Defending World Champion Nelson Piquet of Brazil overcame a first lap crash (thanks to a complete restart) and dominated the entire weekend for his second consecutive win. Starting on pole, Piquet led from flag to flag and held off a brilliant charge by first-year driver Martin Brundle in the normally aspirated Tyrrell to win the third Detroit Grand Prix by less than a second. Brundle's car was eventually disqualified after a lengthy dispute for having illegal ballast in the water system. It was a brutal race of attrition, and only 6 cars finished.
During the initial practice sessions, as is customary on a street course, many drivers struggled to avoid the concrete walls lining the circuit. Nigel Mansell, however, immediately set the standard in his Lotus, with only Niki Lauda anywhere close. Patrick Tambay was back driving for Renault after breaking his leg at Monaco just three weeks before. American Mario Andretti, who had been called in as a possible replacement for Tambay in the race, was satisfied to spend the weekend as a spectator, watching his two sons run in the support races.
On Saturday, the track was considerably quicker as Mansell took nearly four seconds off his provisional best time from the previous day, turning a 1:42.172. His first pole position eluded him again, however, as Piquet clocked a stunning 1:40.980. Alain Prost also eclipsed Mansell with a 1:41.640 in his spare McLaren to line up alongside the Brabham on the front row. Brazilian rookie Ayrton Senna was seventh in the Toleman, just ahead of American Eddie Cheever's Alfa Romeo.
Warm and sunny weather returned on Sunday after an overnight storm had washed the track clean, but at the green light, there was immediate chaos. Mansell had decided that he could get by Piquet off the grid and aimed his Lotus for the space between the two front row cars. He struck the back of Prost's McLaren and bounced into the side of Piquet's Brabham, sending it sliding to the outside wall of the track and into Michele Alboreto's Ferrari. The right rear wheel of the Brabham was launched into the air and landed on the front of Senna's Toleman, breaking the suspension. At the same time, Marc Surer suddenly found his charge from the back of the grid blocked by Piquet's stricken car, and drove his Arrows into the Brabham's left front wheel. Taking no chances, the organizers stopped the race and made preparations for a restart.
Piquet, Alboreto and Senna took to their spare cars, but Arrows had none to offer Surer, so the Swiss was absent when the field reassembled on the grid. The second start came off without a hitch, as Piquet led from Prost and Mansell. At the end of the first lap, these three were followed by Alboreto, Cheever (having already gained three places), Derek Warwick, Elio de Angelis, Lauda, Tambay and Senna. Prost followed closely behind Piquet for the first few laps, then dropped back when his rear tires began to lose grip. As a result, Mansell closed up on the Frenchman and overtook him on Lap 10, with Piquet five seconds ahead.
Immediately, Mansell fought hard to catch the leading Brabham, taking over a second per lap off his lead. Piquet, it seemed, was driving just fast enough to stay in front, however, and Mansell was unable to get within striking distance. On Lap 17, the Lotus slowed noticeably while entering the Atwater Tunnel, as he had lost second gear. Meanwhile, not only Prost, but the Renaults of Warwick and Tambay, and then Lauda were forced to stop for new tires, while Piquet was having no trouble at all with the abrasive surface. Within moments of each other on Lap 22, Senna's right rear wheel came of in 5th gear on the main straight and he spun into the tire barrier in Turn one while under pressure from Keke Rosberg, and Cheever retired from third place with a cracked inter-cooler. Mansell finally gave up the struggle with his disintegrating gearbox on Lap 28, handing second place to Alboreto, 15 seconds behind Piquet. Elio de Angelis was a close third in the second Lotus, then a long gap back to Rosberg and the stunning Tyrrell rookies, Brundle and Stefan Bellof.
The Tyrrell team, still loyal to the normally aspirated Cosworth-Ford V8 engine, were given no chance on the season of being competitive against the mighty turbos. Already, however, they had been in the points four times in seven races, and on a tight circuit, their lighter weight and lower horsepower combined to give much better tire wear. In Detroit, this allowed them to use the softer Goodyear compound, while all the others had to use the harder compound. Also, the compactness of the cars, in comparison with the turbos, was an advantage in threading between the concrete walls, especially through the chicane leading on to the pit straight. Most importantly, Brundle and Bellof were putting in much better performances in their first year than anyone could have expected. Here, with things threatening to deteriorate at half distance, it was Brundle who would bring the race back to life.
Bellof, however, suddenly ground to a halt on Lap 34 when he struck the wall exiting the chicane before the pits. Then, just as Brundle was pitting for water ballast, Warwick set the fastest lap of the race and passed Rosberg and de Angelis on consecutive laps to take third place. About to set off after Alboreto, Warwick's Renault suddenly lost fifth gear, allowing de Angelis and Rosberg to repass him on Lap 37. His gearbox completely expired on Lap 41, and he became the eighteenth retirement of the day, leaving only eight cars still running. Rosberg succumbed next with a broken turbocharger, and when Alboreto blew his engine on Lap 50, Piquet led by more than 30 seconds.
Brundle now found himself in third place and gaining on de Angelis, who was driving without second gear in his Lotus as teammate Mansell had done before retiring. By Lap 56, Brundle had erased the ten seconds between him and the Lotus, and he passed by as they approached the chicane to take second place. With seven laps to go, Piquet was 20 seconds ahead and winding down his boost as he allowed Prost to unlap himself. Brundle continued to charge, however, taking almost five seconds per lap off the Champion's lead. Even as Brundle pulled within a second on their last entrance to the Tunnel, Piquet remained cool and took his second victory in eight days by just a few car lengths. The only remaining finishers were de Angelis, thirty seconds back; the second Brabham of Teo Fabi (scoring his first points); Prost and the Williams of Jacques Laffite.
Soon after the podium ceremony, word arrived that the officials had found impurities in the water injection system on Brundle's Tyrrell and lead balls in the rubber bag containing the water. Samples of the water were shipped to France and Texas for analysis and found to contain significant levels of hydrocarbons. Ken Tyrrell was called to a meeting of the FISA Executive Committee on July 18 and, based on the impurities in the water, which had been topped up during a pit stop, was accused of refueling the car during the race. (Refueling had been banned prior to the 1984 season and remained illegal until 1994.) The team was banned from the remainder of the World Championship and lost the 13 points they had already gained, though they continued to race, unable to score points. That was weeks later, however, and the organizers in Detroit were grateful for the stirring drive by the English rookie that was the highlight of their event.Note: Only the top five positions are included for both sets of standings. Points accurate at final declaration of results. Tyrrell and its drivers were subsequently disqualified from 1984 results and their points reallocated.