MT F7 Rolling Mods

 

Index:

Powered Truck Mods

Dummy Truck Mods (The Easier Fix)

Dummy Truck Mods (The Ultimate Fix)

Frame/Weight Mods

 

Powered Truck Mods

My powered F7A unit seems to be a fairly strong runner, but had a very poor slow speed and annoying grounding sound. It turns out that the plastic truck frames apply pressure upward on the wheel axles, which then apply that pressure upward on the metal truck blocks to increase electrical pickup and continuity. This obviously creates a great deal of friction, which overworks the motor and causes the issues I raised. I believe this is why the newer dummy units now come with shims that act as a spacer and pressure/friction reliever, if you will.


I did some tests by simply un-tightening the screws which hold on the plastic truck frames and the unit ran much more smoothly. So I added my own spacers and tightened up the screws so they don't fall out. I haven't noticed any difference in electrical pickup continuity, but I'm not overly worried about this, since I will be adding DCC and caps to act as an electrical fly wheel (see F7 DDC & Sound section).

Shim added:

This shim was created from thin styrene and seems to do the trick.

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Dummy Truck Mods

Many of the new units come with shims which alleviates some of the pressure that the plastic truck shells applies to the bottom of the axles. On my particular units, these shims did not help much. The uneasy rolling is simply caused by too much friction on the axles. Others also claim bent axles and out of gauge wheel sets contribute to its poor rolling factor.

Original:

Here is a shot of the original metal truck blocks.

Truck Frames Modified:

I filed each truck block half in less than half of its original thickness to create less point to point contact between the axles and truck blocks.

Axle Well Modified:

To get even less surface area riding on axles, I filed what was left to a rounded point.

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Dummy Truck Mods (Version 2)

Although the above truck mod helped, I still felt there was too much drag created by these locos. So here's attempt two, which should do the trick. The drag obviously comes from the metal frames hugging the top of the axles. Although limiting this surface area helped, the best way to reduce this friction was to resort to the traditional method of mounting the wheels where only the axle ends contacted the frame for its support. Since these wheel sets don't have the pointed axle ends, I replaced them with Marklin metal wheel sets, such as the ones found on their loco tenders. In order to mount these, a journal to hold the axle ends needs to be created. This mod renders the trucks electrical pickup useless, unless wheel wipers are installed.  TeeterTotterTreeStuff(under "Wheel Wipers") makes wheel wipers specifically for the MT F7 units, so I will do some more testing with them as time permits!

Find the Center:

A #80 hole was drilled from the outside of the truck frame right in the center of the journal. The molded in journal will line the drill bit up perfectly and you will not even notice the hole later on. Remember to keep the drill bit parallel to where the wheel axle will be.

Opening up the Journal:

From the inside of the truck frame pointing downwards, the hole was enlarged with a #75 bit. This should only be drilled in slightly so that the larger bits can line up on the hole. Then the hole was enlarged with a #70 bit as far into the truck frame as you can go, without going through it. And once again the hole is enlarged with a #61 bit, about half way through the frame. If you accidentally drill all the way through the frame, since the wheels and axles are tinted black (in some cases), the colors blend in with the frame and it is very hard to even notice the error.

Truck Frame Mod:

Some extra room needs to be cleared out for the inner shape of the wheel with small file.  The left truck is the original while the right right has some plastic filed out for the wheels.

Pop the Wheels In:

Slide the wheels sets in.  It is a tight squeeze, so be careful.  If you need to lightly force the wheels into place, use a pair of needle nose pliers, but do NOT force the axle as this may bend it and cause wobbling.  The best place I found to grab the wheel is the inner like wheel on the inside of the flange.  If the plastic side frame breaks, a dab of your favorite plastic glue will be plenty strong enough to hold it.

Metal Truck Frame Mod:

No need for this anymore. Cut both ends off and smooth with a file.

Putting it Together:

Put the frame back together with out the shim, if you originally have them. Besides the fact that you don't need the shims anymore, since the new wheels are slightly smaller than the original, removing the shim will help get a little more ground clearance between the bottom of the truck frame and the rail head.

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Frame/Weight Mods

I don't see any reasons why the dummy units should weigh this much unless they are being used for power pickups. So I cut out as much of the frame as possible, including the metal cones rising out from the frame. This also allows for the placement of the DSX chip and speakers (see F7 DDC & Sound section).

A powered unit:

Not much can be done here.

B dummy unit:

The speaker will face down, so we need to cut a path in the frame for the sound to travel through and bounce back up off the track and road bed. The shell will act as a speaker cabinet and enhance the sound.

B dummy unit:

The mangled DSX chip will fit right in here. Note that the securing tabs from the truck frames were cut off to allow more clearance.

A dummy unit:

This frame will mimic the speakered B unit.

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