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I have a 3435 Aquarium car that vibrates just fine, but won't revolve.

Both sprockets revolve freely, I've tried increasing and decreasing the tension on the spring with no luck.  There is a loop and a half of cord going around the drive sprocket.  Here are pictures of the unit with the film strip removed along with a video clip.

If anyone has advice on this it would be greatly appreciated


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I have the same problem on the MPC's the belt,when it stays in one position for a long time it develops a bend at the spools...I have tried to remove the bend by turning the belt inside for a might need a new belt,and remove it when the car is not used...If anybody has a fix,please let us know....joe

I also have one of these, and mine doesn't quite look like yours. To my eye, your spring doesn't appear to be stretched, but simply too long. Did you or someone else replace the spring since the last time it worked?


Admittedly, my spring as shown above has been over-stretched, but it's what I had, and it provided the proper tension to make things work!

@Chuck Sartor is correct, you clearly need more spring tension than what your video is showing. And as Chuck said, just cut a couple of loops out of the spring (preferably on the screw end) and refasten everything. Just an FYI, if your spring is too long, as yours looks to be, it can end up touching the pulley, thus cancelling any possibility of things working.

The way I adjust mine is to loosen the spring from the solder tab/screw combo, then pull on the loose end of the spring while the power is on, to see just how much tension is needed. You can, at the same time, eyeball where to cut your spring as well. Once you have found the "sweet spot", cut it where there's still enough spring left to rehook it to the solder tab/screw while maintaining the same tension, and make minor adjustments from there.

Also take note of the fact (as shown in my video) that this is a voltage dependent device; the more juice, the faster it goes. I have seen many vibrator motors that won't even move the string except when you are in a very narrow voltage band.

For those devices (and any time I work on any vibrator motor powered device) I recommend taking some 200 or even 400 grit sandpaper (I use 200 wet/dry), fold a small piece in half so that both faces have the rough side out, then stick the creased edge down into the drive pulley (remove the string first!) and gently scuff up the inner groove to allow the string to gain greater traction where it touches the pulley. It doesn't take much, and you'll see the difference right away, and it seems to last a fair amount of time before the string once again "smooths out" the inner fold of the pulley.

One more thing, my string is wrapped around the pulley only one-half turn, and it works great - frankly, I don't know if it should be 1/2 turn or 1-1/2 turns, perhaps someone else can advise?

Good Luck!



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Last edited by GeoPeg


Thanks for the very helpful insights.

The spring in my 3435 is the one that was there when received. I simply assumed it was original, as I got it from an in-law relative who was the original owner (or so I thought). Pretty sure my spring is touching the spindle, and I can see where that could cause it to short out.

I'll try un-wrapping the cord and use a half loop with a shorter spring and see what happens.

Thanks again


Thanks again for the great advice and direction!  I changed the cord from 1.5 wraps to a half wrap around the spindle.  Then I shortened the spring, and put more tension to it.  Now the spindle rotates with a fairly good amount of torque.

When assembled the function is pretty good except when the film strip comes to the point where it has been setting and has a memory bend.  I've read where some people flip the film strip inside out to alleviate this.  I wonder is this a good way? or is there a better solution?

Another thing I did.  Since these shells are painted acrylic, I think they are more fragile than some.  At the mounting hole, mine was missing a chunk and there is a hairline crack going up from it.  So I got a scrap piece of acrylic and used a fine tip on my solder iron and "welded" in some plastic to fill in what was missing and create a bond to keep the crack from opening up.  Check it out:  Not sure if I will file it to clean it up, or dremel or touch up paint or what ever to it, but I know it is more robust now for sure.


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