restrict the motion of the trucks swivelling.

SD-40 advanced tips