DETROIT — The deeper General Motors digs into its vast portfolio of vehicles, the more safety problems it finds.

The announcement on Monday that G.M. would recall another 8.4 million cars and trucks for a range of defects appears to be a direct result of the company’s newfound vigilance to rooting out safety issues.

But even as G.M. addresses its safety shortcomings with a beefed-up roster of product investigators, the spiraling number of new recalls — G.M. has surpassed 29 million worldwide this year — is threatening to undermine the company’s reputation for quality.

“We’re hitting unprecedented numbers and it’s reasonable for people to start asking, When and where will it end?” said Karl Brauer, an analyst with the research firm Kelley Blue Book.