You see the cap was increasing even before Reagan, although it was flat from 1937-1950.
The real value of the cap in 2013 dollars increased from $73,165 in 1980 to $88,544 in 1988, but it was also growing before Reagan, being just $62,324 in 1974.
The real thing Reagan did was increase the payroll tax, it was 6.13% in 1980 and 7.65% by 1990 (although some of those increases may have come from laws passed before Reagan was President) and the tax increase on the self-employed was huge. Those job creators saw their tax rate go from 8.1% in 1980 to 15.3% by 1990, almost a 90% increase, and on top of the increases in the cap. http://www.ssa.gov/oact/progdata/taxRates.html