I just ordered the Blackwell axles earlier this wk, never had them before. The 3.75 ratio looks appealing for use with larger diameter tires. What Lmack was saying to lock an axle is for the axles that come with the trk kit, these blackwells I'm not sure if they even have a differential in them... I lyk when they show up in a few wks.
I also got these servo lockable axles in the order to try out as well, see if they can take the long term heavy pulling better than the current stock trk axles.
http://store.rc4wd.com/Scale-Semi-Tr...al_p_2891.html
I usually lock the rearmost axle & leave the rest open. Locking them all would eventually cause a lot of problems, especially if trk was loaded down most of the time. Shoe Goo added to the inside of differential works pretty good for a limited slip action, and I add it to the front powered steer axle.
The stock trk springs don't carry much weight before the frame is resting on the axles, although that doesn't seem affect articulation of the axles too much through uneven terrain.