Felipe Nasr has criticised his team for yet another braking problem in 2015.
The Brazilian has complained of a recurring problem more than once this season, and now he says it affected his entire Belgian grand prix.
"I basically had only three wheels because of the completely wrong brake balance," Nasr told Globo, adding that he also had problems in Canada and Austria.
The Swiss outfit, although struggling financially, had tried to fix the issue by switching between Brembo and Carbon Industries, so it might be said now that the brake supplier can be ruled out.
Perhaps the problem is the quality of the work being carried out at Hinwil?
"I agree with everything said. It has become an unacceptable thing," Nasr told the correspondent Livio Oricchio.
Sauber technical boss Gianpaolo Dall’Ara, however, said the Swiss team has traced the problem to a "material" fault.
"Felipe used the same set of discs in free practice and qualifying," he said, "and had no difficulties."
He added: "We do not have the ability to buy 50 sets of discs, as some teams do, to see which are the best ones."
As for Nasr’s emotional post-race comments, Dall’Ara added: "When a driver sees his teammate not face the same problems and racing in front of him, it is an uncomfortable feeling."