I bought a set of aircraft scales to use for the GMC or what ever else. The set had two 5,000 lb scales and one 2,000 lb. Only one worked. Replaced two of the handle springs with a cut down Ebay spring.
To get them apart there are snap rings and discs that cover two socket head fasteners on the bottom which hold the top on.
These scales operate like a bathroom scale where levers press on the measuring part. These are hydraulic using a gage and a piston that the levers press on.
The brass screw is where the oil is put in. Two of these had o rings that failed and needed oil. At first I used oil that was too high in viscosity and the gages moved real slow. Drained that and put in thinner oil and it worked ok. Doesn't take much oil.
The black part is a diaphragm which the piston presses on. There was rust stuck on the diaphragm which came off with a vinegar soak and neutralized with baking soda.
Levers and top cleaned up
Two broken screws, one came out other not.
They did put steel inserts in the aluminium and that did come out.
Cleaned, greased and ready to reassemble
Stacked for testing, match pretty close 500, 750, 1000, 1500 and 2000 lbs