Lionel 1666 , can't seem to go in one direction longer than 10-12 inches before changing directions

First few things to check, is the track clean? How about the pickup slides? Can you test to see if power is flowing thru both slides? In the video, looks like it is going forward to the first gap in the track, making me wonder if one pickup slide isn’t working right. 1666s, my favorite loco!

I will try , one looks a little weak

Thanks

The E-unit is cycling because it's losing power.  It could be dirty track or blackening on the center rail, dirty wheels, dirty brushes or commutator.  Are the sliding pickup shoes (or their springs) worn out?  And for those on the Forum who have attempted it, how difficult is it to convert a 1666 to roller pick-ups, as used in the successor model 2026?

All 3 of my 2026 are early ones that also have sliders. I tried a roller from a 2018, it wouldn’t fit, was too wide for the slot where the slider went.

What type of transformer are you using?  The proper postwar transformer starts at 6 volts.  This is to operate the eunit before the loco starts to move. If you are using a transformer that starts at zero volts, the loco will start to move, then the eunit will operate when the voltage gets to 6 volts.

Using a ZW-L transformer .

I would really check the sliding pickup shoe assembly and all of the wiring as I noticed the headlight flickering on and off in the video indicating a interrupted current flow or a short. Hope that helps.

I think this is a combination of a couple  problems, the first being what David touched upon. The ZWL is a zero start transformer. So as David replied, your engine is beginning to move before there’s enough current to fully energize the E unit’s coil. So David is 100% correct on this. Second, possibly dust & debris on the track. To simply verify this issue, get the locomotive running in one direction or the other, and flip the lever to turn off the E unit. Observe its operation to see if you experience stalls that also make the headlight blink, or go out completely. This would indicate a loss of connection. Then suspect sliding shoes, dirty wheels, dirty/dusty track, etc. …..

Pat

cold solder joint or loose wire

Agree with Dave -cold solder joint or loose wire.

Also it could be a loose e-unit lever had one postwar loco with that problem going about half way around 4x8 layout the lever was then slightly bent inward so it would not move unless by hand which fixed problem.

Anyway many times the e-unit needs to be looked at carefully .

Spring tension on the sliding shoes or a loosen e-unit lever.  I use a “L” shaped tool make from a coat hanger that is slipped under the contact spring, then a screwdriver is used to bend the end of the spring down so it exerts more pressure on the sliding shoes.  Likewise, a set of duck bill pliers ground down to fit between the coil and rivet to tighten the e-unit lever rivet.  Also, gargraves, fastrack and realtrax don’t have a raised center rail like tubular track which reduces the contact pressure on the center rail.

Thank you , everybody !

I will try