Welcome to the forum!
A few quick questions to start with.
Do all your locos exhibit the same problem on all your switches, or just some/one?
Have you cleaned the track and the switches also? Use hardware store naphtha to clean track/switches/wheels/rollers.

If you have a voltmeter, check for proper voltage along the entire length of the center rails of the switches.
If you do not have a voltmeter, but have a lighted car, roll it slowly by hand over the switches and see if the light goes out at any spot on the switches. You can expect a loss of power as you traverse the gap between the wide center rail, and the normal rails. If your locomotives have 2 roller pickups, it could be possible that only 1 is receiving power, and as you traverse the gap, the locomotive will lose power and stop.

Next, run a locomotive alone through the switches very slowly until it stops. Turn off the power and get your head down on the rails with a flashlight in hand and physically observe exactly where the locomotive stopped, and the relation of pickup rollers to the rails. Some locomotives have very wide pickup rollers, and when going through the switches, the rollers bridge the center rail to the swivel rail and short out, cutting power and putting the locomotive in neutral.

Run these tests, and see what results you get.

Larry

Don,
To test the voltage on the switches, set your meter to read AC volts, and put one lead on the center rails, and the other lead goes to the outside rails that do NOT have the insulated pins in them.
These rails are the ground connection.
One rail would be the entire straight outside rail nearest the switch machine, and another would be the curved outside rail JUST OPPOSITE the switch machine.
The curved outside rail WITHOUT the insulating pin is also ground.
Lastly, the swivel points are also ground.

Turn up the power and measure the voltage at the transformer terminals, the lockon, and on the switches at the described locations.
The voltage readings should be the same, or within a volt difference. Any larger variation of voltage at any point needs to be investigated and corrected.

If your lighted car did not exhibit any problem on both the straight and curved paths of the switch, chances are the switches are receiving voltage properly. Check the voltages anyway, to insure you do not have any voltage drops anywhere.

When finished checking the voltages, run a locomotive slowly until it stops, and report back exactly where it stopped. Upload a picture of it if possible.

Larry

Welcome Donbara,

Try uploading one more time.  I deleted several giant photos to create space.   

Don,
Glad you found the problem.

What is the number of the locomotive? All rollers are not created equal, and the correct one must be used. Roller sizes vary, as does the mounting method.
There are 2 different rollers that mount in similar roller arm assemblies, one that has the roller and pivot as one piece, and the other roller that revolves around a separate pin that gets clinched over on one end.
Which roller do you have on your loco? The picture is not clear enough to see that detail.

Larry

The roller is part #2035-140, and the roller pin is #2036-124.
The entire roller bracket with the roller installed (easier to replace) is #2035-142.

Parts are available online from Brasseur.
http://www.traindoctor.com/service/lionel/1600to2100.php

Larry