Brakes lockup if pushrod length doesn't have expansion clearance. Even new OEM product can have 40-60 thousandths difference.
Master cylinder was leaking internally and loosing pressure. Not good for mountain driving.
Was on a trip 500miles from home and no tools. 2weeks before any shop could look at it. Yuk Went to auto parts and bought new master cylinder, bench bled, measured for correct rod length, all ok.
After install bled brakes, ok Drove 1/2mile and brakes totally locked up.Had to have towed to hotel.
Decided to try something temporary. Loosened the 2 nuts holding cyl.to booster, then used cardboard to shim it out about .60 and tightened nuts.
Problem solved, enough to get us back home 500 miles ,where proper repair can be made. The rod length needs to be shortened and now with proper tools and location, it's not a big deal. Not 1 mechanic offered that seniaro.

 

Shimming the master is a stroke of genius; thinking outside the box.
A retail mechanic thinks in terms of flat rate and safety. They would not do this to a customers car for fear of legal repercussions in the event of an accident...liability issues.
Good solution to and unusual problem however.

Mcgiver would have done it .
Did you mean 0.060"