Is it my Legacy or is it my engine???

Check your command base wire connection. Also, I own a legacy GP7 and on mine the flywheel with the tach reader came loose on the motor shaft which threw off the speed control. The loco would randomly "take off" because the flywheel was slipping on the shaft and spinning slower than the motor itself. this spins the tach reader slower making the speed control "think" the engine is going much slower than it is so it overcompensates.

You can remove one of the roof hatches to observe if its slipping you want the one with the black plastic ring attached to it. You can even try spinning the flywheel with your finger and see if it turns the wheels, if not, its loose.

Its been a while since I tightened mine, it was either a tiny allen key or a small flathead screwdriver an eyeglass screwdriver works well. I've seen Lionel flywheels with both types. 

 try it in conventional?Did you get smoke fluid on the red thumb wheel or controller?

RickO - Connection was tight to the base, Putting pressure on the gears underneath I was able to turn the flywheel and all seemed OK. The tightening screw you spoke of, I assume the shell needs to come off to access it??

Patrick H - Conventional appears OK, no smoke ever near the controller.

I assume you checked the command wire at the track as well, if this layout is on carpet sometimes the "undulation" of the track can work the connection lose.

Is the base plugged into the wall or a powerstrip? Some power strips can degrade the legacy signal.

If not that, try resetting the loco. The steps are in the owners manual if you have it handy, it can also be found on Lionels website, of course.

Look for "reprogramming loco to restore functions" its usually found towards the back of the manual.

Fixed!! - Engine reset was the trick! Thanks Guys!

OK, maybe it's not fixed. After the reset it ran probably 3-4 hours yesterday with no issues.

This AM I had it running again when it took off like a bat out of he... Grabbed the remote, turned the speed down til it stopped. Once stopped I went to move it again and the sounds escalated like they should but the engine did not budge.

I shut everything off and restarted and it ran. 

So, what say you now?!

Thanks!!!

Are you saying it ran continuously for 3-4 hours?, it could be something heat related.

It sounds like something related to the speed control, an email to Lionel tech support may be in order. They don't just set up warranty repair, they also can recommend repairs/parts if you wish to do them yourself if somethings out of warrranty.

I'm surprised you haven't heard from  some of our resident TMCC/legacy gurus on this matter. 

Could the Brake/Boost rocker switch be engaging because of dirt, bad switch, or other?  Otherwise my next go to would be the fly wheel which you checked. 

Look ok at the Cab 2 and see if where the ENG display there is an up arrow displayed. 

My bet is perhaps either a temperature sensitive component or a loose plug/board that occasionally causes the issue to surface.

John - I would certainly agree with heat as a potential cause, but I would have expected that yesterday after 3+ hours. Today it was going 5 minutes before it went bonkers!

LHS suggested speed sensor on the motor and made it sound like replacing the entire motor might be easier.

Just to be sure Jeff, when I mentioned the flywheel, you checked the one under the short hood correct? I noticed mine slipping when I ran it with the hood off and I watched the flywheel slow down as the loco sped up.

The screw for the flywheel is recessed into the side of the flywheel and the shell must be removed for access.

Postion of the ring in relation to the reader is important also, if the flywheel is loose  and wlks up or down the motor shaft it could throw off the reader.There are arrows on the reader that show where to line up the bottom of the tach ring

This is the one with the tach ring and speed reader its very easy to see.

Its been a while since I had the shell off of mine but I believe the speed sensor is mounted to the motor and its a matter of removing the flywheel and R&R the sensor board.

If it's not heat, it could simply be a loose connection.  As Rick says, it might indeed be the sensor and/or flywheel.  I don't know that all these motors with the sensor have a setscrew to remove the flywheel, in which case it may be easier to replace the entire motor assembly.

Rick - When you say short hood, I assume you mean the front of the loco? As I see it the only way to get at that is removing the shell. I have not taken the shell off yet, but it appears I will be.

I will report back on what I find.

Thanks.

On the GP7s both hatches above the motors lift off.  You'll be able to trouble shoot the flywheel with just the hatch removed but will most likely need to remove the shell if it's indeed loose to tighten it.

Its the top access hatch, its held on by magnets. You can gently lift it off by the horn.

Long Hood.

Short Hood.  This is the Legacy Flywheel with the tach ring.

Wow, talk about a great fit.

Popped off the cover, turning the flywheel by hand I can feel the wheels move even as I apply a little resistance.

Jeff,

   I would suspect the motor encorder board on the motor. If that's the problem it can easily be changed, no need to replace the motor. Other possibilities are mother board, motor driver, broke wire to the encorder. 

Bill 

Thanks Bill.  Any way to positively ID the problem? I'd hate to just start changing parts.

Mine has been doing this. Being that I am about 3500 miles from Ohio, I sprayed the switch with electrical contact cleaner (Plastic safe stuff). This appears to have done the trick.

I had a Legacy loco do the run away trick. It turned out it was a faulty motor driver board.

Update. Turned it on this AM it ran for about a minute before it took off. I ran one lap around the tree then returned to the speed I had set. Thirty seconds later it took off again. This time as well, one lapped then it stopped. I had to shut everything down to restart. It is now off the tracks.

Seeing how it was barely going before it took off I think would eliminate the heat as a potential problem.

Now the Cab 2, it was not in my hands but setting on a table as I had the speed set.

Today I'm going to pull the shell off and take a look.

Jeff you have mail.

Bill

Bill do you have something to add?  Something the rest of us could learn from. 

Yes I do, and that is why I sent the email to Jeff. I told Jeff to call me so I wouldn't have to type how to trouble shoot his problem. If we fix his problem then he can explain how we did it. It will take to long to question and reply.

Bill

Gotcha. Thanks.