...how low the Yuan needs to upvalue in order to affect the U.S. Chinese trade deficit? And how long will it take to get the correct currency ratio? What will happen during this time? The authoritarian leadership stops the process in evidence of slowing economy and or a rise in unemployment?  Will it happen at all?...

Us Dollar (USD) /Chinese Yuan(CNY) rate: 6.3, do we really want to devalue the relations?
We are witnessing years of accumulating huge stock of dollars and dollar-related assets such as U.S. bonds, as a result of U.S. imports and investments in China.  Lot more Chinese workers have jobs and increasingly paying higher wages.
The value of the dollar is established in the world's money markets supply and demand. In contrast, the Chinese Yuan's exchange rate is effectively dollar-linked by the Chinese government, meaning, the Chinese currency is not a subject to supply and demand  and in light of the tremendous surplus and rising wages, the Chinese currency needs to devaluate significantly in relation to the USD and the rest of the world.  Economists urged U.S. politicians to call on China to revalue the Chinese Yuan, ratiocinating that expensive Chinese products will lead to imports reduction thus reducing the U.S. trade deficit at the same time, reducing the stream of funds to the Chinese manufacturers and more for the United States producers to create jobs desperately needed and increase tax revenues to pay outrageously growing budget deficit. A response came from in the past year to the U.S. political pressure by allowing the Yuan to a mild appreciation against the dollar.
It is surely understandable in terms of pure academic analysis, on ways to stable trade balance, but is it right in this case of dealing with communist rulers that can change any strict policy in a matter of days and a huge gap of wages between the U.S. worker and the Chinese one. In that case, how low the Yuan needs to be devaluated in order to affect the U.S. Chinese trade deficit? And how long will it take to get the correct currency ratio? What will happen during this time? The authoritarian leadership stops the process in evidence of slowing economy and or a rise in unemployment?  Will it happen at all?

However, in this sort chain of events, initially the U.S. balance of payments will get worse simply by paying more money for the same products. Revaluating the Yuan may implicate a situation where U.S. importers will impose higher prices on the consumers and keeping their small margins. Higher consumer prices leads to inflations or in the current U.S economy fragile condition will lead to even stagflation. Stagflation is a period characterized by an increase in unemployment and a decrease in economic development and growth.