Athearn F7 B BB Jumps at start

      I would checkout the motor on the locomotive. Pull the copper taps on the top and bottom of the locomotive and see how the brushes are wearing on the motor armature. One of the springs may be too tight or one of the brushes is sitting on the armature cockeyed. Be sure to clean the armature with a pensil eraser until the copper is bright and shiny.

   You may also want to make adjustments to CV's 3, 4, and 5 to adjust the starting, stopping, and mid speed range voltages..

   One other thing, you do know that athearn locomotives need the motors insulated from the frame. I have many old BB locomotives that i had to insulate from the frame when i went to DCC. I used electrical tape and clear silicone sealer to form an insulator between the motor and the frame.

If you use the washers that you mentioned on the worm gear one on each side of the worm gear should be sufficient..chuck  

 Thank You for the Answer Clark. 

 I have all ready set CV 2, 6 and 5.

 Any other thoughts?

 Ken

This sounds like an electronics problem to me. Have you tried another decoder, or tested the decoder in another engine?

I'm pretty sure the problem's not mechanical, since I've never experienced this with any of my engines before. I don't know much about DCC, so I don't know how much help this will be.

 Decoder problem, never would have though that. Will pull the decoder and install a chip that Athearn RTR come with from the factory to run on DC and see what happens.

 I have watched it happen with out the shell. Motor jumps till where it looks like the slack is taken up, then starts moving as I give it power.

 We will see later today.

               Ken

Could be a decoder problem or slack in the gears. I have a PA2 that does that when it initially starts in forward or reverse. Once the gear slack is taken up it runs normally. If I'm running it forward and stop it the n change to reverse the motor will turn to take up the slack then stop resulting in the loco bucking slightly then as the throttle is increased it'll start normally. When I change it back to forward it does tyhe same thing. If I have it going forward and stop then start forward again it won't buck because the slack is already taken up. Does that sound like what your F7 is doing?

I suppose the slack could also be playing a part in the problem. I'm sure you already know, but a washer or two on each worm should fix at least that. I still suspect there's something more, though.

 I am leaning toward Jeffery's thinking, the truck gears and worm gears came off a E-Bay buy so who knows how old they are.

 Brandon and Jeffery, if it is slack in the drive, where would I install the shims, front or rear of the worm gear? Can I use Kadee washers?

 Just got done running around and have not tested the B unit yet.

 I want to thank all that have taken a interest with the problem.

     Ken

I would use the Kadee washers if you have them laying around. It's easiest to put them on the front of the worm since the only thing there is a bearing. You're trying to stop the worm from shifting back and forth and that will be accomplished whether they're on the front, back or both ends of the worm.

 Well, Brandon must be right Jeffery. It jumps every time I move it forward with it running backwards.

 I like DDC why?

 Well, it is fun? Most of the time it is.

 See you all in the DCC section!