Not much! Contrary to what you may have been expecting and what some American hawks were advocating in the 1980s, during the pre-Tiananmen era the Chinese did not go on a shopping spree and stock up on ready-to-use American weapons and platforms. Rather, the acquisitions focused on cost-effective upgrades to existing capabilities, advanced (if not quite cutting-edge) technologies that the Chinese defense industry could adapt, and a few specific purchases of utility and transport aircraft.

So starting in 1980, the United States allowed sales of military equipment to China, reversing prior policy. Initially these sales were limited to non-lethal civilian-military (or "dual-use") items such as utility and transport aircraft, trucks, and communications equipment--arguably not "arms" at all. In 1981, the policy of refusing all arms exports to China was negated and in 1983 China was allowed to purchase higher technology dual-use items. In 1984-85, the Department of Defense agreed to some Foreign Military Sales programs for China in addition to the commercial sales that had been going on.

The most notable completed transactions were the 1985 commercial sale of 24 Sikorsky S-70C helicopters (civilian equivalent of UH-60 Blackhawk) and the sale of a batch of GE LM2500 naval gas turbines which were installed as the powerplant of a Type 052 destroyer. There were some smaller purchases of utility and transport helicopters such as Bell 206 JetRangers and Learjets.

Transactions interrupted by the post-Tiananmen embargo include a major avionics upgrade to China's J-8 fighter fleet which would have brought these aircraft derived from the Soviet MiG-21 up to about late 1970s-early 1980s technology. This was an FMS-facilitated program that involved Grumman and Westinghouse and would have been worth about half a billion dollars had it not been cut short. There was also an FMS-facilitated program to build a modern munitions plant, and others for artillery radars and radios and antisubmarine torpedoes.

Transactions proposed by Western commentators but not consummated included large-scale sales and license production of American missiles such as the TOW antitank missile. As far as I can tell, this was not something the Chinese wanted; rather the Reagan administration and defense contractors wanted the Chinese to buy them.

For China did not want simply to be a buyer of American arms, impoverishing itself and enriching American defense contractors. Keep in mind that defense spending, particularly on imports, had low fairly priority in China's budgets during the 1980s. This was the era of Deng Xiaoping and the Four Modernizations (agriculture, industry, defense, and science & technology) which were aimed at increasing Chinese self-reliance. Although defense was one of the Modernizations, the government did not want to spend a lot of money buying American, particularly when American arms were so expensive. In addition, China had a long history of favoring a comparatively low-technology "People's War" strategy. Rather, the idea was to make highly selective "more bang for the buck" purchases that would help develop the Chinese defense industry and supporting technological developments. Keep in mind also that other Western countries were selling to China at this time, notably France, Great Britain, and Italy. Possibly China's costliest, most consequential, and most disappointing defense acquisition during this era was a program to license-build Rolls Royce Spey jet engines (to be used in what became the JH-7) that began in 1975 and was still plagued by problems in 1989 (and for years afterward).

To be sure, reluctance about large-scale arms and defense technology transfers came from both sides. In the 1980s, the United States government considered China a potential counterweight to the Soviet Union but certainly not an ally. There was concern, particularly in Congress, that China might behave aggressively toward Taiwan, which is probably part of why the programs actually undertaken were more defensive in orientation.

The post-Tiananmen embargo ended these relationships and forced China to rely more on itself, which of course was not incompatible with the prior defense acquisitions strategy. The Chinese government had never wanted to be a bulk importer of American weapons, and now it couldn't be one. With respect to advanced technology, during the 1990s there were leaks and espionage, evasion of the embargo by some companies from Western countries that had ostensibly banned further defense export, and closer cooperation between China and Israel. The Israeli military and defense industry had many advanced Western technologies but was not subject to an embargo regime. E.g., China's J-10 fighter developed during the 1990s was believed by many to incorporate technologies from the Israeli Aircraft Industries Lavi fighter project of the 1980s.