TH125 Capabilities (Page 2/2) theogre FEB 02, 12:36 PM Auto Trans Torque rating is On the Input Shaft. TH125c also know as 3T40 is one of the Weakest auto trans GM made & rated ~ 200 ftlb. Torque Converter puts ~ 1.5 to 1.8 or ever more X Engine Torque & w/ "big" engine will easily overload the trans. If Engine puts out 150ftlb X 1.5 = 225ftlb, X 1.8 = 270ftlb, in to TH125c rated ~ 200ftlb Worse, TH125 have different parts internally over the years made & more... Examples: units for Dukes may have different clutch packs etc vs units for V6. later units have bigger chain & sprockets regardless. So saying the unit will work w/ whatever motor is often just luck even when someone have this unit "behind" that motor... And This is Common for Auto Trans & not just GM. Ford C4 had many changes for given motor attach to them. Including 1 piston pack to drive one clutch pack had different sizes & had Letter on it to tell from outside which piston set you have in a car. "Code" A for Small Block V8, other letters for L6 etc.