Hi Tankbear, :~
Sorry but this reply got a bit long...
It is well worth upgrading your tank; The metal reduction gearboxes ,metal tracks and metal drive sprockets are a must do item. They make the whole tank look and drive much better,with good grip on rough surfaces.
To answer your questions the first digit and the second digit are a sign of how the new gearbox has been 'Re-geared' So if the original gearbox is taken as 1-1 the a 3-1 gearbox will be about 1 third as fast
BUT there is a real PLUS....... although the tank is now slower there is a huge increase in Torque so that obstacles or inclines that the standard tank could not climb, the reduced gearing now allows it to climb with ease
This is not a perfect example...but think of it like your cars gearbox. Try to drive up a steep hill in 5th gear and the car will ( If you stayed in that gear) slow down and stop...but if you change down to third gear although you will not be able to go as fast on the flat you will easily be able to climb the hill. The 3-1 gearbox also make your tank move at a more 'realistic' speed ......as standard the Heng Long tanks are
WAY to fast. The 4-1 gearboxes will be even more 'Powerful' but will also be slower.
On the Forum there is a 'Gearbox Calculator' ......this is a link that takes you to a gearbox calculator download .....You can input your motor speed and gearbox reduction into the relevant part of the chart and it automatically tells you the scale speed and the 'Real' speed that your tank will do....
downloadshobbyrelatedsoftware.php
The double gears do look good BUT I cannot see the benefits as compared to the cost they will presumably last a lot longer........... BUT the 'Standard' Heng Long / Asiatam metal gearboxes are just fine, for the use that we will put them to and people have run them for hundreds of hours driving with no problems. It is, as you say recommended to 'Run them in' by using some grinding paste. Running them in will reduce the noise as the gearboxes are very noisy if you just run them straight out of the packet.....They also take much more power to turn as the gears do not mesh properly initially.
Once you have run them in you MUST remove ALL traces of the grinding compound.....and this will mean that you will have to dismantle the gearbox to clean each gear it warm soapy water using an old tooth brush or a naill brush. It is amazing how much compound can 'Hide' in the hollows of the gear casting or in hard to see places. Just split ONE gearbox at a time...take digital photos and use the other gearbox as a reference..just remember that it is a Mirror Image of what you are trying to build. Then Lube the gears with grease, motorcycle chain lube or I use car gearbox oil.....you may want to make up some covers out of clear blisterpack...it keep the lubricant that you choose from being sprayed all over the rest of the inside of the tank.
Brass or steel........I think that here it is a question of cost.....I suspect that the brass gearboxes are more expensive.....but the gears are better made and will require much less running in as you must remember that brass is
much softer than steel and you do not want to wear the gears away and so produce a sloppy gearbox.
If you are fairly good at modeling and drilling holes in the thin metal plates that hold the gears in position your could try this modification.......
Hello,
I have read on 'another forum' a very easy and simple way to convert to 3-1 gearboxes,especially if you have replaced your standard plastic gearboxes with metal ones, then you have all the parts that you need. I have recently done this conversion to my 'Good' Tiger 1 and it is absolutely brilliant ! Great speed reduction and loads more torque even on standard motors
Although you have to re-use one of your plastic gears it is at the 'top' of the drive-train and so gets very little actual load applied to it !! If its ok I will attach the link here PLEASE IGNORE THE FIRST 7 POSTS until it gets down to a guy called 'Bubbajoexx' after that it gets REALLY interesting and VERY easy to do !! http://www.rcuniverse.com/forum/m_81420 ... tm#8142064" onclick="window.open(this.href);return false;
Happy Drilling 
Alb.[/color]
This way you can just buy a 'Standard' Heng Long metal gearbox which are cheap and modify it into a 3-1 reduction gearbox at virtually NO COST....BUT, you MUST be accurate with the driling and the modification or you will just ruin the gearbox.
Sorry again that the reply is so long, but I thought that it was worth it to answer your questions properly
Alb.
hope this helps...Brian