AF Low Speed  Worm Gear Modification
A simple Modification to Lionel's AF Power Trucks to increase Gear Ratio.

Here is a simple modification to the worm shaft assembly in Lionel's American Flyer power trucks for improved low speed and switching duties. It increases the Gear ratio from 10:1 to 20:1 using a drop in modification. American Models uses this same principal by offering a optional set of low speed gears for their line of engines. It so happens that the AM gears can also be used to  for the same purpose to create a set of low speed gears that will work in American Flyer Power trucks too. The difference between the low and high speed worms is that the low speed has a single start helix and the stock worm is a double start helix. The diameter and pitch are the same.  The shaft that comes with the AM gear is pressed out of the worm and the hole reamed to .124".  Pull the worms off of the AF shaft and press on the AM worms and that's it.

The American Models Part is " Low speed worm gear on shaft" Part number "GBWSLS"  and costs $4.00 Each. You will need two for each power truck.

I would recommend this modification to any engine that you will be using for yard duty. I have it installed in EP-5's and Geep's and Baldwin's. The only down side of the is that there is a bit more gear noise at high speed. 

With this mod, you can ease the slack out of a train and never spill a drop of the Conductor's coffee in the caboose. 

This is the stock American Flyer gear shaft Assembly   Since I will be doing this to several Locos, and to simplify the process I made this gear puller from a cheap one inch "C" clamp. It is not a precision job, only requiring a grinder and drill press or mini lathe. I used a hacksaw to cut the slot in the clamp and filed to 1/8"width. Turning off the threads of the clamp for the punch shaft is easier with a lathe but could be done with a drill press.
Press off the stock worm with the puller.
Really easy with this little gadget
The Puller also is used to remove the shaft in the American Models replacement gears I used my mini lathe and a .124" reamer to size the holes in the brass worms for the AF shaft. One could use a drill press instead of the lathe.  I recommend investing in a reamer instead of a drill bit to resize the hole for a more precision job and it will not gall or grab.
Use a center punch to add some knurling to create an interference fit for the worm. You could also add a drop of Loctite to the shaft when pressing on the worms  Here are the Old and the New ready for assembly.
I used a drill press to press on the worms. I used a piece of scrap with a hole drilled in it for the shaft to extend down through when pressing on the worm.
The Puller is also useful to center the worms to match the spacing on the original. If  you used any Locktite be sure to make this adjustment before it sets. When reassembling the truck be sure that the bearings fit down into the depressions in the truck frame fully. 

Modifying Lionel's 

Here is the parts to do a Lionel Baldwin conversion. The shaft is factory knurled on the Baldwin and the worm is reamed to .125"  Shim washers have to be added in the Baldwin conversion
Due to tighter clearances in the Baldwin truck it is necessary to trim .10" off of the bearing blocks Here is the modified gear shaft assemblies ready to be installed in the truck
Since the bearing block has been resized you must add a shim between the motor housing and the truck frame. Be sure to center the drive gear on the shaft  so there is clearance on both sides.