I went to check torque on my -7 spar bolts and the wrench did not click and the calibrated arm said stop
This is posted as this wrench is new from 1973 and has been checked for calibration along the way as good. It has a soft metal, like lead, plug in the bottom that prevents disassembly, so this is to show it can be done and the inside after several years of professional use and decades of home use is still in good working order. The plug is most easily machined out. It has hidden washers inside to thwart drilling. There are two steel washers and an internal plate to prevent access from the other end.
I cleaned all and calibrated using an electronic torque meter. It has two adjustments. One for the main spring that determines the zero or 150 ft-lb intercept and another under the rocker pivot that adjusts slope. My end calibration result was .5% overall and no more than .7% max from 20 to 140 ft-lb.
MAC will not
service this tool. The mechanism is different than the CDI type with the square rocker. In the CDI the rockers must be physically be replaced. In this tool the pivot adjustment takes care of the slope.
These wrenches were made for a long period, and are available on xbay around $100. I would offer less due to the fact they have the tamper proof plug and no where on the internet was a take-apart found.
Use superlube with PTFE for the lubricant on all the parts. It is what CDI recommends.
One caveat, when unloading the tool for storage, NOT NOT BACK lower than zero. The lever fork will allow the rocker to unseat and the wrench will not function correctly. This was my original problem - self inflicted.
If you get one of these they are strong accurate and reliable. Don't back the handle out too far! I will be happy to provide guidance of you want to calibrate. I have numbers for the slope adjustment.