Springs, foam spacers, O-rings, and shims after CVD upgrade

New Hampshire
Hi all,

I recently upgraded my Flux XS F-150 with the HD parts, and replaced dog bones with universal drive shafts (CVDs).
Center drive line:
#106730 - Center Universal Drive Shafts (front and rear)
#109922 - HD Cup Joint 5x10x19mm
#109923 - HD Cup Joint 5x10x15mm

Front and rear differentials to wheels:
#106709 - Universal Drive Shaft Set
#109926 - HD Diff Shaft 5x23.5mm

I've had some challenges with the universal drive keeping pressure on the 13T differential input bevel gear (101216) into the front and rear differentials, they seem to skip a lot when starting from a stop. I recall reading about HPI putting a shim/washer between the z263 pin that drives that gear and the bearing to help force the bevel gear into the diff, but can't find that thread. It's not listed in the parts diagram.

I recall small springs in my axle cups from the factory to reduce slop with the dog bones. The manuals on HPI's website for the F-150 and Vaughn Gittin Jr versions and their parts list don't have these springs, but instead list foam spacers (106889) for the front diff cups and axle cups, and O-rings (6819) for the rear diff cups. Would either of these work for the center drive cups, or would springs be best?


What works well is a little bit of fuel silicon tube cut down, I find this better than the standard small rubber black washers.

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