I installed the black shims also. My center diff trashed the silver shims after 1 race day. The were severely warped, causing the diff to bind. Set the diffs up at 20-10-5, worked great at my local track, no front tire ballooning on the straight and kept the rear from spinning out. This truggy is so easy to drive. The TKO Special bearings for the clutch bell are fantastic ! They spin like butter and last a long time. Well worth the 3 dollar price tag.