diff shims?

[yamabraaaper]

I have a tmaxx 4907 I'm the third owner and it either has a rear diff lock or something is wrong with it. Any pros and cons to the diff lock are appreciated. What is the point of a diff lock (I know what it does I dont understand why its beneficial). And I've seen alot of posts about diff shims but I dont understand how you shim it and what to look for when shimming. Thanks in advance
-christian

 

[ThunderTiger]

Diff shims change the depth of engagement between the input pinon and the internal star gears. Too deep in mesh and the diff runs tight with high gear wear, too little mesh and you risk sheering/stripping teeth.

As for spools, a bad idea and something to be avoided. Only benefit, if you can call it that, is that power is delivered equally to both wheels even if one wheel has no grip or is in the air.

far better to fill the diff with the thickest possible diff oil and have an LSD (Limited Slip Differential) as a result.

 

[Nitro4910]

Spools are hard on the drivetrain components, for a real stiff LSD type action, you can use plumbers putty in the rear diff, it's thick but still has some give.
I run it in all my rear diffs, and you can can get a tub of it from HomeDepot for about $2.