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Coiled Spring Pins
Application: Manual Transmission Shift Linkage Shaft/Knuckle

The designers of a shift linkage assembly for a manual transmission required a fastener to pin a shaft in a knuckle. The pin had to allow articulation of shaft and knuckle without introducing clearance between components. Clearance would result in a condition known as ‘lash’, or play in the joint. If present, this condition would be detectable when shifting. The linkage was designed for use in a high performance luxury vehicle and shifting had to be tight and responsive.

The shaft’s ball end was intended to fit within the mating knuckle. A pin would be installed through the knuckle and ball where it would function as an axle allowing rotation of the ball in a single direction. Initial plans called for a retention ring to be installed around the OD of the knuckle to prevent lateral movement, or walking of the pin within the joint. The pin would be subject to high shear load and fatigue due to torsional loading on the bar. A Coiled Spring Pin would be the best solution for use in the customers assembly. Coiled Pins are designed such that their pre-installed diameter is larger than the hole. Once installed, the pin will continually exert force within the hole. This provides positive retention and also eliminates clearance because the pin will conform to the hole wall. Recovery of the Coiled Pin in the hole will also compensate for hole wear to ensure the desired fit is maintained over the life of the application. The retention values associated with the Coiled Pin would also eliminate the need for a retaining ring.

SPIROL Engineering recommended a Heavy Duty Coiled Pin for use in this application. A Heavy Duty Coiled Pin provides sufficient flexibility to absorb shock and rapid changes in loading yet is rigid enough to limit movement thus providing excellent resistance to fatigue. Recovery of the pin in the hole provided adequate retention and the retaining ring was eliminated thereby reducing the number of parts and overall cost. Of greatest importance to the customer, ‘lash’ or clearance in the assembly was significantly reduced and this yielded the performance improvement they had been seeking.