Identify the type of intermediate clutch outer race in use. There are early and late design races. The early design race was used in all 1964 to 1976 models, and can easily be identified by 47 splines around its outside diameter, with four spaced lube holes drilled along the center-line of the void between adjacent splines. See Figure A. The late design race was used in all 1977 and up models, and can easily be identified by 43 splines around its outside diameter, with four spaced lube holes drilled along the center-line of the omitted splines. See Figure B.
The early race was manufactured from specialized steel billet blanks, a perfect match for the high powered vehicles of the 1960’s and early 1970’s. The late race was manufactured from a hydro-formed steel based composite material as a method of cost savings, better suited for lower powered smog era vehicles.
Note that no service bulletins were ever released by General Motors in regards to the manufacturing/materials change. The original engineering blueprints provide the only testimony of this production change.
Close inspection of hundreds of races over the years has revealed that due to the materials used to manufacture the late design intermediate clutch outer race, it suffers from elastic deformation under a load as well as increased wear at the sprag element work surface. This severely compromises the performance and durability of the intermediate sprag assembly in high load applications, encouraging “rolling” or “flipping” of the sprag elements. In all drag race and high load applications, always upgrade to the early design intermediate clutch outer race. CK Performance products has taken the performance and durability advantage of the early design intermediate clutch outer race one step further by offering a fully inspected, specially stress relieved and black oxide coated version of this factory performance part, making it an excellent choice for all high output GM TH400 applications which utilize a 34 element intermediate sprag assembly. It is available under part # 4CC/HDICOR34.