For the tracks:
1.) Steel portions - gun metal / rubber blocks - flat black
2.) First wash - thinned flat earth + dark brown
3.) Drybrush steel portions - metallic grey then chrome silver (just lightly)
rubber blocks - grey
4.) 2nd wash - thinned buff
5.) Dust coat - light spray coat of buff
Panel lines: Pastel chalk - black
However, preshading is also a good way to achieve this. I recently did a desert sherman and I did not use pastel chalk. I just preshaded it using desert yellow + flat black. Here is what it looked like:
http://www.geocities.com/ddta_ala/M51_sherman