Low whining sound from undercarriage

[Dynomite]

Originally Posted by Hib Halverson

(edited)

Gears in the early ZF S6-40s have a slightly smaller helix angle and that's why the early transmissions are a little more noisy and have a little higher input torque rating.

Regarding the ZF S6-40 ZR-1 Transmission.......I find that that the smaller helix angle (of the gear teath) attributing to a little more noise and higher input torque rating is of technical interest and worth documenting........something not described before

[Hib Halverson]

Originally Posted by Dynomite

(snip)something not described before

The change was made mid-year 1993, as I recall. Without trying to find some of my old S6-40 articles I can't say for sure. Graham remembers more about that change than I, so maybe he can confirm the time line.

The early S6-40s were designed when GM was still considering a turbocharged LT5 for the future and it wanted some extra torque capacity. After it became obvious there never would be an LT5TT, GM decided to address customer complaints about noise and decided to increase the helix angle as well as the other changes Graham details. The decision resulted in the later transmissions which were quieter and made less noise.