MMM Restoration - the Uni-Tred by Claude Hanssens

Disassembled Unitred "Guts"

Submitted by Claude Hanssens, Brussels, Belgium (non English) on 2020.01.13

A few weeks ago, I bought a Uni-Tred + Space Bubble package on E-Bay.

Unfortunately, the Uni-Tred was not functioning: when switched on, it produced a horrible creepy sound and refuse to go forward. I decided to fix it.

By design, the Uni-Tred is fully sealed by glue: no screw. I carefully open it using a combination of tools: stiletto with various blades, screwdriver,…

I managed to separate most of the seals, but I also had to cut through some of them. Because most of the seals are under the track, when rebuilt, it will be invisible.

The Uni-Tred gear

As in the Space Crawler, Mattel put in the Uni-Tred an advanced gear system.

When advancing on a horizontal surface, the Uni-Tred goes full speed. On steep slope, it automatically switches to a lower speed with greater power.

Here is a description of the functioning of the gear.

Here above you see a picture of the engine and the gear system.

3D drawing of the gear

Basic function:  
  1. Engine (grey + white wheel) turns the purple wheel; 
  2. The purple wheel turns the tallow wheel; 
  3. The yellow wheel turns the orange wheel (large wheel).
    Till now, this reduce the speed of the engine. 
  4. The orange wheel turns the light green and blue wheels. 
  5. The blue wheel turns (loose connection) the light green wheel. 
  6. The light green wheel is connected to dark green wheels that turn the track. 
The orange wheel has 3 parts
  1. Large connected to the yellow wheel 
  2. Medium (n° 1) connected to the light green wheel (n° 3) 
  3. Small (n° 2) connected to the blue wheel (n° 4). 
Medium orange wheel (n° 1) has 24 teeth. Light green wheel (n° 3) has 18 teeth. One rotation of the orange wheel produce 24/18 = one and a third rotation for the light green wheel (n° 3). 
Small orange wheel (n° 2) has 10 teeth. Blue wheel (n° 4) has 32 teeth. One rotation of the orange wheel produce 10/32 = a third of a rotation for the blue wheel (n° 4). 
A spring pushes the blue and light green wheels back in place. 
On horizontal surface: 
On horizontal surface, the light green wheel turns faster (1+1/3) than the blue wheel. A loose connection (a differential made of a light slope on the rotation direction) makes “jump” the blue wheel. It produces the sound “Tac Tac Tac”. The Uni-Tred goes full speed. 
On slope:  
The track “brakes” the dark green wheels. The result is that the light green wheel is pushed away from the left dark green wheel. The light green is disconnected from the orange wheel, as show manually here under.

Now the orange wheel (small part N° 2) turns only the blue wheel. 
The blue wheel (n° 4) turns the light green wheel (n° 3). The differential has a connection in the direction of rotation. The Uni-Tred slows down but at full power. 
I made 2 videos with each function. 

Matt Mason – Filling gaps 

There is sometimes needed to fill gaps in your Matt mason stuff: melt down by contact with a soft plastic, big scratches, or to fill gaps when you opened your Uni-tred. 
Modelers use the following tip: You can use the small parts of your Uni-Tred, broken when you opened it.
You can also use sprue of model kits (ask a modeler friend). You can find them in various colors. 
Styrene Model Kit Sprue
  1. Cut the plastic in small parts (a few millimeter long). 
  2. Put the parts in a glass jar with of top. 
  3. Add Cellulose thinner (to almost cover the plastic). 
  4. Close and wait. 

The plastic will melt down to form a paste. The more thinner you added, the more liquid the paste will be. You have to experiment. 

Use this paste to fill gaps, scratches, … It will harden in a few hours – a day. You can then sand, polish, …


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