I donít see the purpose of that coupler. Yes then you can put a 23 spline tcase input in, but the trans output is still 21 spline. So you havenít strengthened anything, just moved the weak link from the tcase input to the trans output. And Iíd rather break a tcase input any day over a trans output.
I think more importantly, the t-case input sees at least 2.28x less torque than the t-case output when in low range. You need the 23-spline more at the t-case output thought my wimpy 21-spline stuff has been doing just fine with my high output (my 4Runner is lifted) big horsepower (singular) engine.
1989 4Runner: Dual Ultimate (Inchworm front & Marlin 4.70 rear), Marlin Twin Stick, 1200-lb clutch, 4.88 R&P, Aussie Front, Detroit rear, 30-spline Longs, Long hub gears, ARP hub and knuckle studs & 35x12.50 Cooper STT PRO tires. Marlin rear bumper & sliders. FROR front bumper. SAS with Alcan springs & Rancho 9000XL shocks. Budbuilt Bolt-on traction bar. Custom Interior Cage by Those Guys Rod and Customs.
Moab Tested & Rubicon Approved