Police, Vehicle Operators and Services Agency and Northampton Borough Council staff stopped 21 private hire cabs and five Hackney carriages on 13 October.
Defects included faulty tyres and defective lights, with some vehicles found to have many problems.
Police said only 10 taxis - four Hackney Carriages and six private hire cars, were found to have no defects.
The previous check carried out in May found that only 35% of the vehicles tested had defects.
Unroadworthy cars
Insp Nigel Rickaby, of the Northamptonshire Police Road Crime Unit, said: "These are disappointing figures - we would have hoped that the private hire and Hackney carriage companies would have performed better than this.
"Clearly it is dangerous for these vehicles to be on the road because they are carrying passengers who are unaware of the condition of the vehicle.
"We will continue to carry out operations to target these companies to make sure members of the public can feel safe when they step into these vehicles."
Apart from the five cabs taken off the road straight away, three others were served with delayed prohibitions, giving the operators a specified time to carry out repairs.
Of these, faults included two defective drive-shaft joints and a defective seatbelt.
Insp Rickaby added: "In total 62% of all vehicles checked during the operation were found to have one or more defects.
He added: "19% were found to be unroadworthy and banned from operating until the necessary repairs had been carried out."
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