Belarus 400-series 4x4 (420A, 420 AN, 425A, 425AN, T42LB, T40A, T40AM) Semi-Flexible Driveshaft Coupling Donut
The four front diff bolts on my 420A were loosening under heavy loader use and putting extra stress on the diff input shaft flange & driveshaft flange. I upgraded to stronger fine-thread diff bolts and made a semi-flexible driveshaft coupling donut to help absorb potential stresses.
For the donut I used 1/2" HDP (High Density Polyethylene) aka Starboard/Seaboard but an old poly cutting board will do the trick. Anywhere from 1/4" -1/2" thick x about 85 mm dia. The ft diff input shaft floats fore & aft so if you have the 39-1/2" long OEM driveshaft (Part #: Т40А-2302072)
up to 3/4" can be added to that. I only used one 1/2" thick donut between the front flanges but one could install, i.e., two 3/8" thick donuts, one on each driveshaft end.
I used 7/16" (double-nutted) bolts as they're a tight fit & help align the shafts. Note pictured bulge after tightening flange bolts.