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Converting 4v Lego train motor to 9v?

Hi! I am not slowly becoming a Lego person because of my son and husband but I have a question. We have the vintage Lego train set 7722 and the 4v motor and/or battery box/extension wire is not working. We tried to get a "new" motor from ebay and it still didn't work. Any chance I can convert it to the 9v setup? There are many more motors available in working order for that one. I don't want to have to buy a whole "new" (used) 7722 set when ours is pristine but not working for some reason. Any advice would be helpful. Thanks!


  • oldtodd33oldtodd33 Member Posts: 2,683
    Hello, The most likely reason your 7722 is not working is because the connecting wire has a loose connection. The problem is most likely at the metal connectors. They tend to crush over time being inserted in the motor or battery car and tend to stay crushed when you pull them out.

    The best way to fix this problem is to gently insert a hobby knife blade first in between the prongs and GENTLY pry them apart. Being careful not to cut yourself with the razor edge. Do this for all four parts of the connection until they look evenly spread but not so much that you can't insert them into the connections at the battery car or motor. This will solve the non-working condition 90% of the time.

    The 7722 also lends itself to being converted to 9v very easily. Simply remove the 4.5v motor and build the 9v motor into the frame of the 7722 engine. I did this several years ago and it looks good and works great.
  • alwaltzalwaltz Member Posts: 3
    If you convert it do you need a different battery box or wire? Thanks so much! We will try the prong thing first
  • oldtodd33oldtodd33 Member Posts: 2,683
    If you convert it to 9v, you need to have the whole 9v system including the track and controller with transformer. Otherwise, buying just the motor won't do you any good since the plastic track that comes with the 7722 doesn't work with the 9v motor. The 9v system runs on plastic track with metal rails on top to provide power to the 9v motor since the 9v system is not battery powered. If you don't have the 9v system pieces at all it would be a lot easier to just fix what you have now.
  • alwaltzalwaltz Member Posts: 3
    Ah-ha. That makes more sense. I didn't know the tracks were different. I will try what you suggested before. Thanks again!
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