Shivvers Manufacturing Recalls Lawn Mower Jacks Due to Collapse Hazard. Hazard: The jack lifts can have threads stripping or the nuts breaking, resulting in the shaft slipping and the mower falling from its stand-up position. This could cause serious personal injury to the consumer or property damage. Incidents/Injuries: Shivvers has received five reports of jack lift failures and 37 warranty claims for replacement parts. Description: The recalled jacks are used for lifting the lawn mower during service or maintenance. Two versions of this jack model have been manufactured. Version number one was made with a nylon nut and version number two was made with a sintered bronze nut. These recalled jacks were sold separately and on Charger, JAZee and Boss riding lawn mowers.