'Clocking' the gearcases
 

I hope this helps some people who might be confused by the terms used, or who might not even notice this could be an issue.

What is 'clocking'? Well, basically clocking means to keep a part or assembly in it's general location, but to rotate it around it's center axis. Tamiya High Lift drives often clock their transmission and transfer case to get more ground clearance. In this case, we'll clock the gearcases towards the center of the truck.

The problem:
Duratrax has the suspension geometry, for some reason or another, to have the front axle rotated forward, and the rear axle rotated rearward.
http://en.wikipedia.org/wiki/Caster_angle

http://www.playmakerstudios.com/bord...txd18a4-lg.jpg
See how the top of the servo points down towards the ground? Ideally that should be parallel with the ground, or even inclined in the other direction a bit.

The problem is that this setup forces the wheels into the ground slightly when the front wheels try to turn, which limits steering throw and puts more strain on the servo.

The solution:
The upper and lower suspension links are almost the exact same size, but not totally exact which would have made sense from an economy standpoint. To change the caster angle, you need to either move the mounting location of the upper links, move it to the center of the truck, or you need to shorten the upper links or lengthen the lower links.

In my case I went with shorter upper links because I had spare parts that would fit sitting in my workshop. The change ended up about 10mm shorter than the stock links. If I design a chassis for aftermarket production (a GOOD possibility) I would include a number of mounting positions for the suspension links.

http://i4.photobucket.com/albums/y10...5/33ad4088.jpg

If you look at my truck, the angle of the servo is tipped back about 3-5 degrees, which is a pretty neutral starting point. I used turnbuckles so I can adjust it, and when I add lower turnbuckles I can have even more adjustment built in, both for caster and the wheelbase.

Hi 3DSteve, I just yesterday lengthened the lower front links and clocked the front to a "0" degree. My question is, do I gain any benefit by giving the rear servo the same treatment? I ran the truck for a 35 minute session and noticed that I now need to alter the shock angle some, or atleast that's what it looks like.

You could do the same to the rear, the only issue is the rear axle won't slide over things as easily.


It helps to move the upper shock location in one hole when you clock the axle.

Well, only one way to know for sure; EXPERIMENT! That's the awesome thing about this hobby, you can try all kinds of things to adjust the handling and performance of your truck in just a few minutes. Keep a little notebook handy to see what each change does. I use a little set of dividers to make sure the links are always the same length. I don't even know what the specific length is, but each side matches and that's good enough for me.


Yup; clocking the axle will essentially put the lower shock mount closer to the chassis, which makes it sit more upright, makes it feel stiffer, and lifts the truck. I moved mine in two holes, just as a guess, but I like the way it sits so I'm not messing with it.