Quote:
Originally Posted by gbrtng
Agreed ... and the tranny does NOT have straight-cut gears ... where did that idea come from?
TGF
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U R correct, Glenn.
Doing some research on the ZF for a possible article in the HOTB, I came across some facts from reliable (ZF manufacture's docs and ZF mechanics), as well as the (many repeated?) myths, e.g., the "straight cut gear".
For anyone curious, this is what I've found so far...
Black vs. Blue tag'ed units essentially only denote where the units originated from.
Black tag denotes those units which originally were built/supplied by
Germany. Later, when GM attained the rights to build them in the US (Vernon Hills, IL), those units have the
BLUE ID tag attached to the case, denoting
their origin is the USA, including warranty work on all of the ZF transmissions used in the ZR-1.
In all there were 6 different iterations of the ZF used in the ZR-1 during the 1990 thru the 1995 production, but these are grouped into two major differences: The 610Nm units and the 540Nm units.
With exception of reverse gear,
BOTH the 610 and the 540 ZF have helical cut gears.
Some background: "Straight" gear cut is where the cut is parallel with the axis of the gear. Straight cut gears have the advantage of
zero lateral thrust as the force is at right angles to the teeth of the gear.
Helical cut gears' teeth are cut at an angle to the gear axis. The advantage is the gears run quieter, especially noticed as speed increases.
However there is a trade-off: helical cut gears also produce some amount of lateral thrust as the force is at an angle to the face of the teeth. When it comes to handling torque, often the limiting factor is the transmission's case's ability to stay together under the lateral forces developed by the helical gears.
The greater the angle, the less whine. The angle of the ZF gears was increased to mitigate some complaints about gear whine in the "610" ZF. However the trade-off was the torque rating: the increased angle reduced the gear whine, but also increased lateral thrust. Thus, the rating was reduced from 610Nm to 540Nm (approx. 450 pounds torque rating reduced to to 400 pounds, respectively).
Photos:
A cut-away of a ZF - just which version, was not available (610 vs. 540). Note the helical cut gears.
A good example of the differences in the gear cut angles and the advantages and disadvantages is the Muncie M21 and the famous M22
"Rock Crusher" (The rock crusher name was given to it because of the gear noise resulting from the shallower helix cut - that racers happily accepted in exchange for the strength.)