What defines a straight-cut gearbox
In straight-cut gearing the teeth run parallel to the gearbox axis. The decisive consequence is that no axial force is produced. The load acts purely in the circumferential direction, the bearings have nothing to absorb lengthwise, and the arrangement stays correspondingly simple.
The price is the noise level. Because only one pair of teeth is ever in mesh, power transmission begins and ends abruptly across the full width of the tooth. That periodic excitation is audible — it is the characteristic singing note known from motorsport. It is a property of the design, not a sign of damage.
Where straight-cut gearing has its strengths
Three properties make it attractive for competition use:
Efficiency
Without axial force there is less friction in the bearings. What is not lost as heat remains available at the wheel.Robustness
The simpler direction of load makes the assembly less sensitive to the peak loads that occur in racing.Package
The gearing is shorter in build, which matters with closely stacked gear sets.
Helical gearing reverses the trade-off: several teeth in overlapping mesh, a markedly quieter run, higher load capacity for the same size — at the cost of the axial force, which has to be absorbed by suitable bearings. For a road car that is almost always the right choice. In racing, efficiency and robustness come before refinement, and that is why straight-cut gearing is still used there today.
How we produce gear sets
We manufacture straight-cut gear sets for historic Porsche motorsport on our own gear-cutting machines — among others for the gearboxes of the 904, 906, 908 and 917.
The finishing operation is what matters: our gearing is ground, not lapped. Grinding achieves a tolerance of 0.0025 mm and a reproducible tooth contact pattern — with lapping, both depend on the mating part. Every set is individually numbered and supplied with an inspection record, so the geometry stays documented and traceable.
Gear sets for the common motorsport types are held in stock. For everything else we produce to drawing or from an original part as a pattern — send us the documents or the old part and we will tell you what is feasible.