My way of tightening up the steering is a little more complicated and time consuming but there is no freeplay or wobble in any of my trucks and people I have done the conversion for.
Firstly replace the servo as in most cases they are a standard type, I use digital - metal geared - with a stall torque of 16kg at 6.0v, lots of grunt!
Throw away Tamiya's nightmare called a servo saver, should be renamed to a steering crippler!
I use an aluminium servo horn tapped at 3mm and this one is held to the servo with a 3mm screw with a dab of contact cement to prevent it coming loose (threadlock is good but bloody hard to undo).
Next replace the ball joints on the arm that links the two steering knuckles.
I use a 3mm tie rod end and a 3mm bolt. You have to keep undoing one of them to align the wheels (I did say time consuming?).
I then drill out the plastic connectors (the bit that fits over the the ball) to 5.00mm and use two 5 mm shoulder screws (Traxxas Part) and bolt one end to the servo arm. with the shoulder bolt inserted in the knuckle end you can then align your steering. Once happy screw the shoulder bolt into its nut on the other side.
While this works quite well for the Tamiya front axle and knuckles, I still was not entirely happy with the outcome so if you want to improve on this idea try adding in the following items.
These are examples only and they can be bought from quite a few vendors.
Replacement axle, these use nylon bushes to support the pin:
http://www.ebay.com.au/itm/ALUMINUM-...item2a1cc44fc9
And these are the knuckle I use, nice smooth snug fit:
http://www.ebay.com.au/itm/ALLOY-ALU...item19c8b005a1
Hope you find this helpful.