The Hunter's fleet of electric delivery vehicles was returned to the region in time for what Australia Post expected to be a record-breaking day for parcel deliveries.
The postal service withdrew its electric delivery vehicles or "eDVs" across the country a fortnight ago due to safety concerns.
The Hunter currently has the highest density of the vehicles out of any region.
Australia Post said it took the three-wheel vehicles off the road due to concerns about its front axle. The Communications Electrical and Plumbing Union said the axle had collapsed on three of the scooters in Ingleburn the week prior.
At the time of the withdrawal, up to 129 scooters were in use in the Hunter of a total 320 scooters in use across the country.
An Australia Post spokesperson said the axle had been replaced in the 113 vehicles it had returned to the Hunter by Monday.
"We engaged experts, including safety engineers, to investigate the issue and following recommendations the manufacturer has begun retrofitting our entire fleet of eDVs with new axles," he said.
In a letter to its members on Friday, the NSW CEPU branch said Australia Post's process had found a defect in the front axle "related to incorrect heat treatment specification". It said the new axle design had undergone a number of checks, including one conducted by an "independent heat laboratory". The entire fleet would be retrofitted over the next month, it said.
Australia Post was expecting to deliver more than three-million parcels on Monday.
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