2

I have a push and go motor, also known as Hub No5 model also known as engine base part #28743

The issue I have is that the train can not climb the bridge anymore, unless using the locomotive alone and also stops in curves. After looking carefully I noticed that one of the wheels was slipping.

When I take it in my hand upside down, make the front wheels rotate (the one with the sensors), the propulsion wheels starts rotating. At that moment, if I try to slow down one of them with my finger, I feel it generate torque. For the other one, it just stops easily and I feel the wheel axis continuing to rotate. And I feel some steps.

With the help of the thread How to disassemble LEGO train engine base part #28743 I managed to disassemble nearly everything.

Now, I would like to remove the wheel from it's axis to see what is "broken" inside, and hopefully with the help of a 3D printer, rebuild the broken part.

Any idea how to unmount that ? Is it simple "press fit" (I don't know the exact english name for that).

EDIT

I have to precise two things.

  1. The batteries are fully charged so it's not an issue
  2. I have two locomotive #28743 and one of them has an issue. I really feel something broken in the "wheel", the wheel is loose from the gear and can rotate nearly freely. So it's not some kind of a kid protection you really feel something is broken inside and that's why I wanted to know how to disassemble the wheel.

enter image description here

  • 2
    Cannot really help you with disassembly. However, to reach you final goal - get a working train base - you may just get in touch with LEGO Customer Service to replace the broken item. They are pretty good at dealing with such issues. – Alex Mar 22 at 19:42
4

My back wheels do the same thing. There is no metal axle that connects both back wheels like the axle design does for the front wheels, but I'm sure LEGO designed it that way.

So, imagine the train's motor being in an "ON" state just a rolling. Now enters a kid, just being a kid. Grabs the thing, and starts a rolling in whichever direction kiddie wants to roll. Not a caring that the motor is doing it's own thing too. How does LEGO protect the device from the free rolling madness of a child?

So, I think this slippage is a built in feature to kid proof protect the motor from being over torqued. Some type of reverse rocket booster dampening system. Analogous maybe to a circuit breaker which, is an automatic device for stopping the flow of current in an electric circuit as a safety measure.

Possible solutions:

(01) Battery check. You said it no longer can pull extra weight, and that it stalls even on flat normal gravity leveled curves? Huh? So, before we go too deep, I would recommend first replacing the batteries with new ones. Then, retest it.

(02) Balancing our time vs. the money justification check. Tearing down the housing to get inner access to remove excess hair and debris from this unit is fairly easy, and just requires buying a T9 Star Torque from the local hardware store and maybe 15 mins of our time.

Even though this thing is LEGO engineered like a tank, we can still imagining extensive damage, let's say a smoosh over by car, where we'd need to replace the circuit board, motor, or destroyed plastic gears.

Then, maybe it might be time to do a price check and consider purchasing a new/used unit versus the time to invest and produce a 3D printed replacement.

(03) Axle wheel hub tear down (setup only). I'm not taking mine apart, becasue I haven't justified a reason that works out for me, but this is my observational approach if anyone else wants to venture further into the unknown.

So, let's look at the wheel design and note the similarities/differences between both wheel hubs.

enter image description here

enter image description here

Break down wheel hub anatomy consists of at least three pieces.

  1. Inside hub piece.
  2. In between trans-clear rubber tire tread.
  3. Outside hub piece.
  4. Unknown non-visible pieces. Possible notched out axle bar.

The inside hub pieces and in between trans-clear tire tread all look to be the same molds, where the outside hub pieces differ in aesthetic design, but function in the same way when interlocking with the inside hub piece.

Here's where things get dicey. There seems to be six interlocking tabs that need to be simultaneously unhitched to separate the pieces without permanent damage. Unless you happen to be a six clawed mutant named Wolverine, this will be a challenge.

enter image description here

Six interlocking tabs release damage free setup and approach:

  1. Hot glue one end to work desk for stability.
  2. Insert six flat head precision screwdrivers.
  3. Wiggle until it's free.

Six interlocking tabs release egg breaking, omelette making approach: Goal: 3D print a replacement, so permanent damage doesn't matter.

  1. Using a Dremel rotary tool, carefully drill out 4 of the 6 interlocking tabs ONLY. Don't go deep. We can 3D print plastic, but not the clear-trans rubber treading.
  2. Insert two flat head precision screwdrivers to disengage the locking function of the 2 remaining tabs.
  3. Using a digital caliper measure out the dimensions of the working 2 remaining tabs.
  4. 3D print replacement piece.
  5. Consider using some Loc-Tite glue adhesive when reassembling the wheel hubs.
| improve this answer | |
  • 1
    I have done an EDIT. Beside thanking you for the details answer I would like to precise a few things. First of all I totally agree with you for the time vs price. But in my case my son has two locomotives and with the coronavirus and curfew it was a game disassembling, asking question on stack exchange, waiting and answer and eventually building something with a 3D printer. Moreover here I cannot buy the part #28743 alone. And I would prefer to keep the 50 bucks of the duplo train box to buy the "real" lego train when my kid grow up. – HpTerm Mar 23 at 20:08
  • 1
    Also, as I said in the edit, when I compare the two locomotive, I really feel something broken and the axle of the gear rotating independently from the wheel, even in simple curves with nearly no low. We did slow motion vids with my son trying to figure out the issue. So beside all that game thing making time past quick in those hard times needing to stay home, I would like to thank you for the detailed answer as well as you "funny" way of describing things ... no, nobody in my family has Wolverine like hands. – HpTerm Mar 23 at 20:12
  • Hey, Friend, I've read your edits, and I believe you on the breakage 👍🏿 👌🏿. Don't know where you are in the world, but for me a used set runs $16 bucks, where as the part itself alone is more expensive. Go figure... My job is part of the supply chain, so there's no forced play time for me. So, unless I get the "Captain Trips"... – Rin Rio-Oki Mar 24 at 3:47
  • ...but, I am still curious on how to unhitch the six locks without destroying the thing. (I kinda like mine...) If I had two like you, and one train was already broken, plus the equipment/time to replicate a replacement, I definitely would be doing some exploratory dentistry with the Dremel. LOL, Wolverine like "hands"? Claws, Bub! ;) – Rin Rio-Oki Mar 24 at 3:47
  • 1
    I'm in the United States. That price is bonkers! Yup, that money could be put toward something more prudent. Well, anyway, if you're able to pull off some kind of breakdown, any kind of breakdown, please feel free to share your knowledge with all of us here. See ya ✌ – Rin Rio-Oki Mar 24 at 12:50
1

FOLLOW UP POSTED AS AN ANSWER

So, I managed to disassemble the wheel axle from the gear axle, which show what I was expecting, a broken piece in the freewheel.

As my question is on how to disassemble the wheel itself @Rin Rio-Oki answer is the correct one.

A picture is worth a thousand words so put picture ...

The wheel axle is simply force in the gear axle, so simply by pulling firmly but carefully disassemble both.

The small teeth in the wheel axle interact with the 4 white teeth of the gear axle to create a freewheel, and that's one of those that is broken in my case and that explain the slipping.

Note that I don't know what could have caused that teeth to get broken.

enter image description here enter image description here enter image description here enter image description here enter image description here

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.