So how about this: productivity in any specific labor process of capital, the substitution of machinery for labor, the "real subsumption of labor by capital" does not automatically generate the expansion of relative surplus value. Socially, in the production process, this real subsumption amounts to valorization of greater increments of capital by lower increments of labor power.
Regarding the valorization process, however, the increment of valorization is magnified not by the depreciation of the value of the wage, not by the the reduction in production time alone, but in the reduction of turnover time-- shrinking the lag between production and realization, reducing the gap between production and circulation, such that capital recuperates its "advanced" outlay more quickly, and recirculates that recuperation such that its subsequent outlays for "v" and "c" are paid for, more or less, with "house money," requiring no following "original" outlays.
Now as Marx makes clear in the Grundrissee and the other Economic Manuscripts, the very mechanisms that reduce turnover times for portions of the total capital-- the investments in fixed assets which only transfer their value in fractions-- also entail the slowdown in the turnover of the entire capital. Thus while the investment in fixed assets only participates incrementally in the valorization process, the entire investment is required to participate in the labor process.
EDIT: So that capital expansions are (almost always) initially indicated by expanded and expanding investments in the means of communication and the means of transportation. "Telephones and trucks" used to be the phrase used on Wall Street to identify the "upticks." And... at the same time, the investment in these assets, these improved, more efficient, better performing assets, entails a slowdown in the realization of their value-- something made so painfully evident in the overproduction of container ships, with total capacity doubling between 2013 and 2016, revenue per container at record lows, having declined 25% since 2015, and the adaptation of "slow steaming" techniques to keep the fleet in service and avoid the "downtime" and costs of laying the ships up.
Said an official of the Maersk group, referring to the automated container terminal Maersk operates in Rotterdam, "It takes a long time to realize the returns."
The comrade at theplanningmotive.com has explored this. And I'll be rereading volume 2, just to see how much I'm fooling myself.
July 7, 2016
Here and here